How To Tune & Use: Pump Gas, Race Gas, & E85 In Your Street High Performance Engine 

Lambda takes a lot of the misunderstanding away and corrects for the fuel being used.

So, I’m not a fan of “dynamic compression” as a concept. It honestly doesn’t work in my experience, and in practice it’s bordering on entry into Atkinson Cycle operation. I have a video in the works on the topi, and I’m trying to get to a point where I can show the concept better. It’s been a really busy year, but stuff is in the works.

In the works.

@@TheGT350Garage Looking forward to it!

​@@TheGT350GarageHey bro did you ever do that video?

Just got the last few pieces for the engine build, not only am I going to lay it out in detail, I’m going to build it.

@@TheGT350Garage How high can you go on 87? Is it possible to do 12-12.5 on 87 and retard the timing for safety? Like, if I wanted to run 93 when going racing, but 87 daily, would that be anywhere near something that's possible for an N/A build? *EDIT:* I should've watched the video before commenting, lol. Man, that's crazy to think about, though. I can theoretically run 87 in 12.5:1 with right mixture and timing, and I'll only lose a few % of power.

Based on the info in your other comment, cruise should be 13.5-ish. The open chamber heads, small cylinder pressure building cam profile and the moderate compression ratio will need to be just a hair richer than a more optimal setup.

Cam is quite small for your build. The problem with comparing old “advertised” duration numbers to new ones is the old numbers were highly inconsistent and given at .004”, .006”, and so on. Modern advertised numbers are mostly at .020”. When we compare cams it’s best to do so at .050” to get more comparable numbers. Your original cam is probably less that 210° at .050”. Ideally for a big block with a longer rod, you want to be in the 230s @.050” for around 10.5:1 compression range, 240s in the 11.5:1 range, 250s in the 12.5:1 range. Lift in all cases should make use of the head, so if it flows well at .200-.600, then you want to be around .580”-.620” lift to use that potential. I take a different approach to LSA and prefer a wider LSA, and I let the IVC event determine the ICL as a means of achieving a desirable effective compression ratio. As long as it pumps under 200psi at 200-250rpm it will run on pump gas.

No, if you use Lambda values to base the tuning on, Lambda 1.02 at idle with “1960s” 14.7:1 stoichiometric gasoline would be 15:1. With modern E10 14.2 stoichiometric gasoline, Lambda 1.02 is 14.4:1. It’s a seemingly “richer” air/fuel ratio, but only because stoichiometric ratio for the fuel is lower due to the oxygenation from the ethanol content. The combustion quality or completeness is the same, meaning, the emissions profile out the tailpipe is the same if not a little cleaner.

That it! You get it! It’s not bad fuel, it’s “different fuel” and if you use it correctly it works! Thanks for the comment!

@@TheGT350Garage Quick question, as I know each engine build is different, but is there a standardized A/F ratio for say 91 octane on a 10.5:1 vs say a 12:1 build? Or I imagine it's varied to a degree based on chambers and quench and pistons etc? What's the best way to determine your optimum A/F ratio in your driveway? Or does this have to be done on a dyno/at a tuner? Thanks for the VERY informative vids!

It’s relatives the same. The key is honesty to move away from A/F-Ratios to Lambda, at which point you’ll find 10.5-12.5 CR engines wanting 0.82-0.88 Lambda. The variation is typically less a factor of the compression ratio than the engine itself (chamber shape, quench area, spark plug location, tumble/swirl). Once the Lambda number is established, you can use it to switch between fuels like E10 to Ethanol-Free because Lambda stays relatively constant to the engine even when the stoichiometric ratio of the fuel changes.

@@TheGT350Garage Yeah, that's really cool. Flex fuel sensor could actually come in clutch for the right reasons! Now if only they had an octane sensor so you wouldn't have to manually change tunes for pump vs race gas.

Octane sensing is accomplished with a Knock Sensor. There used to be a kit that interfaced with the old Crane HI-6TR and instead of using a map sensor to retard timing for boost, it would retard timing when it sensed knock.

