How To Tune For 10.5-12.5:1 Compression & 91-93 Octane Pump Gas Without Losing Horsepower or Torque! 

My take on plugs is different from most. I’m not a fan of big gaps, .025-.035” depending on the engine and ignition system being used. I like Autolite Copper and Autolite Racing plugs for most engines, which inevitably leads to an argument from someone who thinks NGK TR6 Iridium’s are gods gift to engines. I’m not a fan of “gimmick” plugs, it doesn’t need multiple ground straps, V shapes, Y shapes, U shapes, or any special metals. I don’t run platinum or iridium plugs because of heat range issues and inconsistencies I’ve had with them. And I’m not a fan of fine-wire center electrodes, I’ve seen many go “missing”. Also, plugs are cheap, and relatively easy to service, if you want longevity from spark plugs, keep the car stock. Heat range only needs to be hot enough to keep the plug from fowling at idle, gap needs to deliver a spark that’s strong and consistent. This is an area where people tend to overthink things and end up spending money they don’t need to. Copper plugs will typically last 10-15k in a reasonably maintained street application, and they should be checked every oil change or seasonally. Coppers are also cheap enough to keep a set stashed in the car if it’s a driver and can be changed on the road if you have an issue.

@@TheGT350Garage My thoughts exactly

What are you expecting, someone to come hold your hand while you change jets?

@@TheGT350Garage - Looking past the obvious, I would at least like to know what tool to pick up and what to adjust, and for what outcome I am looking for. I have an idea what I am looking for, but I came here to see if you had something special to tell me, that I dont know. Since you didnt mention anything about what tools to use, what to adjust and or tips n tricks, cant say I know anything NOW I dont already know. Was all that, just to say "set your a/f to 14:1 on non ethanol gas and pull back timing? If so, I will give you 10 minutes of credit while still demanding my 40 minutes of life back!

A very informative video. Kinda made me look at things a little different. It does make sense considering that how you tune a forced induction type engine i would imagine. I have been trying to figure out how to do this. I tried fiddling with the dynamic cr calculators. But they are all over the place. Would you have any examples in videos or upcoming videos? I have an 11:1 cr aluminum headed 383 chevy. And I have been trying to figure out if I could run a 224/224 110 icl/ 114lsa cam. And if I could install it on a 106icl. Running 91-93 pump gas.

@JoshF89 I do have a video in the works that will really help you. As for your cam selection at your compression ratio, it’s quite small and will make far more cylinder pressure than you want. Duration will need to be 12-18° more than you have and the ICL/LSA numbers I use on high compression builds for street use are drastically different than what you’re describing. If you’d like to discuss cam selection further, please shoot me an email to thegt350garage@gmail.com and we can go from there.

@@mistersniffer6838ok ok in

There is more on this subject in the works.

Thanks. I’m working towards new content on this subject very soon.

You could only run 28 mph on the highway? Damn, should have geared it differently, that's slow as f***!! My car would whip dat ass! Talk about getting gapped!! ROFLMFAO!!

He was clearly implying 28mpg not 28mph.

Without the benefit of a knock sensor to detect the threshold of too much spark advance, it’s a bit risky to run 87 octane above about 10.5:1 compression. But with a knock sensor, I’ve run 87 octane win fuel injected engines as high as 13:1 with good results.

I’m originally from SoCal and lived there until 2017. If you run a vacuum secondary carburetor it senses demand and opens less at higher elevations. You basically just tune the carb as if the tune was for “elevation” on the primary side, and at 3500ft you’ll want an AF ratio of 12.7-12.9:1 at WOT and 13.3-13.5 at cruise. Easy to do with a Holley 4150 Vacuum Secondary, you’d just need the big 870cfm model. For the lower elevation tuning, you’ll leave the primary side of the carb alone and increase the jet size 4-6 numbers so that your AF ratio is about 12.2-12.5 at WOT and so you cruise in the 13.0-13.2 range down in the IE. The numbers sound rich, but the fuel in CA is heavily oxygenated and burns like a leaner mixture with its lower stoichiometric air-fuel ratio of 14.0:1-14.1:1. I used to live in the AV and I’ve run cars at LACR, Famoso, and Irwindale, all using the same tune, and driven them at 4000+ft elevation over the Crest, the Grapevine or Tehachapi to get to the track. If you’re still building the engine, the big Mopars like compression, I wouldn’t hesitate to go 11-11.5:1, then run a bit more cam and let the cam specs help you arrive at a dynamic compression in the 9.0-9.5:1 range. If you use the information I provided about timing, and I’m doing a follow up video to give even more insight into building the timing curve, you’ll be able to dial it in so you don’t have drivability or temperature issues.

@@TheGT350Garage thanks for the reply, it means alot to me right now, I am currently reconfiguring this engine, and yes, it appears that 9.0 to 9.5 is what seems right...but the common "thought" is saying I need to be at 8.5 to be "safe"....I actually have flat tops in it now that are .025 down in the hole..I'm showing 11.3 static, but they are sitting. 025 in the hole right now.. I was thinking about getting new pistons with a 12cc dish to put me at 10.6 or a true 11.1 if I take a bit more off the deck..I think with the quench issue, this would be best.(but I'd be interested in your opinion) I'm using the Trickflow heads with a 78cc chamber so I think this setup would be good.ive see 3 builds with these heads, and 32 to 34 degrees totalis what they seem to like best, this falls in line with your timing strategy from what I can decern..I'll probably go with a 250 @ 50 cam like you suggest...I already have a Ultra 850 HP carb, which may be a bit counter productive, but I will probably stick with it seenings that my car is a 4 speed....I'll be looking forward to your next video!

The “conventional thinking” of the past 50 years still holds a lot of guys back, and combined with a very poor understanding of modern fuel, it has lead to many an argument surrounding the operation of high compression engines on pump fuels. On my 289 Ford, the static compression is going to be 12.0:1. The intake valve closes at 70°ABDC and that comes in at 9.09:1 Dynamic compression. In reality it’s higher than that due to cylinder filling characteristics and other factors, much as I describe in the video. If you want to provide more cam info we can discuss the details specific to your engine. I will say a flat top with quench is better than a generic dish at “zero deck”. If you really wanted to fine tune the combination for a specific compression ratio, you’d want the piston at zero deck and an inverted dome (a dish that mirrors the shape of the combustion chamber to limit quench and control the charge better. Your 850 HP Ultra carb is A LOT of carburetor for street use. Not the CFM rating, that’s fine, it’s the extremely adjustable nature of those carbs that get a lot of guys in trouble. You will need to study what all of the various adjustments are doing and carefully adjust accordingly. It’s going to take some effort to truly understand how capable that carb is and make it work for your needs. I would also suggest splitting the difference from an altitude perspective and tune to the middle, meaning if you live at 3400ft and you’ll occasionally get down to 600ft, tune the car to operate best in the 2000-4000ft area and don’t beat on it at lower elevations with higher air pressure and density without verifying your AF ratio. (Investing in a wideband AF Ratio sensor kit is prudent, and about a $400 expense these days for a dual sensor kit.)

@@TheGT350Garage well, I have a hand full of cams on hand, and I'm ready to pull the trigger tomorrow on pistons if needs be. This is a "back up" engine for my 528 Hemi that I will pass on to my son eventually. I don't want to make it too complex for him, but I don't want a "girley-man" engine either...looking for a maximum effort pump gas engine. I've got a 243 @ 50, with a closing on intake at 46 This is a trickflow hydraulic roller that is pretty popular, and I've got a solid flat tappet with a 260 @ 50 duration with a closing at 54...I think this is a bit outside of where I want to be, but I've seen it done before in Diamond bar with a similar engine I built 20 yrs ago with the same problem (I gave up on it because it rattled on pump and I was outta $$$ and sanity)...I've got new tappets and pushrods for either setup, and I could see going either way..but for simplicity probably stay hydraulic roller. Yes, the HP carb is a bit complicated, but that is what attracted me to it. I've had Fuel curve West fully prep it, so it should be a barrel of monkeys at some point.

