Breaking down compression ratio on our 4.6L Jeep

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Grab a seat and pull out your notebook because class is in session. This week Davin dives into compression ratio on our 1993 4.6L Jeep XJ engine. It's not an overly complicated process to calculate what the ratio of an engine is, but there are a few things that can trip you up. So, join us as Davin breaks down some of his tricks to make sure you've got all the numbers you need.
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6 мар 2022

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Комментарии : 132

@kevinphillips8953 2 года назад

Thanks for the shout out to my auto shop classes Davin. We really enjoy and appreciate the correct information. You should have seen the look on their faces when you mentioned us by name. A few thought that I had somehow manipulated the video. It was a great day in the shop.

@renc3920 2 года назад

Relatively speaking, this was a relatively great compression ratio lesson. I'm relatively impressed and sure my relatives will be as well. :)

@isaacjanness7897 2 года назад

Really happy to see you guys working on a 4.0! The Redline Rebuilds series inspired me to do my first engine build, so this past summer I built one up for my 99 cherokee sport. Love the vids and keep up the great work!

@MAtogable 2 года назад

I came here for a greasy rebuild, I left with a PhD in applied Physics Good direction you are taking with this! Is different and I like it.

@seahorse5677 2 года назад

Well this is gonna be an extremely helpful video for years to come

@improvisewitme 2 года назад

This is well beyond my comprehension. Great vid and I very much enjoyed this.

@PrairieDad 2 года назад

This project series has been absolutely great. Keep them coming!

@Mrcaffinebean 2 года назад

I love that you guys cover the “thinking” side of engine builds. So many build videos are just guys spinning wrenches. But this stuff is what truly makes an expert

@MikeGuy993 2 года назад

Really enjoying the series, and you guys always have great music to go along with your videos. Always the right vibe!

@robertkocarmotorsport 2 года назад

I must say that this series brings lots of useful informations. Keep them coming. :)

@crxtodd16 2 года назад

Outstanding work, sir. Thank you for breaking this down for us plebs. I've built a few engines, mixed and matched stuff; but, luckily for me all the measurements were available via a few different online compression calculators. Said calculators are very helpful, but sometimes you gotta customize a few things... I've never dared to used a buret, nor really understood how. Your demonstration clears up a lot of questions I had. Nice!

@13slot28 2 года назад

Best series on YT, hands down!

@losergamer04 2 года назад

I am loving this series. My dream garage is a Miata with an LS3 and a Cherokee (XJ) with a stroked 4.6L engine. You're literally building my dream Jeep. Some day I hope to follow every video as I build one in real life.

@blurglide 2 года назад

I'm the guy who ran the numbers in the last video. Didn't realize your pistons were dished

@970357ers 2 года назад

It's funny how real engine building is a process of experience, attention to detail, patience yet TV shows it as one of high-jinks, smashing stuff and throw it together.

@giancarlopbranco 2 года назад

That's awesome job, professor! Thank's to share knowledge!

@johnnyk617 2 года назад

Goddamn love this channel I've been rebuilding engines for over a decade but I still love seeing these explanations

@stevenrey56 2 года назад

Yay! Sequim mention! Interesting as always guys.

@j3rocketeer 2 года назад

I really like the shout out to the high school class. We need the fresh blood in the industry

@jeffplant3 2 года назад

Love the math. So key to having a successful result. Not doing it would be a disaster in the end. Well done. Love these videos. Science/Physics, it's all so important. Cheers from Toronto!

@autka_me 2 года назад

No 'get to the shop, get your work done' today? I guess I'll have to just sit here.

@christinewhybrow8813 2 года назад

Wow, I've not done physics like this since uni. I hated it then, but actually enjoyed following along here. Always love these videos, with or without math!

@BuffMyRadius 2 года назад

I saw that 8.49:1 and my immediate thought was "thems turbo numbers!"

@nilejuneau1972 2 года назад

Just orders a strocker kit for my 4.0 thanks for this vidio im realy going to enjoy this build cant wait for parts to show up

@outfitsgarage88 2 года назад

Great lesson

@ellieprice363 2 года назад

Thanks, what a great math lesson. I’ve always wondered how that was done and now I know.