Here’s the thing with tuning the engine, we need to start with a conservative but realistic ignition timing value. So if we think the engine will take 28-30° TOTAL, we need to start with about 26° and then we can dial in the fuel. Ideally you’ll want to be around .85-.88 Lambda for your fuel selection to make peak torque and horsepower, don’t try to force an artificially flat air/fuel ratio across the range, peak torque should be a little richer than peak horsepower. Once we get the fuel right, then we can go back to the timing and incrementally increase the timing until we make absolute peak torque. That’s the limit, so we need to back it off 2° for street use. The engine needs to be a minimum of 180°F but I’ve found 200°F to be ideal for street use, it allows a 195° thermostat and you can manage the temperature with with the cooling system. Using a vacuum advance is actually the biggest help at this point because it does an incredible job of managing combustion temps at light to part throttle when it’s active. Spark plugs you want to run the coldest heat range that will still “self clean”. For example, with 12.2:1 compression I’ll be running an Autolite Racing AR3924 in warmer summer months and a regular Autolite 3923 spring and fall and a 3924 in the coldest months. As far as cam selection, it’s a little more complicated than I care to explain in the comments, understand I DO NOT use dynamic compression calculators to match the cam to the engine like most people will suggest, it’s bad science and not nearly as simple as that method implies. If you have a combination in mind and a power target, and you need a cam recommendation, shoot me specifics by email.

Your comment gave me a good laugh. Maybe you can convince Bert Kreischer to do car content on RU-vid.

Lambda is the best way to explain this, and metric volume and mass make it all easier to understand. 1hp requires ~0.563 grams per second of air. So if you have a 200hp engine it needs 112.6g/s of air. 400hp would need 225.2g/s, 600hp would need 337.8g/s. Lambda gives us better insight into the quality of the combustion process. Naturally aspirated engines can tolerate a leaner mixture and as a result lambda under maximum output will be .84-.88 where a turbocharged engine under a maximum of about 15psi boost will be .80-.84 Lambda. As boost pressure increases lambda changes very little, only about .02 for safety by 30psi. (Side note, you need to move more air volume at lower pressure to reduce heat and improve efficiency or you’ll need more fuel to cool the mixture down). Lambda is the air fuel ratio you need by multiplying it by the stoichiometric ratio of the fuel. So pump 91 is 14.1-14.2:1 these days, that means your target air fuel ratio is 11.3:1 on the rich end and 11.9:1 on the lean end under power. At 200hp you need 112.6g/s divided by 11.3 to arrive at 9.96g/s of fuel. The specific gravity of fuel is ~.74 so 9.96/.74 means 13.47mL/s or 808mL (0.808 Liters) of fuel per minute. Divided by the number of cylinders, and divided again by .80 you can get the injector size for 200hp. At 400hp you need 225.2g/s divided by 11.3 to arrive at 19.93g/s of fuel. The specific gravity of fuel remains ~.74 so 19.93/.74 means 26.93mL/s or 1615.9mL/m, 1.616 Liters of fuel per minute. Divided by the number of cylinders, and divided again by .80 you can get the injector size for 400hp. You’d run the same numbers for 600hp but be aware that as boot rises above 15psi so does the temperature of the air charge. Also, if you were using a centrifugal or positive displacement supercharger the numbers are different because you don’t see the parasitic losses to drive the supercharger in the flywheel horsepower. This is why Brake Specific Fuel Consumption (BSFC) on engine dyno tests is always higher on superchargers than turbocharged or naturally aspirated engines. An Eaton 2.3L TVS on a 2.0L engine would support 600hp with ease, but it will take 70-90hp through the belt drive to make the power, which means if you make 600HP with that supercharger you need enough fuel to support 670-690hp. Hope that answers your question.

@@TheGT350Garage it did more than just answer thanks. if you provide tunning lessons or whatever lessons to help increase knowledge in the auto world i would sign up

Shoot me an email to discuss consultation.