Depending on how you calculate dynamic compression, by using duration at 0.050” vs 0.006” you get very different numbers. Going back to my combination at 12:1, using the .006” duration gives 9.1:1, but using the 0.050” duration value gives 10.7:1. Your cam spec is at 0.050”, with 11:1 would give 9.9:1, but using the 0.006” advertised duration it’s 8.3:1. Between .050” and .006” the valve is closing with the piston rising and you will have reversed flow out of the port against the air mass stacking on the back side of the intake valve, so it’s going to be something in between those numbers. You should be fine running around 11:1 with that cam. If you want to fine tune it, you can advance or retard the cam 6-8 degrees from where it’s ground to get the desired result you want.

You are in luck, because there are more videos coming to dive into how ignition timing can needs to be set up, how to address the various functions of carburetors to achieve ideal air fuel ratios under various conditions, and how to use the tools that are necessary for making it all come together.

Hi Walt. Guido here. I am running like 5 gallons E85 to 10 of 91 chevron here in SoCal. With that amount of Corn fuel. Do I still adjust on my 4160 holley 1.5 turns out for Air Fuel mixture or a different setting Keep up good videos. Running 12 Degree initial. Total about 28-30 I believe.

@@luckyluciano4968 we should talk about this witches brew of fuel you’re using, it’s too hard to duplicate if you find yourself in need of a refill. It’s far better to run a commonly available grade and tune to it. I suspect you’re probably quite lean with that mix unless you’ve jetted up substantially. And that concoction would require substantial changes to the carb to make it meter the correct amount of fuel, beyond jetting, you’d need to get into the air bleeds, the PVCRs and do a fair amount of tuning. Your timing is in the range for a 10.5-11:1 compression combination, but until you get on top of the air-fuel ratio and get it optimized to the power potential of the engine, your timing settings are a wild guess at best.

@@TheGT350Garage I havnt jetted differently I was just trying out the E85. It’s a stroker 331. Is it spec out at 10.5-1. Coast High Performance in Gardena. Built the engine back in 2014. I don’t plan to keep it in the system. Gave it a little more pep. Havnt mess with anything Thanks for your input.

Just to put this in the simplest terms, 5 gallons of E85 (85% Ethanol) 108-octane mixed with 10 gallons of California spec E10 (10% Ethanol) 91-octane will produce E35 (35% Ethanol) 95-octane fuel. While that seems “good” it’s really not because you have to look at the effects on the stoichiometric air fuel ratio for each blend and that’s what determines what is rich or lean for the fuel. Gasoline has a stoich point of 14.7:1. Ethanol that has a stoich point of 9:1. When you blend them the stoich point “moves” with the blend ratio. E10 (10% Ethanol) 91-octane has a stoich point of 14.08:1. E85 (85% Ethanol) 108-octane has a stoich point of 9.85:1 Your E35 (35% Ethanol) 95-octane fuel blend would have a stoich point of 12.70:1 A 331 Stroker with 10.5:1 compression and a typical street type hydraulic roller cam grind (425-450hp) is going to make its best power on ethanol free gasoline at an air fuel ratio of 12.8:1 to 13.2:1 and 32-34° of total timing. The timing would stay relatively the same and at most 1-2° less depending on the fuel used for any of the various aftermarket head options and their different combustion chamber designs in concert with the various cam profiles that would all result in similar performance. What’s important to realize is that for the engine to maintain its full power output capabilities, you have to maintain the same amount of fuel energy and that’s why we need the Lambda number I talk about in the video. So knowing that straight gasoline with a stoich point of 14.7 makes best power at 12.8-13.2 we divide the A/F ratio by the stoich point to get the Lambda value range of 0.87-0.90. If you apply that range to the ethanol blends we’re talking about, here are the numbers: E10 91-octane (14.08) 12.5-12.7:1 E85 108-octane (9.85) 8.6-8.9:1 E35 95-octane (12.70) 11.1-11.4:1 In this day and age you need to verify the air fuel ratio of your tune. It’s just flat out important. And in most cases, you will need to adjust the carburetor jetting to optimize the air fuel ratio for the fuel in your region. Being in SoCal, you can’t get Ethanol-Free fuel that meets CA emissions requirements. Here in the Rockies and all over the midwest, Ethanol-Free is commonly available, and at the lower elevations with as much as 93-octane. These are the challenges of tuning cars on modern fuel. It’s not that the fuel is bad, it’s just more complicated. If you can take the time to understand it, it’s actually very capable and will do what you need it to do for you.

The cars from 72-81 that were still remnants of the 64-71 era were all neutered by emissions laws, but those cars are often upgraded to use higher compression ratios and have their emissions equipment removed. It’s nitpicking at best to include those lower compression ratios in the discussion as “muscle cars” because the muscle was gone and they were just cars at that point.

If you had a fairly decent cam in the engine that makes complete sense. It also depends on temperature, elevation, and some other factors. One of my favorite 302/5.0L Ford combinations 20+ years ago was a champion of 87 octane at 9:1 compression. It made 345hp to the wheels, about 415hp at the flywheel, year round in n 87. There was no gain from increasing the octane, it made slightly less power on 91. Back then I was obviously much younger and the guys I was working with were very stuck in the mindset that the fuel of the day was grossly inferior because they had experienced the Muscle Car era and I couldn’t possibly have any idea of what I was doing.

Thank you …timing and AFR all I wanted

@mikemaguire5507 if you don’t take the time to understand the difference between modern fuel and fuel of the past, you’re probably not going to get the results you want.

13.5:1 with a dome isn’t ideal. The dome interferes with flame travel. Shoot me an email if you’d like some guidance on how to improve the combustion event and make the chamber work better with the dome. TheGT350garage@gmail.com

The difference in timing is primarily because modern gasoline burns faster and more completely. Reading plugs is a good start, but it doesn’t capture the complete picture. Ideally, a tuning session on an engine or chassis dyno is the best way to find the ideal A/F Ratio and timing curve. But when those aren’t readily available, you can use a wideband oxygen sensor, a pyrometer (EGT Probe), and a simple stop watch to find exactly what the engine likes.

Thanks! I’ve had a rough year for making content, I hope to be back at it soon, but Part 3 addressing my stance on dynamic compression ratios is about ready to present and Part 4 isn’t far behind. I’ve compiled most of the work I’m presenting in the videos and may self publish it, or lean on some industry friends for a favor to get hooked up with a publisher. It’s always hard to get acceptance whenever you’re presenting ideas that aren’t popular or change longstanding opinions. Great feedback.

​@@TheGT350Garage I wasnt going to say anything until you mentioned trying to publish your knowledge to others. Back in the late 90's early 2000's I went thru an adventure on trying to understand the engine. The internet back then wasnt as helpful as it is now. In my few years of research I ended up purchasing 70 books. Back then I wasnt planning on writing a book, I simply wanted to understand the engine. In my early research I decided to put my notes in book form name it, "Dynamic Compression: Never Overcam Your Engine Again". Upon further research I changed the name to, "Understanding The Performance Engine Equation". I held off selling the book as I hadnt any process for the reader on how to properly custom match a Cylinder Head to the Block's Cylinder when upgrading performance: or how to qualify performance in general. I didnt want my book to be incomplete like everone else's book; full of pic's but no useable content. I had to figured out how the relationship changes between the Cylinder Head and Cylinder with each incremental upgrade in Engine Output? A year later, I finally understood. Life took me in another direction so I never really publicized my book, other than being on multiple bulletin boards. A guy in Brazil who owned a Custom Intercooler shop wanted my book. I sold him a copy even tho I was still in the editing process; he adamantly wanted it - guess that makes me an International Author; woo'hoo. He later sent me an email stating he never would've understood why the engine behaves the way it does without understanding dynamic compression. Engine math is Terciary, not one dimensional. Once you know what I call the three overriding parameters, you can Transpose your equations and know ALL parameters of someone else's engine. Ive said all this so you know, I know what your going thru.., I feel your pain. In our passion to work on, build cars, enjoy their performance, and teach others, you will always run into the disinformation crowd. I call them the never wanna say Volume Cult. I call them the Volume Colt as they've bought into only knowing a Cylinder Head's Intake Port's Pinch Point Area Sq.In. and never address how that Pinch Point Sq.In. is relative mathmatically to a specific Intake Port Volume. They are of the Volume Cult mind; remember tho, they are your target market. You'll go thru 100 heavily brainwashed ppl before you find that one person that says they wanna know more. We wanna teach and pass on our knowledge because of that one person that wants to know more, so be patient - which you are. You can always get published by someone. However, with the internet - self publishing is always an option. Create your own website and automate the sale of your book, digitally. My book in paper form was over 600 pages. Once you have your book in Ebook format, your talking kilobytes. Bandwidth is much cheaper now days than it was in the late 90's. If you go the self publishing route keep in mind if you go cheap on the Bandwidth your website will buffer on your customer's end. Dont know if you are knowlegeable on how Bandwidth providers divi up the Tower wherein their websites are stored. If choose minimum bandwidth, your website is shared on a Blade within the Tower until that Blade is full. If you choose unlimited bandwidth, you get your own Blade, your customers are happy as there is no buffering. The problem I didnt like about trying to sell my Ebook was how easy it is to Page Copy from the Internet. Can you actually stop ppl from buying or copying your book, repurposing your book as their own, and what are you willing to do when someone violates your copywrite. Another question that I realized was how many copies would I have to sell to make my efforts profitable? Bandwidth costs from the late 90's was the hurdle I couldnt get over, maybe you will have better luck as bandwidth is cheaper now days. Anyway, hope I was able to throw some things at you to think about.