Dynamic compression is bullshit, I’m moving into a new garage and I’ll be back with a video using that as a title.

@@TheGT350Garage sounds great, looking forward to new videos.thanks for replies

As far as compression ratios with E85, if I was to build a dedicated E85 combination, because the fuel is less efficient, and also because it has a significant cooling effect on the combustion process, it would be a minimum of 12:1, and it could easily run as high as 14:1 and still be completely usable on the street. The drawbacks remain that E85 is not a consistent product in commercial form. Also at roughly 30% oxygen by weight it therefore requires roughly 1/3 more fuel by volume to make essentially the same power as pump gas or race gas. The fuel system has to be built accordingly, and if you’re using commercially available E85, you have to include an ethanol sensor in your fuel system or manually test every batch of fuel and adjust your tune accordingly. It’s not an “easy” or “cheap” option to run E85, and it’s not convenient. Building a combination that runs 91-93 octane fuel on the street makes more sense. If it’s purely a race car and your fuel comes from a can, E85’s advantages can be put to good use then.

Fuel is interesting stuff. It’s easy to think the octane rating has something to do with flame travel but it’s really just an indicator of ignitability the higher the octane the more stable it gets. Once it’s lit, 87 burns about the same speed as 91-93, 96-100, and 100+ octane fuels. Add to that the air in the cylinder is the limiting factor in the combustion process and the oxidizer that helps that fuel burn. The fuel was adjusted to the air the engine consumed and the timing is determined by the compression ratio, piston and chamber shapes, so once the air fuel ratio is optimized timing isn’t going to be much different regardless of the octane.

@@TheGT350Garage Cool, thank you for clarifying. So for gasoline it's about the same. I should have mentioned that I was thinking about ethanol vs. gasoline, not so much about the different octane ratings. That's why I imagine that there are effects at work e.g. charge cooling vs. fuel vaporizing, that cancel each other out to make a net 0 difference in this case. Like, if we look inside the chamber it might burn slower at a glance but there is less mixture in the ring land which would have taken longer to combust. So the optimum timing stays about the same.

@maikgoldmann5691 ethanol does have a cooling effect, and it carries 33% oxygen by weight, so as a fuel, it takes a lot more of it (thus the near +50% volume difference vs most gasoline blends) and even though you have more oxygen, because you have a larger total volume of fuel, the speed the fuel burns remains relatively constant to a given combustion chamber. I’m not a fan of pump E85 at all, it’s horribly inconsistent and you bad need to test every batch before using it to estimate the stoichiometric ratio and then adjust your tune accordingly. “Race E85” is at least consistent, but it’s nearly the cost of proper race gas. You actually get more benefit from installing a water/methanol injection system and running straight distilled water with pump 91-93 octane than you do from any version of E85, and if you want power gains, you can run up to 50% M-1 methanol (fuel) which will allow more timing and a slightly leaner fuel flow through the carburetor or injection system. Sadly, the perfect setup doesn’t exist in my experience, because that would mean having an ECM that monitors air/fuel ratio, EGT, Knock, and adjusts both the fuel injection and water meth injection actively and has protection against running out of water as well as the ability to progressively meter it against the tune.

If you go back to this video, it’s basically covered. You should know what race fuel you’re currently using and the race fuel should have a spec sheet. In the spec sheet, you’ll have information like the stoichiometric air/fuel ratio for your specific race fuel. Let me give you an example though. VP110 has a stoich point of 15.09:1, call it 15.1 for ease. That 15.1 is Lambda 1.00 for that fuel. If you. Had an engine tuned for 13.5:1 on VP110, you simply divide the air fuel ratio you tuned to by stoich to get the operating Lambda value. 13.5/15.1=0.894 or 0.89 Lambda. If you want to switch to pump fuel with a stoich point of 14.1, you multiply, so 14.1*0.89=12.55. Your new target air fuel ratio is 12.55:1. During the tuning process you’ll need to dial back the timing a few degrees and establish the new air fuel ratio, then add the timing back in. I’d suggest using an engine or chassis dyno to verify the tune, but data logging engine speed, air fuel ratio, and the time it takes to sweep an rpm range under full load also works.

I tuned a period correct 71 Challenger R/T with a 440 Six Pack for a guy a few years ago. The air fuel ratio was in the mid-12s timing was the key. Period correct engine with a purple cam through iron exhaust manifolds, with Vintage Air, it was running hot and the carbs were a mess when I started. A “stock” cam is the issue, you need a little more duration to help bring down the cylinder pressure. Very doable though, that car was making about 330hp at the wheels (400hp or so flywheel because it was a torque flight).

I don’t know the limitations of that engine in stock form so I really can’t speak to its ability to handle the cylinder pressure. Higher compression N/A engines typically have pistons designed to reduce weight, and the rings land are not usually very robust. Do your homework before you start modifying. Now, 10.5:1 compression with boost isn’t really a deal breaker, in fact it’s pretty common now. The new-ish Toyota T24A-FTS (11:1) and V35A-FTS (10.5:1) are perfect examples. Your J35A4 engine makes 240hp stock and should be 10:1 compression. You’ll see about 100hp at the tire from 7psi, about 145hp from 10psi, about 175hp from 12psi and about 200hp from 14psi. Keep in mind the effective compression ratio for 7psi is 14.8:1, 10psi is 16.8:1, 12psi is 18.2:1, and 14psi is 19.5:1. Your fully compressed cylinder pressure will be above 400psi at 14lbs of boost; that’s pushing the physical limits of the piston, rod, crank, block, head gasket, and head and main bolts pretty hard. Dropping the compression to 8.5:1 with rods and pistons brings that compressed cylinder pressure down under 350psi, and in the process you can improve the fasteners sealing capabilities, but that’s also the same pressure you’ll have at 10psi on the stock 10:1 compression ratio, so you have to do some research and find out when those engines will break.

With an FE, 11:1 is really not that bad, and 12.5:1 is possible, but you’ll need to do some things to make it work. Ideally, the flatter the piston the better, excluding your valve reliefs, avoid dishes or domes. I’d suggest Cometic gaskets for your bore size to reduce the volume of the gasket a little without having to give up piston to head clearance or sacrificing quench. The clambers on original iron castings are slow burn chambers and aren’t ideally efficient, but that doesn’t prevent you from using them with great success. Ported heads will improve your results, aluminum heads are a game changer and more ideal, but not necessary. Don’t get too conservative with the camshaft, and don’t buy into the old school cam company rhetoric about advanced cams and tight LSAs. You need duration in the 240s @ .050” which will give you a reasonable amount of overlap, and you’re looking for around a 110 LSA with a later (retarded) intake centerline around 112-114°, lift should be near .600” and valvetrain to match. If the budget allows I’d strongly recommend a hydraulic roller cam for ease of maintenance and reliability long term. Assuming you have adequate induction and exhaust for the desired power level from the combination you build, an 11-11.5:1 428CJ can make 500-550hp and turn 6500rpm with ease on pump fuel and be an incredibly fun and enjoyable, reliable combination.

Yes sir, like DV! Also, if you havn't already, you will certainly love Ben Alameda racing YT channel. He is really good and very knowledgable about this same kind of info and much more. Not taking anything away from Gt500 garage.

I have stuff in the works, life is complicated though, so I haven’t had time to get in the garage and do things the way I’d like to.