@kevinshasteen5682 I’m not to the point of being able to publish my work yet, too much to do, minimal time because my day job is teaching young automotive technicians engine operation, diagnostic practices, emissions technology and preparing them for ASE A1, A8 & L1, L3, L4, & G1. My student have passed over 65 ASE certification tests so far this year after completing my classes. I’m very proud of my students who push themselves to achieve their goals and get hired into the industry with guaranteed wages as apprentice technicians instead of being stuck in a lube pit somewhere. I actually don’t like using “dynamic compression” at all. It doesn’t work, the science, physics and thermodynamics involved easily disprove its value. Modern automotive engineering has adopted “effective compression” as a result of the simulated Atkinson cycle and this is a scientifically accurate approach that addresses real conditions. You’ll like the next video. And on the topic of hosting on the Internet, bandwidth is a concern, copyright infringement is a major concern, and how to disseminate the content is not straightforward at all. I know several magazine editors and automotive authors who have published books and articles over the past 30+ years and I’ll probably try to work with one of them to make a book happen with a known publisher when the time is right. There are a few of them who I might convince to lend their blessing to the book. Time will tell.

You are a teacher, explains why your so good at it; your students passing their tests are indicative that you are an effective teacher! Dynamic Compression is only ineffective if you use 1950's parameters. Dont dismis the process simply because the #'s are outdated. Update the #'s so your equation for the process will be updated. The numbers can blur the lines the more efficient your engine becomes. Fuel Injection can be very efficient, more efficient than carbs - some will argue otherwise. So junk #'s in equals junk #'s out which is why I changed my books title: it was incomplete on its own. Ppl's minds will open when they undetstand Dynamic Compression - so, its still a good teaching tool. Looking forward to your next video.

@kevinshasteen5682 I suspect your numbers probably lean hard on what is now termed Effective Compression to be able to get things right. I think you’ll find the next video a satisfying watch, and I’d be happy to compare more detailed notes via email after you’ve had a chance to see where I’m coming from with it.

I’m doing a couple of follow ups to this video. I’ve decided I need go into far more detail about ignition timing with one, and dive deeper into the fuel discussion in another. I’ll also be doing some additional video content that will simultaneously support my assertions in this video, explain the content I’m sharing better than the presenters, and probably stir up a bit off a fuss unintentionally.

If a 351C uses a relatively flat piston and has .035-.050” quench with a closed chamber, that’s most of the battle. 11.3:1 needs an IVC event around 75-85° ABDC at .004-.006” (286-294° Advertised Duration) or 45-55° ABDC @.050” valve lift using a cam with about 234-238° duration @ .050”. ICL needs to be 112-114° at that duration to close the valve in the correct window. Using an LSA of 108 or less is too tight and disrupts idle and causes drivability issues, 110-114 depending on the final duration number is the range to be in to manage overlap, 116 and up is unnecessary except for extreme setups trying to run 255° @ .050” or more on the street, and there’s no benefit to a cam that large below about 13:1 compression. Cam specs are super important, but following some of the long time standard advice to advance the cam and tighten up the LSA is not conducive to quality results and just nets a lousy idle quality and pesky torque curve. My little 2.3L DOHC builds 20 or so years ago were 11.5-14:1 compression. I ran durations ranging from 226-256 @.050” and degreed them on install but adjusted them on the dyno to optimize power. Each grind had its own characteristics and each compression ratio had its ideal grind. At just under 140” displacement, to make 285-315hp at the flywheel naturally aspirated in the 7500-8200rpm range depending on the build was a pretty decent result back then, and most of them ran exclusively on 91 Premium pump gas. My 12:1 “street” build was 265hp on 87 octane and managed 35mpg on the highway at 75mph or so. Funny side note, the 2.3L DOHC heads ported flowed more than a lot of 4V Cleveland head with epoxied runners and port work, and with near 4” of stroke the ports moved a lot of volume, we were regularly over 100% VE with those engines.

While it often gets called de-tuning, the reality is that tuning is finding what the engine wants. Here’s a little food for thought: 9:1 static compression is calculated using 14.7psi atmospheric pressure at sea level, which is why a typical 9:1 engine pump’s slightly higher than 150psi (9 atmospheres + 1 atmosphere). Take that 9:1 engine and supercharge it with 7.5psi manifold pressure. That is roughly 1-1/2 atmospheres. Now the engine is compressing 14.7+7.5 = 22.2psi. 9:1 at 22psi is close to 220psi and we ran that on supercharged 5.0L HO Fox Bodies in the 90s with minimal tuning. Your 13.7:1 compression is not much different except for it being there all the time not just at high rpm. 13.7 atmospheres + 1 atmosphere = 216psi. There really isn’t much difference difference between tuning a 13.7:1 450” engine and a 9:1 300” engine with 7.5psi, they both have about the same cylinder pressure, if one was a 351W based stroker and the other was a 302 based forced induction engine, and both used the same head and combustion chamber on a flat top piston, you’d be shocked to find that while the forced induction engine would have a higher BSFC the timing would be nearly identical. The point being that if you can run a supercharger and have the equivalent of 13.7:1 compression on 91-93 octane, you can run 13.7:1 on pump gas if you take the time to understand what the engine wants.

@@TheGT350Garage yes sir I have learned that hi octane fuel is kind of a cheep fix for poor tunners .thanx for the insight

Once you pass the stall speed, the load on the engine increases. You probably need to look carefully at timing as well as fuel. I would suggest a vacuum gauge as well as the AFR info, you can judge load from vacuum, and you can use that to judge the appropriateness of the A/F you’re seeing.

Building a 10.8:1 460. This is my biggest concern when I finally run it

10.8:1 with a 460 isn’t really a big deal, as long as the piston is a flat top you’re in decent shape, just be aware that the chamber of a stock iron head is not ideal and timing is going to be in the mid 20s (25-28°) on modern fuel. Aluminum heads with redesigned chambers will want a bit more timing but not much (27-30°) on 91-93 octane pump fuel. If you tighten up the quench you’ll improve your resistance to detonation while getting closer to 11:1, simply by running a Cometic gasket matching your bore size and selecting a .030” thick gasket. Alternatively you can deck the block to 10.300 like a 429CJ/SCJ and use a .040-.045” gasket to fine tune the combination.

A 13:1 Boss 302 is a wicked combination, check the piston to deck clearance (should be zero) you want to really tighten up the quench area to about .040” (just the thickness of the gasket, no more. The closed chamber Boss/Cleveland heads do benefit from more cam duration and carefully chosen cam timing events to get the best out of them. In 11:1 or higher Cleveland and Boss 302 engines using iron heads, I install Autolite Racing AR25 spark plugs because they are a cold plug and produce good results. The AR25 is a much colder plug than an Autolite 23 (Autolite 25 is stock) or NGK UR5, I avoid platinum and iridium in these older engines, because they are designed to run hotter and self clean in modern engines with knock sensors and the computer can sense and catch the early signs of detonation that can wreak havoc on our older engines. I also run tighter gaps with high compression to improve the intensity of the spark, typically in the .028-.032” range with compression over 12:1 or when running boost (artificial high compression). Basically if your ignition system is up to the task, the cold plugs will work perfectly, you need a quality spark, but don’t want the spark plug acting as a glow plug. As for timing, the chambers are a good design, but I’m assuming you have a dome to get the compression that high and that really kills combustion efficiency. I shoot for the smallest chamber and flattest piston possible in small displacement engines, in big displacement combinations like a 408 Clevor, I use the small chamber and order a custom inverted dome piston where the dome mirrors the chamber and still nets that critical .040” quench area. You may find that you can give up a little compression and gain some power by improving the efficiency of the chamber.