​@TheGT350Garage Understood. We came to the Philippines a couple of months ago. Working on house plans, getting the lot surveyed, and stuff like that. I am hoping, that when we go back to the states in March, that I can work on my 66 fastback some. Take care. Joe

You’re missing the key point of the video which is, the fuel isn’t what makes the power, it’s airflow limited. The various fuels across a wide range of octanes all produce essentially the same power for a given combination. That aluminum will allow a full ratio more compression is an old wives tale. It’s not the material making the difference as much as it’s the shape of the combustion chamber. Yes, iron retains more heat, but that’s just a matter of running a colder spark plug and altering the air fuel ratio to be slightly richer to keep the combustion temperature down. Back in the early 2000s I used to use quite a lot of World Products Windsor and Windsor Jr heads, later sold as Roush 200 and Roush 180 in both iron and aluminum, the reality of these heads being the same molds cast in two materials performance was essentially identical, timing was within a degree, the iron heads needed a little more fuel, as in 2 jet sizes on the primary side of a 650DP. I agree that engine would not have lived on 87, because it would be on the ragged edge, too lean and too much timing for 87 at that power level, but 91 was also far too lean in their test for safe street use, you’d need to pay attention to the lambda numbers I gave and dial it back to around .84-.86 Lambda to not have issues on the street, the dyno is a different animal, and they were posting “hero” numbers for the sake of views.

​@@TheGT350Garage all the fuels happy with the 29° and making the same power no matter what the octane was great to see and an eye opener for sure! It certainly backs up what your saying about todays fuel being better all around. Your point of today's 91 and 93 octane making numbers only dreamed of years ago is sure a valid one and they come with a factory warranty!! With a closed chamber and good quench with adequate fuel and sufficient cooling what would be the highest c.r. that you think could live on the street using 91 or 93 octane pump gas?... something that would be realistic? I'm looking forward to your future build ...any hints on specific numbers your thinking? The Shelby sure is a sweet ride is it close to the original powerplant? Any of your videos go into depth on the Shelby? Thanks for your work and patience.

I’m building a 12.2:1 compression 293” SBF. The car will be a pump gas only car. I’ve run as much as 13.5:1 on 91 before in DOHC EFI engines for open track use, its very doable. This will be a little more challenging being a carburetor, but no t a big deal, I’ll have to re-jet and adjust timing slightly when the car is at lower elevation for track days, but I’m not too concerned with a 15 minute adjustment. I will be running dual Lambda sensors to monitor the air fuel ratio, and that takes the guesswork out of it.

@@TheGT350Garage any lambda sensors and gauge you would recommend? With 2 sensors will they be 1 on each bank with a way to toggle back and forth with one reader or a sensor for each bank with a dedicated reader for each?

@jimhoward1655 Innovate DLG-1 52mm single 52mm (2-1/16”) gauge set up with sensor A on bank 1 (passenger side cyl 1-4) and sensor B on bank 2 (drivers side cyl 5-8)

Thanks!

Is there a closed chamber version of the same head? The quench area of a closed chamber works to your advantage and creates more turbulence at the top of the stroke as combustion is spreading giving a more complete burn. If you have enough camshaft for 11.5+ I would go that route.

@@TheGT350Garage no there’s isn’t Walter.? Only the open headed version. I already have the top of the ross piston above the block deck by .008. To further improve the mix. Right now I have only .035 of clearance from the top of the piston to the head surface. I don’t know how much closer I can go with piston rock. This is a new build and I haven’t bought the Kaufman heads but am specking them out.

The factory cam 288/302 had a 114 lsa vs this 106 and I wanted and the factory iron heads had an open chamber with 10.75 SCR so that was why I was inching up toward the 10.8. I’m wondering what my cranking compression would be. The valve events at .050 are IO 5* BTC and IC 37* ABDC, EO 37* and Eclose 5*.

@waltmucha2499 might want to go with a slightly thicker gasket being a big block, just to be safe from piston rock. The general consensus is .040”. On small blocks up to a 4.040” bore I’ll push the envelope to .030” with a flat top. With a dome I clay the edges of the dome during assembly to make sure the edges of the chamber maintain .030” to the dome. It’s a bit of extra work but quench is critical. The bigger the bore the greater the rock even if the clearance is the same as a smaller bore, so take the time to check it carefully and don’t sweat loosing a few thousandths of quench to a margin of safety.