@@TheGT350Garage thanks for all the info, it gives me much to think about. Yes I’m using Autolite25’s, car ran strong until my son let the fuel get stale during winter and then took it out on the back roads to warm it up. I suspect that the head gaskets are blown, yes it was zero decked. I’m using ARP head studs, also cam lift on paper was 0.540 but with the .030 clearance, if I go any tighter I run into coil bind. So maybe I should address all of this during this head removal. I dont have the cam card handy. Thank you for answering me. You can see my car on my channel called Laut Burns!

I teach engine controls and that includes VCT/VVT operation modes. Newer production engines are using late intake valve closing to produce Atkinson Cycle operating conditions. To operate in that cycle the closing event needs to be able to move from as little as 30° ABDC to as much as 120° ABDC seat timing. My cam isn’t “huge” and it closes on the seat at 81° ABDC, 55° ABDC @.050”. The way the calculators determine dynamic compression simply lacks any accounting for the rest of the physics involved and completely ignores the compression to expansion ratio of the engine which is equally important.

So, I did a follow up video where I explained how to use Lambda (combustion efficiency) instead of air fuel ratios for adjusting fuel. Ideally you’ll be in the 0.85-0.88 Lambda range for optimum performance on pump fuel. Lambda is independent of the stoichiometric ratio of the specific fuel you’re using, because it focuses on the completeness of the combustion process for the specific fuel you are using. Adjusting timing and fuel should be a rough timing adjustment somewhere less than you would expect peak power (2-3 degrees less) prior to adjusting lambda into the 0.85-0.88 range, then a fine adjustment to timing to get peak torque across the range. As for cam selection, I like a wider LSA than DV recommends in most cases for a street car. Typically I like a 112° LSA on a SBF. But in conjunction with the wider LSA I also prefer the ICL to be in the 112-114° range, not the 102-104° range that gets so much attention. What I’ve found is that the ICL has a far greater impact on idle quality than LSA, and simultaneously running the ICL about 10-12° “retarded” improves cylinder filling at higher engine speeds extending the usable power range while also improving idle quality. Just retarding the ICL would also retard he ECL but increasing the LSA advances the ECL. For a cam with a 110° LSA using an ICL of 110° ATDC, you would have an ECL of 110° BTDC. Example 1: Retard the ICL 4° to 114°ATDC and the ECL moves to 106° BTDC on the same LSA of 110°. Overlap does not change. Example 2: Widen the LSA to 114° with the same ICL of 110° ATDC and the ECL moves all the way to 118° BTDC. Overlap reduces 8° Example 3: Retard the ICL 4° and widen the LSA 2° to 112° and you get a cam with an ICL of 114° ATDC and an ECL of 110° BTDC. Overlap reduces 4°. In example 3 you retain the same ECL and this the same exhaust closing event, which is critical for scavenging the cylinder and creating a vacuum in the cylinder at TDC. By opening the intake valve 4° later you spend less time with the valve hung open during piston dwell at TDC and ultimately produce a better idle quality. It’s often argued that retarding the cam is only done for emissions and that it hurts low speed torque, but I’ve found that the losses are negligible off idle and the overall power delivery is more linear and efficient, with substantial gains to be had in average power across the range, and often 600-1000 more usable rpm at the top end. The one caveat to all this is you need to set up the vehicle correctly to make use of the power curve, and the rest of your components need to match your engine combination in a complementary manner.

@@TheGT350Garage I saw something about Lamda toward the end of this video, but how do you adjust it to weight of car? Heavier the car or truck, the more susceptible to detonation. (Maybe you answered this already and I am not understanding)

I really love your approach. I have a 403ci small block Chevy. I was wondering if you have an email I could message you privately to pick your brain some more. I have built engines before, but have not gone into this depth to get the most out of the engine. I would appreciate it if you would be willing. Thanks!

So, I do have a follow up video detailing the difference between fuels and focusing on the importance of Lambda. Basically lambda is a measure of combustion efficiency where ideal combustion is the relative stoichiometric ratio of the fuel in use. Most performance applications will make optimum power from a Lambda value of .85-.88 with rare exceptions getting as rich as .82 or as lean as .92 lambda. You’ll want to target a timing value 3-4 degrees below optimal for dialing in fuel, get in the range for fuel and then dialing in more timing, readjust fuel, and repeat. Ideally a loaded dynamometer is the fastest and easiest method to dial it in, but any method of measuring acceleration over distance and time will suffice as long as you test in a repeatable way under the same conditions.

My email is in the video description.

10:1 is absolutely fine as long as your quench clearance is .040-.060”. Any more than that and you start getting detonation in the quench area. If you’re using a dish and it doesn’t match the shape of the combustion chamber that’s also problematic. But 10:1 is a good starting point. You want to make sure your cam duration and specifically the opening and closing events produce the ICL, LSA and thus overlap you need for best results. People tend to get in trouble by using too small a cam or running a larger cam that leans towards building too much cylinder pressure in lower to mid range operation, and that too complicates the process.

@@TheGT350Garage it's actually a 1.8 ltr. mgb engine, very slight dish, 6cc, kidney shaped chamber. Presently at about 9.5:1, runs great on 93 octane but below that, I really have to back off the timing. the head is cracked across two seats, been running fine for the last 20k but feel like it's just a matter of time before it fails. I acquired another head but later found that it was skimmed .060 and think it would take me above 10:1. I have I new stock cam and runs great, smooth idle. Do you think a light porting would positively tone down posible detonation, thanks in advance.... Luc S...

@lucsavoie9501 port the skimmed head lightly to improve airflow, simply working in the bowl to contour the guide bosses and remove any casting flash or machining peculiarities in this area of the port and profiling the combustion chamber to unshroud the intake valve, and lay the deck back down to the seat with a gentle transition inside the gasket opening along with getting a slight 1/16” or so radius on the chamber anywhere it’s exposed to combustion combined with a proper valve job, and you can make big improvements in about 4 hours time plus the valve job. Then get a “Fast Road” type cam with duration in the 260-270 range to take advantage of both the compression and flow, you’ll have a very fun little combination. The one thing to consider is the piston to deck clearance, I generally build to 0.000” and set piston to head clearance with the gasket. Ideally you’ll want 0.032-0.035” clearance, if that clearance is more than that because the piston is below the deck, and you can’t get a thin enough gasket to get in that range, consider decking the block. It will further increase your compression but substantially decrease the likelihood of detonation in the quench areas.

Every fuel behaves differently but all fuels are predictable. Ignition timing is mostly about getting the peak cylinder pressure in the right place, some engines even like a bit if high-rpm retard. Cam timing is another discussion completely, and one that has to be had when discussing cylinder pressure and ultimately ignition timing. 35 years of doing this and I’m still learning new things, things that cause me to try new ways of approaching engine building and car construction as a whole.

@@TheGT350Garage you are 100% I’ve been racing since 1971 still racing have a national record still feel I’m behind .I’m impressed with your knowledge and that’s hard too do.

I appreciate the kind words.

My 2.6 liter I'm going to increase its compression from 8.7 to 1 to 10 to one on street gas I was reading that it can take it is that reasonable

If you are increasing it correctly by reducing quench areas you’ll be fine. Ideally you’ll want a bit more cam, but if you’re not changing the cam, you’ll want to retard it a few degrees to get the most from the added compression.

That’s in the works for sure. The distributor curve video I did shows how to make the change’s internally in a Ford Autolite or Motorcraft distributor, Mopar and AMC are very similar, GM is easier. As far as the process of figuring out where you are and where you need to be, that is a video that is waiting for me to have a running engine to film the process, and the same goes for carburetor tuning. Now, I will say, there are some basic tools at minimum required for tuning, timing light, vacuum gauge, but you will also need a wideband air/fuel ratio gauge and sensor. It’s a small expense relative to dyno time and stays with the car. All of this will be covered as I get the car out on the road for tuning. A final item is a g-meter and stop watch or digital accelerometer to measure acceleration over time, which is exactly what a dyno does. You won’t get an exact horsepower or torque number but you can measure gains or losses from changes to air/fuel ratio or ignition timing, and that’s more than enough in most cases. I’ll cover all of it in detail soon.

That head has a small compact chamber but it’s a less than ideal shape. Depending on the pistons and head gaskets you chose and how you machined the block you should have no more than about .055-.060 quench. That keeps you out of trouble. Don’t run a traditional spark plug in that engine. I use the much colder Autolite Racing AR32 gapped at .032-.035” and it makes a huge difference in fuel sensitivity. It’s not the cam alone, it’s also the fuel that drives the timing down into the 28-32° range. Make sure you’re using vacuum advance On manifold vacuum and the engine will run nice and cool.

Preignition is ignition before the spark. It can occur as a separate event from the spark ignition and still be a detonator event.

Thanks. There are certainly some who disagree with this, but I’m ok with that.

‘72 was the year compression ratios dropped, not ‘71. There were still a few hold outs that got through into ‘73, not many, but ‘71 was still a good year for factory muscle cars.

More to come!

Cylinder pressure is cylinder pressure. As long as you don’t have unrealistic expectations about your timing numbers or Lambda/Air-Fuel Ratios I don’t see a problem here. At 13.5:1 static and 15psi you’re at 27:1, this is equivalent to 9:1 static with. 30psi. The difference is you’re going to create the same cylinder pressure with less air and fuel, which means it will be more efficient than the 9:1 combo would be. You’ll use less total air and fuel to make the same power in the same engine with more compression and less boost pressure. I’ve done this nearly 20 years ago with 2.0L Fords, not quite to this extent, but I transitioned from 8:1 with 15psi (286hp) to 10.5:1 with 12psi (338hp) in the same engine. To make over 50hp more from the higher compression combination was astonishing at the time, and clearly demonstrated that combustion efficiency was more important than airflow. I saw lower EGTs and was able to run slightly more timing to achieve the final output, and in both cases Lambda was about 0.78 at peak torque and 0.82 at peak power. Seriously, best of luck.

​@TheGT350Garage thanks for your response! I had the same outlook with cylinder pressure having stuffed 60psi into my 2.2 4 banger for many years on 9.1, low timing figures around peak torque is always the way we tuned to make them live, but yes we'll be super cautious and depending on how it goes drop it a little if we need to, but comp is new to me and I'm excited to feel it! In fact, given this has such high comp, we will tune it like it's a stock bottom end 4 cylinder and let the cubes do the work.

I thought I had responded to this, so apologies for the delayed response. The cylinder pressure is a little higher than some like, but not terribly so. If it’s not beating up valvetrain parts, it’s probably ok to keep the cam and compression where it’s at. If you’re at sea level, 14.7psi, you can determine the effective compression ratio from your cranking compression. (205/1.4)/14.7=9.96 so call it 10:1. That’s effective, not static or dynamic. If you’re above sea level pressure drops .5psi for every 1000ft elevation. This would only mean the effective CR would be higher. If that’s an old school cam grind, the numbers may be advertised numbers and the cam may be much smaller than you think, ideally compare numbers from the @.050” duration to get a better sense of how big the cam really is. More cam could lower the cylinder pressure and make the engine easier to tune without giving up performance.

Cleveland 4V with closed chambers wants compression. The improved combustion pressures get the ports activated because the piston on the companion cylinder accelerates at the same rate as the piston on its power stroke. Bigger cams become more effective as a result. It’s not about valve closing and dynamic compression though, that number is actually pretty meaningless, and the only reason it continues to be used is because everyone wants to run too much ignition timing at lower speeds and detonation is the result. You talk to cam grinders and they all push advanced cam installations, yet the closing point is the supposed secret to success with respect to cylinder pressure, and those two things are in conflict. I’ll be sharing my full thoughts on dynamic compression in an upcoming video and it’s going to explain a lot about how the engine combination works and why dynamic compression is utter BS.

@@TheGT350Garage I'll be looking for that.

I appreciate the thought that went into the comment but there are other factors you aren’t considering. The ethanol content of the fuel has a cooling effect that negates some of the heat, as does the pressure drop into the cylinder, much like expanding a refrigerant to create air conditioning, the void created as the piston moves down the cylinder is going to cause a low pressure for the air-fuel charge to expand into and that too will cool things down, so it negates much of the heat you’re adding in using polytropic calculations. Sometimes it’s better to simplify than over complicate. This is one of those times. Otherwise we would have to calculate the rate the cylinder volume increases and plot that against the flow of the cylinder head, at which point we would see that the expanding volume is greater than the head flow initially. Then we would have to factor the speed of the crank, the length of the rod and the acceleration and deceleration of the piston against the speed and mass of the airflow, at which point we could roughly calculate how much air flows past the valve while the piston is in a practical state of dwell near BDC. Easier to run a compression test, take a pressure and see that it is more or less efficient than the static compression ratio as a determination of overall pumping efficiency and potential volumetric efficiency / performance.

The only way you can get 47° under load with vacuum advance is running ported vacuum. Manifold vacuum will be 2” or less at WOT and you’ll have 34° at WOT. That’s why I take the time to explain the difference, and if you skipped through the video you probably missed that part, and your comments would be more about the mistake you made using ported vacuum than trying to blame vacuum advance piston failure. You probably have too much initial timing and likely have a secondary issue with your starting circuit causing slow cranking. The only reason 102 “real race fuel” would make it start better is if it had a lower ignitability that caused it to make combustion pressure later or after TDC. Back the initial timing off and 91 octane will make pressure at the correct time for the engine to start normally.

Didn't mean to misguide the port vacuum with manifold vacuum. I installed the vacuum on the manifold, so when the engine is at WOT the vacuum goes to zero. It's when you start letting off the the throttle gradually, the vacuum goes sky high along with it goes vacuum timing , now your banging at 47 degrees and fuel is still moderately rich, causing detonation. I heard it with my 350 , not going to grenade my engine to try to experiment. I'll take the loss of HP, unless you have a way of doing it that won't destroy my engine . Good video , just a little hesitant.

@@johnszoke586 there is a reason I’ve made a good living tuning engines and now I teach and develop training for engine performance, drivability, and emissions compliance for one of the largest auto manufacturers in the world. Not bad for a guy without a degree. Your issues are not unique to your combination, and they are all correctable, without the need to perform experimentation or put the engine at risk. I do these videos to help people like yourself learn how to get the best from their setup, not to argue with them. The only way that works is if the viewer has an open mind to listening and learning. If you ask for help, that’s what you get, and if you complain or argue, well…

Indeed, it was already hammering away at nearly an hour and I thought that was a pretty long video. I’m going to be doing more on ignition curves, cam selection, dynamic compression, and more to expand on the topic because the response has been overwhelmingly positive to this video. Thanks for the input.

I agree with you that it is a great video. I do, however, suggest that the inertia of the fuel/air mass is directly related to engine speed thus raising a calculation conundrum viz., should you calculate dynamic compression ratio at some 'standard' RPM or merely realize that it will be higher, although it will likely follow some complex relationship (think 'non-linear' and 'fluid dynamics'). Thus cranking speed (in RPM) - as fuzzy as that variable is cannot be included unless other much more fuzzy variables such as, path length, path geometry, mass of air and mass of fuel droplets, Reynolds number, air density, etc., etc., are also included. You are right Braaap, it could have been mentioned. So much excellent, well researched info was provided.

Sorry, I should have said the "it will be lower", not higher.