@waltmucha2499 you’ll be close to 200

It’s been really challenging to make time for these videos this year. I do have more planned for this, and a lot of it is going to address questions I get regularly in comments. Thanks for watching, there will be more.

A cam that doesn’t focus on creating high cylinder pressure will often make more horsepower than torque. Of course that falls to the cam specs and the engine combination. Would be interested in a better overview of the combination including the cam specs and a look at the dyno sheet.

@@TheGT350Garage Do you have a mail address or a way I can mail you my dino sheet. Thanks Walter

@samuelerasmus7415 email address is in all the videos, TheGT350Garage@gmail.com

If it’s a closed chamber head with a dish you may want a little less initial and total timing. Open chamber with a dome to get that compression, you’re not far off. Idle air fuel ratio on a wideband should be in the mid 14s, the lambda value would be 1.02-1.03 at idle. Cruise will be lambda values in the 0.94-0.97 range. Under load, 0.84-0.88 lambda. If you’re using a wideband, read up on the instructions to determine how you can use lambda instead of the air fuel ratio, just keep in mind lambda has to be set up manually in some gauges/meters.

This is the thing about the heads I'm not to sure if they are open or closed chamber summit racing claimed that they can be both. Can that be? What I can say is the engine does have dome pistons.

@juanvelazquez6945 so, I wasn’t paying attention, at 115cc the heads are an open chamber, and even at over 500 cubic inches you have to run domes for that compression ratio. Domes impede the flame travel so a little more timing is required than a compact chamber with more quench area. For modern 91 pump gas, you’ll want to err to the richer side of things and target around .85 Lambda under load, right around 12:1 A/F, cruise A/F in the .95-.98 13.4-13.8:1 range, idle around 1.02-1.05 or 14.4-14.8:1, you can idle leaner if it will let you. Timing on a BBC with domes in open chambers will be low 30s under load, high 30s even low 40s with vacuum advance at cruise, and low to mid 20s at idle with vacuum advance.

Thanks a ton for your replies and information, much appreciated and keep up the great content.

I’m afraid you’re not going to like my response. I see no practical reason to build an N/A E85 engine for a performance application. It is undeniable that the engine will need 40% more fuel to operate at the same power level as an equivalent gasoline combination. I have tuned forced induction E85 combinations and where E85 has a small power advantage due to the roughly 33% oxygen content and cooling effect on the air/fuel charge, it still has a heavy penalty in terms of energy content per gallon and I’ve seen these cars with 14-16 gallon fuel tanks rendered trailer queens because they can’t make it to and from the track without refueling. If you aren’t equating BTUs to moving the crankshaft then you don’t understand how an internal combustion engine works. Ethanol has as a lower BTU (energy) content because it’s carrying a bonded oxygen molecule where it need’s hydrogen and carbon to produce more heat. The flatter expansion rate you’re referring to is because it burns slower and takes longer to release its energy. It can release more energy from a richer stoichiometric ratio because of its oxygen content, but it still means more fuel, not less, and than means any talk of “efficiency” is moot because where we’re looking for the most power or distance from the least volume or mass gasoline beats ethanol every time. This is proven by the specific gravity of the respective fuels and their stoichiometric ratios. Bringing top fuel (methanol and nitromethane with an even lower energy density or BTU content, not to be confused with ethonol), and diesel into the discussion don’t help your point. It takes converting the stored energy content in those fuels into heat that produces pressure to rotate crankshafts too. The lower the energy content of the fuel, the more fuel required to produce power. Period. Can Nitromethane with its 1.7:1 Stoich make more power than gasoline? Of course, but be it by mass or volume, you’re going to use a hell of a lot more of it to do so. And as far as your comment about burning fuel by mass and not volume, you’re right, but take into account that an engine will only consume the air it can consume for any given speed and throttle opening. Air weighs 1.23grams/liter. Any naturally aspirated 4-stroke engine consumes a maximum of 1/2 it’s displacement per crankshaft revolution at 100% efficiency. So a 6.0L engine could consume 3.69g of air per revolution, at 6000rpm that’s 22,140g. E10 gasoline (14.1 stoich) weighs 745gram/liter, at .85 Lambda (13.25:1) you need about 1670g of fuel, just shy of 2-1/4 liters per minute. E85 gasoline (9.8 stoich) weighs 790gram/liter, at .85 Lambda (8.33:1) you need about 2658g of fuel, just over of 3-1/3 liters per minute. There’s your mass and volume calculation. Now, are you ready for this, E85 is about 20,100 BTU per liter vs 30,400 BTU for gasoline. So 3-1/3 liters of E85 is about 66,900BTUs and 2-1/4 liters of gasoline is about 68,400BTUs. If I were being more precise and not rounding those numbers would be nearly identical. You need to learn more about how your engine produces power, how energy is released from fuel, and don’t try quite so hard to prove a guy wrong who has spent 35 years working in the industry doing performance tuning, is an expert in engine and drivetrain control systems, emissions control systems, and drivability diagnostics. The math and science behind engine performance doesn’t lie, but the schmucks on the forums and elsewhere on social media do. I put months of research and writing into this video, this isn’t some regurgitated Wiki article, forum post, or something I dug up from someone else’s work.