To a greater extent you’re complicating separate concepts by combining them. Simplicity is key. The accepted logic behind dynamic compression is that it is related to the closing event of the intake valve during the compression stroke. So if the valve closes at 45° ABDC (1/4 of the compression stroke) the dynamic compression ratio will be 75% of the static (10:1 static would be 7.5:1 dynamic in this example). This number remains constant regardless of engine speed. If anything, cranking compression is the more useful value. Consider, atmospheric pressure at sea level 14.95psi (we’ll use 15psi for ease of math. If we apply the static and dynamic examples above, cranking pressure would be 150psi and 112.5psi. But a typical healthy engine with 10:1 static and a cam in the 270(adv)/215(@.050) duration range will pump 160-180psi depending on a few other variables like the actual opening and closing events, cranking speed, etc. The air velocity is easily calculated for the roughly 200rpm the engine should be cranking with the spark plugs removed and the throttles wide open. Mean piston speed and cylinder volume would get you close enough to have an idea. A 302 Ford at 200rpm with a 3.00” stroke has a mean piston speed of 100ft per minute. With a 4” bore the single cylinder is 0.02185cu/ft of air. So a single cylinder at that cranking speed is only capable of consuming a maximum of 8.74cfm per minute. Through a 2”x1.1” port the velocity at that speed is 9.53ft/sec, which is still fairly slow, and the mass of the air being 0.0807lbs per cubic ft, you could reasonably predict the “stuffing” effect of that velocity into the cylinder as the piston rises from BDC with the intake valve open to approximate the volume of gas in the cylinder. But this is SO FAR above the average enthusiasts head that it’s only good for a discussion with engineers, physicists, and car nerds of the most extreme order. I’m sure I could pull the data together into a spreadsheet and build a formula that would give us a better picture of the whole scenario but I’m not sure we’re quite there yet with my current audience. Thanks for the comments guys.

That is some explanation right there! Good info and very hard to come by. I did A LOT of googling on this stuff …..

Might want to rethink the idea that 91 can be leaner and have more timing. That’s not usually the way the fuel responds. 94 Ultra has a stoich point around 14.2-14.3, and 91 will be closer to 14.1-14.2 depending on the source and season. That puts you at .95-96 Lambda on Ultra 94 and .97-.98 Lambda on 91 octane, which, respectfully, is a recipe for disaster. Even “IF” stoich was 14.7 and there was no ethanol content in any fuel you were running, you would be at 0.93 Lambda on Ultra and 0.94 Lambda on 91 octane. Most high performance naturally aspirated engines need to be in the 0.86-0.89 range to be safe for regular use on the road, especially in the transitional range below to just above peak torque.

So atmospheres pressure is 14.7psi at sea level. If you add 20psi, it’s 34.95psi acting n the engine. That’s 2.35 atmospheres, so you multiply the static compression ratio by the atmospheres meaning 9.1 Compression is the equivalent to about 21.4:1 at 20psi manifold pressure. That’s a big number but it will still run on pump gas with EFI.

Open chambers are rarely used for high compression ratios though, and require big domes to get there, which further deteriorates the efficiency of the chamber. Modern aftermarket heads for older engines do have improved chambers, but these principles apply regardless, and I say that having used these methods to tune many Ford FE & 385 engines, and Mopar B/RB engines with period correct iron heads and little more than a performance camshaft. There are of course a few engines that really struggle due to open chambers and a complete lack of quench area like the Ford 351/400M in stock form, but if you want performance from these engines, you need to work with someone who specializes in them and can help you address these shortcomings as part of the build.

This isn’t a straightforward question. The transmission doesn’t determine the compression ratio. There is a lot of missing information, like is that the duration at .050” or the advertised duration (I suspect advertised). The @.050” number is a better gauge of cam size. If the @.050” numbers are in the 225-235° range, compression should be roughly 10-11:1, 235-245° 11-12:1. The 106° LSA is pretty tight and will work fine with higher compression, but there are a lot of factors that go into cam selection, and ultimately cam installation. The manual transmission won’t care what the combination is, just use a good clutch and gear the rear axle appropriately. A TH400 however will need a converter that matches the engine’s output characteristics if you want it to be successful. I’m not sure what you are looking for in the way of a safety margin for dyno testing. Be thorough and maximize the average power. Testing isn’t cheap so have a plan, stick to it. Start with 26-28° of ignition timing, get the air fuel ratio dialed in at about .83-.85 Lambda (slightly rich) maximize your ignition timing to find the highest average and peak horsepower and torque. Then fine tune the air fuel ratio into the .86-.88 Lambda range for the hero numbers. On the street I would pull out 2° of timing and jet up 1-2 jet sizes on all four corners of the carb.

@@TheGT350Garage Thanks so much for your reply.

The reason you can’t “go nuts” with the timing is modern fuel burns faster, not because it is bad.

I agree with softening but not “slowing” the chamber. I’ve applied the principles of the “soft head” and “groove theory” in building engines over the past 20+ years, and both when applied correctly work very well, but both require a rather tight quench area and a small combustion chamber to be most effective. For the average enthusiast, simply detailing the combustion chambers to remove any sharp edges is an important and easy step to pull the most out of the chamber, a basic softening technique. Even CNC machined heads benefit from a light touch with some abrasive, be it hand finishing with 400 grit paper, or like I do with Scotch Brite pad in a mandrel on a die grinder.

Iron heads retain more heat. More heat means less timing. Period. Not much more to discuss. Quench is a subject suitable for a video all on its own, but lazy open chambers, dished pistons that look like a cereal bowl, and pistons below deck are all cause for concern and disrupt the efficiency of the chamber. That gasoline was cheaper than ethanol was a major factor in Ford adopting gasoline over ethanol. General Motors (not Chevrolet) was not a factor in the decision for Ford to use gasoline, they were however instrumental in getting tetraethyl lead into gasoline along with Standard Oil (not Mobil Oil) and DuPont in 1923, more than a decade after the introduction of the Model T. Kettering, the engineer responsible for getting TEL into gasoline studied ethanol blended gasoline at length, and was convinced that a 30% ethanol blended gasoline was ideal, but ethanol could not be patented and all the players involved wanted to profit from increasing the anti-knock characteristics of gasoline, so TEL beat out ethanol. And it was lobbyists of Big Oil who convinced the government to tax ethanol out of competition to TEL. I’ve done the research, before I made this video, and I can cite sources as needed. My comments aren’t opinion, they’re research based on documents directly related to the discussion. Thanks for your comments, be careful stating things are facts without being able to support your claims.

If you use the same ignition timing and air fuel ratio at 8.8 and 9.3 you’ll need about 1-2 additional octane points, or as you’ve observed an increase from 87-88 to 89-90. Your assessment that the engine requires the addition of more octane is because you have ignored both the air fuel ratio and the ignition timing in the OE fuel injection. Optimize the air fuel ratio and you’ll find the engine can return to the original octane rating by running at .84-.86 Lambda and you’ll also be within 1° of the original ignition timing. Making the same if not more power than you are on 90 octane with the lousy factory fuel and spark mapping.

@TheGT350Garage Not having access to high end tuning equipment leaves me kinda going old school. With success I'm happy to report..using live data to monitor o2 sensors and fuel trim led me to a lean condition. Plug reading confirms this..a small vacuum leak was repaired and colder 3923 plugs installed along with low ohm wires has me burning the rot gut again 😆

“High End” tuning equipment is not really necessary. You can’t rely on fuel trim data from a narrow range oxygen sensor though. They can only detect Lambda (Stoichiometry). If the sensor’s cut point for stoichiometry is .450v (450mv) any time you’re below that you’re lean and any time you’re above that you’re rich, but in either case you have absolutely no way to know how lean or how rich you actually are. If your ECM was originally built with the assumption that the stoichiometric ratio of the fuel was 14.7, the sensor will perpetually give a lean signal to the ECM because modern ethanol blended fuel hovers in the 14.1-14.2 range. So your fuel trims will always show roughly +5%, or 5% lean, and if it’s an older (pre-2005 ecm it’s a challenge to interpret this). This is where you do need a wideband oxygen sensor and with kits in the $200 range now (they were $3000+ when I started tuning) it’s no longer a high end tool. If you adjust the fuel pressure up or use a slightly larger injector (assuming it’s speed density and not mass air flow) you can get back to the correct air fuel ratio without needing to reprogram the ECM. Whatever you do, you need to stop thinking it’s a fuel quality issue and realize it’s actually a simple adjustment to a slightly different stoichiometric ratio that’s needed.

It was an overly simplified explanation. Dynamic compression in and of itself is a BS metric. If you spend any time at all studying Atkinson cycle engines you’ll find that most large performance cams put the engine on the verge of Atkinson cycle operation. At that point we’re looking at compression vs expansion ratios and how we can optimize expansion and scavenging. There have been a couple comments to this effect. I’m putting together a video on “Dynamic Compression” for the channel.

Getting 12.5:1 from a 289 is a challenge without using a big dome. My heads are TFS Twisted Wedge and they are being milled to bring the chambers down from 61cc to 46cc, a 2cc dome, the block is decked to 8.190” and I’m running 12.29:1. It’s not a combination for the faint of heart or those who don’t give tremendous attention to detail.

@@TheGT350Garage did you have to cut a lot off your intake to get things geometrically lined up?

No. Because I’m moving the port up the face of the head and away from the deck, the majority of the port alignment is addressed that way. I was able to leave the manifold it’s original width, elongating the bolt holes slightly inward for bolt alignment. Doing it this way also means no machining at the end rails on the valley. But, it’s A LOT of work and time to get everything matched up. Everything is done on the gasket faces, but even the water ports had to be addressed to prevent water leaks.

I’m guessing you’re using a later 10.322” block and you don’t mention which pistons you’re running. If you have a flat top with eyebrow reliefs and you cut the deck to 10.300 you will be just over 11.2:1 compression. A dish will obviously be less, and the shape of the dish will play a major factor in combustion efficiency, by which, anything other than a dish that matches the shape of the combustion chamber will reduce quench area and impact flame propagation in the dish portion of the overall combustion chamber space. The reason I wouldn’t cut .036 off of the deck is because with the large bore on a 460 the piston will rock on the pin in the piston to cylinder wall clearance space and you get dangerously close to contacting the head with the piston at TDC. A big bore like the 460 needs .055-.060” piston to head clearance to avoid collision, but that’s still great for quench. Quench is a whole concept to itself that I will cover at some point in a future video. I’ve had some challenges getting content made for a while now, but I’m working on it.

@@TheGT350Garage Thanks for the advice. I have a set of Silvolite 1143H.040 with a +21cc piston volume. The block came out of a 1973 Lincoln Continental.

Take the deck to 10.300” and the D0VE-C heads. Take what you get for compression and quench. That piston is generic, the dish isn’t ideal, but the combination will work better than it would with the D3 heads.

@@TheGT350Garage I really appreciate the advice. The block is at the engine shop waiting for the pistons to arrive so they can mic them for the finish hone. I know the pistons are cheap ($220 for eight) but they are the only ones Summit had that were close to the CCs I needed. Diamond & Icon cost over a thousand a set. Keith Black also expensive. I will tell the machinist to go 10.300" and hope it runs ok with the Howard cams 240705-12 roller cam I plan to order. Thanks for your help

Honestly I would have used a Silvolite 3191H, compression isn’t the enemy. On 3.85 stroke with a 6.605 rod you’re .018” down the hole at TDC in. 10.300 deck, with a Felpro 1018 gasket. With a D0VE-C you’d have been right at 11:1. Your cam choice doesn’t have nearly enough duration. In the 10:1 to 11:1 compression range a street profile should be in the 234-238°@.050” range on the intake with an exhaust duration no more than 6-8° more than the intake, the ICL needs to be at 112-114, with an LSA of 108-110° and .580-.600” lift on both sides.

Fools and their money are easily parted. E85 is a joke, and the joke is on people like yourself who think it’s better than pump 91-93. The garbage they call E85 from the pump is wildly inconsistent and has to be tested tank load to tank load due to wild variations in ethanol content. Canned E85 is expensive enough you may as well run proper racing fuel. And if you’re only running WOT, you probably have a 12-15 second attention span so I doubt you grasped the concepts presented in this video.

Setting up a car for nitrous is basically setting up for naturally aspirated use. I run tighter plug gaps than most, .032-.035” and basic copper core plugs, nothing fancy, it’s of little benefit. With nitrous oxide you’ll be pulling about 1° of timing and closing the gaps about .002” for every 50hp worth of nitrous. So a 150 shot on an 11:1 SBF would have about 26-27° total timing and a .026”-.029” plug gap. A 110-120gph mechanical or electrical pump is sufficient for that setup, it will feed 550-600hp without issue. If you know you’re going to run Nitrous on the engine during assembly, you’ll need to increase the ring gaps .002-.004” for 100-150hp. If you’re planning significantly more than 150hp the build has to be adjusted further, but at that point you’re into a race block and if you’re spending that level of money on the engine, you’ll want to involve your machinist for things like piston to cylinder wall clearance too.

I’m working on better illustrations and probably going to get a white board.

Steve, check your email for a response, and if you have any questions please reach out again for follow up responses.

I’d love to have that discussion. I think DV has done great things for the industry, but I disagree strongly that dynamic compression is a valid metric for engine building and tuning.

@@TheGT350Garage with the greatest of respect, that’s a bold statement considering that man has been building race winning engines for 60 years....

And I appreciate that you respect his life’s work, I do too, BUT that does mean everything he has said and done in all his years is 100% accurate or true. Dynamic Compression is an older concept now, and it borders on taking the Otto Cycle into the Atkinson Cycle. At that point we aren’t talking about dynamic compression at all, we’re actually talking about the relationship between compression and expansion relative to time. I need to grab a 5.0 Coyote powered Mustang and strap it down on a dyno, pull it stock, lock the VCT tables and make a pull to show how much it loses, then incrementally move the cams around to show what happens with early exhaust openings, late intake closing and so on. I’ve done this years ago but lost the data to a failed hard drive.

@@TheGT350Garage would be interested to see the data. Thank you for the get back 👍🇦🇺🥃

I use @.050” values not advertised because advertised values are really inconsistent from cam to cam. The cam manufacturers have enough variation in their advertised numbers that they’re basically useless for comparison or any true closing point determination. Also, at .050” the valve presents as closed to both sides.

@@TheGT350Garage That makes sense,.. you never do see flow numbers posted for .050" values... lol. Thanks for the reply. Keep up the killer content. 🍻

@Torquemonster440 the flow at that point t is quite minimal.

The key thing to understand here is that timing itself is not what makes power, and more octane is not what makes power. Releasing the full energy content of the air-fuel charge and converting it into pressure is the goal, that’s more a matter of understanding the combustion cycle and the behavior of the air-fuel charge in the specific engine you’re working with. The timing still needs to be “correct” for the cycle, and the air-fuel charge needs to be the correct ratio to produce the energy required to reach a specific power output. Changing the temperature of the combustion chamber will allow more compression which will increase the temperature of the charge making it more reactive before you reach the point of auto ignition or allow more timing advance at the same compression ratio to increase pressure in the cylinder before causing spontaneous combustion elsewhere in the chamber which collides with the intentional combustion causing detonation. High compression has been used more and more in recent years but even with bikes, forms of variable valve timing are being used to manipulate the cylinder pressure. I’ll be sharing more information about high compression and camshaft timing soon.

In response to the 1st potion of your response. That is exactly what I said. To be more clear the design of the combustion chamber has more effect that anything when it comes to how much octane is needed..Also toluene does not increase octane. It was invented by the Renault F1 team back in the early 80's when they (F1 teams) were restricted to a 100mm inlet on the turbo and used a spec gas. Which I think was the unocal race gas. So by 83-84 they were making close to 1700hp.in Q trim and race tune at about 1450 - 1500hp from a 1.5 ltr. 4 cyl.. compression with 3 bar of boost static compression was 36:1 and higher toluene slowed the burn speed down and almost vanished spark knock forever Vp fuel C16 is 28% toluene. The F1 teams were restricted to 22% toluene is actually used as chemical flame retardant. Fireman suits.

@forcedinduction5245 you aren’t conveying cohesive thoughts in your comments, and a large part of what you’ve posted in this most recent comment is completely untrue. Toluene has been around for over 150 years, it was t “invented” by Renault. It’s not a magic elixir that cures all detonation even in high concentrations. 3-bar (4 atmospheres, or 45psi) resulting in a 36:1 static compression would mean a base compression of 9:1, but F1 (and Group B Rally Cars) we’re running in excess of 60psi. Of course combustion efficiency is key, but none of this has a damn thing to do with the purpose of this video.