If you install a Wideband air/fuel ratio sensor in the header collector or the mid-pipe after the header collector, the sensor will read all cylinders on that bank. What you see from a single sensor is the average for the cylinders being monitored. To get individual cylinder data requires placing a sensor in each exhaust primary tube. Since this isn’t practical, it’s usually easier to install EGT Exhaust Gas Temperature pyrometer probes in the header tubes. EGTs can help you identify cylinder to cylinder mixture distribution problems and optimize the engines ignition timing.

@@TheGT350Garage then in theory the number 2 cylinders should be ok if I showing 12.5 on the gauge this motor is a chevy thank you for the informantiom.

@markbogle8062 so, if 2-4-6-8 were 13.5-11.5-12.5-12.5, the average would be 12.5 even though 2 is lean and 4 is rich. Checking the plugs during tuning would identify lean and rich cylinders. Ideally if all the stark plugs appear similar you should be in good shape. But taking a 4-cylinder average and saying everything is fine with out checking plugs at the minimum would be foolish.

Thank you very much for this information

It really goes back to the change from RON to AKI (R+M)/2 octane ratings. People were used to much bigger octane numbers and they just assumed the new numbers were inferior octane values because they were less than the old numbers. The addition of MTBE and later Ethanol to oxygenate the fuel contributed to the misconception that the fuel was “watered down” and increasingly inferior.

@@TheGT350Garage so from my understanding of this,, the 385" botie I've built with 13.7 slugs in it can be run on 93 octane?. My cam is 110° LS 615/625 around 265 duration if I rember right with cast iron wp heads..64ccangle plug/no power adders .and I'm regressing my piston choice since I started learning more about quench area..what are some of the finer things I should consider to help make this work.i have mixed 93 and 110 50/50 with no problems

You just need to remember that the more compression you run, the more reactive the compressed air/fuel mixture becomes. If you are truly at 13.7:1 CR, you’ll need to treat the engine a bit more like a forced induction application and you will not be using as much timing advance because the A/F mixture will react (combust) faster. I would also recommend running a richer A/F ratio based on a Lambda number in the range 0.800 to 0.825, so with E10 93-octane, you’d want the AFR in the 11.3-11.6 range initially while finding the ideal timing and then lean the engine a bit to get in the .825-.850 lambda range (11.6-11.9:1 AFR). It sounds extreme but it’s not really. If you had a 9:1 engine with 7.5psi of boost, you’d be equivalent to 13.5:1 compression, and no one thinks twice about such a basic setup these days, the A/F ratios would be similar and the timing would be 6-8° less than a 9:1 engine will tolerate N/A, high compression isn’t much different, you just have 50% less airflow so you’ll consume about 50% less fuel than a supercharged engine would. The tuning aspects are relatively the same though because the cylinder pressures are incredibly similar, as is the reactivity of the mixture by the same reason. It be area you actually have an advantage over an S/C combination is you’re running more cam so you scavenge better and have less overall heat in the chamber.