You’re missing the context that compared to engines prior to WWII, an 8:1 compression ratio was relatively high compression at the time, wether it was considered high compression or not in period wasn’t the point, it was a substantial increase from the previous generation of engines. The development of high octane fuels after WWII allowed us to build what we consider truly high compression ratios of 10.0:1 and greater like the Chevelle SS you’re referring to. And in modern context, 10.0-12.5 compression ratios are not really “high compression” anymore, they’re quite common actually. I have a new video coming where I’ll get very specific about compression and cylinder pressure.

@@TheGT350Garage If you had said WWII instead of 64-74. I would not have left a comment.

@blackericdenice directly from the transcript: “By modern standards, high compression is any engine with a static compression ratio over 10:1, but prior to the Muscle Car era (from 1964-1974), 8:1 compression was considered high compression.” “Prior to” not during the Muscle Car Era of ‘64-72. I appreciate your comment.

Your engine really needs a vacuum advance distributor. It would take some stress off the starter and make it easier to crank with a lower current draw on the battery, and as soon as the engine builds manifold vacuum it would clean up the idle nicely. Your 30° total would be 12° initial with an 18° bushing and it would idle with 20-26° depending on the adjustment of the vacuum advance. At WOT the manifold vacuum advance goes away and you run strictly mechanical so you’re back to the optimal 30° under hard acceleration. What you’d see is an improvement in efficiency and drivability at part throttle and much easier starting, especially when the engine is up to temp.

@@TheGT350Garage Hi and thanks for the reply...actually it starts fine at any temps..has an aftermarket starter of some kind...but no kicking back or anything like that. Im also using an 85551 pro billet distributor that cannot accept a vacuum advance canister.

Try watching at 1.5x speed, lol. There is more to talk about than what’s covered in an hour video, the issue is not your ability to comprehend it, but that it’s a very complicated topic and takes time to understand. I’m in the process of moving into a Lee garage and have big plans for additional videos on this subject. The next video will go into detail on the topic of dynamic compression and break it down into a very different perspective than what most people are used to. As for your piston failure, it was probably a combination of too much ignition timing, and a lean air fuel mixture, perhaps even a quench issue. Most of which are completely avoidable.

I’m doing a follow up on how to set up the timing, including some things that will help make the timing curve easier to understand. As for jetting, E10 typically requires an increase or 1-2 jet sizes over ethanol free fuel. It also requires a small change (increase) to the power valve circuit restrictions. Ideally, you need a wideband A/F ratio sensor and gauge, better still is a way to data log the car and look at RPM, A/F, and MAP, you can plot timing against the data log after the fact. The only other parameter worth knowing is EGT from a pyrometer, that can be used for fine tuning the ignition timing. Without the tools to get the information you need, specific jetting and timing recommendations are little more than best guesses. They may be close, but they will still leave room for improvements.

You're welcome!

The principle applies to most engines. There are always exceptions, but I’ve used these methods on Ford, GM and Mopar engines with solid results. I’m working on a follow up video on how to dial in the timing curve step by step that I hope to have up in a week or two. The process works, and I’ll show some great examples in the process.

So, ethanol isn’t quite the demon it’s made out to be. It has some positive effects on combustion including better vaporization which has a cooling effect on the combustion process. Most “Ethanol” conditioners or additives for ethanol fuels are just methanol and fuel system cleaners. If the car will go into winter storage for more than 4 months, I’d use Sta-Bil or an equivalent product to keep the fuel fresh and fill the tank to 95-97% for storage to limit the amount of air that can oxidize fuel. Otherwise there is t much to be gained from ethanol fuel additives. As far as your jetting, you typically need to jet up a bit for E10, and that could do the trick. Also, your new carb may have a slightly more modern calibration to combat not just the changes in fuel, but also to run an air cooled engine a bit on the rich side to manage cylinder temperature better.

@@TheGT350Garage Thank you for your advice regarding the additive route. The carb is a new AMAL and for your advice on running a bit rich. I'd wager that there is no refining of the carb....🤭

...note the pipes blued up very quickly so it may already beset a bit lean

If you have 100 apples. And I take away 25% of your apples, you have 75 apples remaining. You’re calculating the difference between the final product and the original product and if we started with 7.5 and wanted 10 it would require a 33.3% increase to get 10, but we are subtracting or losing 25% here, so it’s 7.5:1. Comparing fuels is challenging. AKI is great for pump fuel, but race fuel in a can requires you to do some research. To call it “race gas” RON will be 100+ and AKI will be 96+ but even then it’s not that simple.

@@TheGT350Garage Fair enough... Though you didn't really hit on MON since it's rated under extreme stress (300 deg plus intake temp, 50% higher rpm) compared to RON(120 deg intake temp). Wouldn't that be a better metric to look at for performance engines? Seems like if the MON is particularly high, that means the fuel would be particularly less likely to grenade your engine under driving conditions that would cause catastrophic failure in the first place. Another thing that I've read, and this is from David Vizard, himself, is that water has "infinite" octane, and therefore water injection (not even water/meth, he says JUST water) can allow you to run up 14:1-17:1 on 87 octane fuel. What's your take on that? Is that even useful for the street or no?

@Drunken_Hamster David Vizard is brilliant, but there is a point where practicality has to be a consideration. What happens if you are driving and you have a water injection system failure? If you tune for water or water/methanol, you have to rely on the system to keep the engine from experiencing detonation, I’m a fan of simplicity, and water injection is not conducive to simplicity. As for MON, it’s not as readily accessible for fuel information as RON or AKI. AKI being the average is honestly the better choice for comparison across all types of fuel, but performance fuels don’t always include the information in the documentation. Again, simplicity being key to success, using a single standard for measurement would be ideal, but this industry isn’t as good about getting together and adopting standards as it could be.

@@TheGT350Garage I thought so on the water injection part. And thanks for the perspective on both! I haven't watched your second video yet, but it's in the queue. After all, I might end up throwing a 302 or 331 stroker in my Ranger some day and I'm learning a lot beforehand so I can do it right and put the whoopin on them 05+ muscle car boys. Especially them fat Mopars and my brother's 2012 SS.

Summary: Get the timing right at idle, enough that idle is stable and starting is still easy, using manifold vacuum for additional timing advance at idle and part throttle helps the engine run cooler and more efficiently, mechanical curve needs to be all in 200-500rpm above your typical cruise rpm with timing adjusted to make peak torque and horsepower. Idle fuel adjustment should be just lean of Lambda (quick refresher Lambda is the observed air fuel ratio divided by the stoichiometric air fuel ratio of the fuel you are using, the stoichiometric ratio varies with different fuel blends, octane ratings and geographic regions), with optimal timing you can idle at 1.02-1.05 Lambda with ease. Part throttle cruise should be in the .95-.98 Lambda range and hard acceleration, 3/4 throttle to WOT should land you in the .85-.88 Lambda range.

Altitude lowers the pressure which in turn lowers the boiling point of the ethanol. It’s a challenge. Have you considered using a heat barrier gasket like an Edelbrock 9265 or 9266. They are based on the gaskets used to separate the heat of the EGR spacer from the carburetor on emissions engines and do a good job of reducing carb temps. Another possibility is to install a return line and fuel pressure regulator (similar to early EFI systems) and put a cooler in the circuit to reduce the temperature of the fuel. I’m at 4500ft and these are things I’ve done in the past for operation at altitude.

@@TheGT350Garage All good Ideas what I have done is run a spacer between intake and carb also have a cobra jet scoop but it gets over 100* here and a black hood doesn't help even with heat extractors. 100% gas works the best ,for me. Also Aluminum heads allow for higher compression I run my 289 hard close ratio Top loader Detroit locker and 4:11 it's got just enough gear to be quick, smoke a lot of homies. I built the this pretty much like a 65 gt 350 all suspension mods hotter 289 but it's been fun for 41 years I've had it since I was 14yrs old.

Sounds like a really fun combination. The key to stopping the ethanol from boiling out of the fuel will be pressure and temperature control, which are hard to do in a fuel bowl. Short of keeping the fuel under pressure using fuel injection all you can do is seek out clear gas (ethanol free). We have 91 octane ethanol free at a couple locations here in northern Utah.