@@TheGT350Garage the guy at my local machine shop says he thinks the ratio should be at least over 13 to 1 which sound about right with a .043 squished gasket.and .010 off the heads is hardly a hurtful amount.my cylinder pressure is around 205psi.my prior 12.4 pistons (when it was355) was about 185...the tq I gained was quite noticable once I up'd the stroke and comp Wish there was affordable gas that was about 100 octane. I could learn to like that .also found out that staying away from aviation fuel is wise .due to the mixture and elevation it's used at

If you have ethanol free fuel available to you, you’re going to want to target about .85 Lambda as your starting point. Since your fuel is 14.7:1 (14.7*0.85=12.5) 12.5:1 is you target to start with. I would not advise going over 0.90 Lambda. So your “lean limit” would be 13.2:1 (14.7*0.90=13.2). If those numbers feel very “old school” they are. That’s near the air/fuel ratios the muscle cars ran in the late ‘60s to early ‘70s, and that’s in the range of what dyno articles used for pump gas through the e bd of the ‘90s. Target the richer end of the scale initially and remove fuel, watch torque in the mid-range and horsepower up top using a dyno. In just a couple hours at a dyno you can dial in the jetting and be very close to ideal, then swing the timing over the course of a few pulls to find peak torque and horsepower, back it off 2° at the torque peak and it will run like you want it to. On the street, find somewhere safe that you can run the car through 2nd or 3rd gear and sweep the rpm range you are tuning 3 times exactly the same way and record your results. You’ll need a wideband A/F gauge and a stop watch or accelerometer. Set the timing about 6-8° less than what you think the ideal total timing would be. Get the target A/F set so the car is repeatable at 12.5:1. Then start conservatively and adjust the timing 2° advanced at a time until the car slows down. Back the timing off 4° in this case, that will make it safe and leave 2° on the table for track use. Go back to the fuel and jet down a little targeting 12.8:1. If the car gains, you need to swing the timing 2° advance and retard and look for a gain or loss. Repeat the process with a target of 13:1, then 13.2:1. Any time the car slows go back to the previous best, always leaving 2° of timing on the table for a margin of safety. That’s how you do a street tune.

@@TheGT350Garage So the 12.5 - 13.2 is what i should be targeting at WOT? With my Idling AFR should that be no leaner then 13.2 AFR? I have a Fitech Throttle Body Fuel injection and can setup and tune my AFR fairly easy. I'm currently dealing with a ping at idle and I'm wondering if I'm just trying to run it to lean at 14.2 AFR, but with adding fuel to the 13.2 AFR you suggested would that cool the cylinder and get rid of the ping in the process? It only pings if I let it is up to operating temp and I get out after a drive and open the hood I can hear the intermittent ping. Thank you for your quick response really appreciate it.

At idle you should be around 14.8-15.0:1 with EFI. Check your timing with a timing light at idle and verify you’re in the high teens to low 20s, don’t trust the ECM exclusively.

@@TheGT350Garage So you would suggest raising AFR to within that range and then adjusting timing for best Idle? Once again thanks for your input. Live in MN and wrapping my head around some new Ideas for when I pull my 69 Camaro back out of storage so i can hit the ground running.

As a general set of “ranges”: Idle should be 14.6-15.2 AFR, 10-26° BTDC Cruise should be 13.2-14.6 AFR, 26-46° BTDC WOT should be 12.5-13.2 AFR, 26-36° BTDC Every engine is different. Every combination is different. So those are generalizations of what your engine “might” run. Remember, cold start requires additional enrichment. Don’t set the AFR or timing if the engine is not up to operating temperatures. Fine tuning everything will result in finalized numbers somewhere well within those AFR and timing ranges.

It’s ok, if I gave you instructions on how to use a timing light you wouldn’t follow them any way.