@ACommenterOnYouTube 2 года назад

Great video 👍🏾

@mattaarts122 2 года назад

A great follow up to this (especially now you are decking the block) would be how to measure/calculate piston to valve clearance. Love the series, keep up the great work.

@av8tore71 2 года назад

You should be an instructor at a college somewhere and teach younger generation who is starting out. I'm an A&P mechanic working on people's airplanes and this is the same math when working on Lycoming and Continental aircraft engines. We done have heads but individual JUGS or cylinders 4 to 6 per engine. 2 spark plugs per JUG or cylinder

@retiredafce3373 2 года назад

Good teaching video!

@mattgraham1983 2 года назад

Wow the box for the pistons said 22.x cc but worked out to be 27.x cc..... definitely always pays to check especially when you are creating a Frankenstein engine

@dirkmohrmann8960 2 года назад

Similar issue with domed pistons. I have the feeling that some manufacturers measure or calculate the volume for a certain size piston, and then print that same number on the box of all the sizes they make.

@davidmiller9485 2 года назад

@@dirkmohrmann8960 what's more likely is they average it out. They measure a set number from a run of pistons then average that out.

@alexneilson598 2 года назад

Engineering tolerances apply in every direction so depth, diameter both deck surface and bottom surface and the relative angle of the taper all have an allowable tolerance which is a percentage of the overall dimension. As the checks are measuring in volume of the vessel, which is a different way it is quite easy for the part to be within engineering tolerance in terms of measurements but a long way from target volume in this type of test. That’s for the part, also sometimes it’s fun to flip your plastic over and try it the other way, this will prove if your plastic is flat. LOL.

@jimt9661 2 года назад

there is also going to be some slight variation in measurement. For example, doing it ringless with grease at the top of the piston will not include the area between the top of the piston and the top of the ring. Depending on piston/bore clearance, this could add a few CC's

@Kwqr_1996 2 года назад

Good job!!!

@jamesdiehl8690 2 года назад

I'm so glad you cleared all of that comp ratio math up! Now I can take a long leap ahead and figure out what size of rubber band I need to roll up a newspaper. Look out Einstein, I'm after you! 🤣 😂 😆 🤣

@grad0n 2 года назад

I built my 4.6 back in 2008. I used the 4.2 rods, sealed power h825cp30 pistons with 17.5cc dishes, and a mopar p45292230ab cam. It was 9.5:1 scr and 8:1 dcr and I had to use 93 octane. I spent over 20 hours porting and polishing the head. It went in a 96 2dr 2wd 5-speed SE(all manual base model) that I stripped down to 2700#. It ate through 3 auburn lsds. It made many smiles and got questions about it having a v-8. I will build another with the Eagle 6.150” rods I’ve been hoarding and some custom +.080” pistons to get a 4.8l and will go in my 99 2dr 4wd 5-sp with a np242(full time option) and eaton rear(no more clutch wear!).

@StrapMerf 2 года назад

List of things I did not expect to see in a car/engine channel video.... Burette, haven't seen one of those since yr 12 chemistry

@PouyaEmami 2 года назад

Always great to learn while watching your content! One question I have: Is there a reason why these calculations couldn't have been done before sending the engine to the machine shop the first time around?

@autka_me 2 года назад

Both head and block were machined, sometimes it's hard to say how much you have to shave to make them flat and clean.

@PouyaEmami 2 года назад

@@autka_me Thanks for the quick response!

@R_o_b_e_r_t 2 года назад

I mean, for me its logic. The way you asked is like asking why cant I put primer on before I (for example) degrease the engine?

@scottimusgarrett15 2 года назад

Excellent video, showing how you can't just huck an engine together in 15 minutes!✌️❤️🙂🇨🇦

@tompyle5438 2 года назад

Very cool.

@peninsulahomerenovations9680 2 года назад

I graduated from Sequim high and let me tell you I got a kick out of that ending. Mr. Hammel was the auto teacher when I was there.

@Deuce1550 2 года назад

Yes coolant is easier to see, but the real advantage is the lower surface tension of coolant compared to water. Keep up the great videos Davin and team.

@ellieprice363 2 года назад

Red transmission fluid would also work well with a good contrast.

@NunyaBSniss-py1oz 2 года назад

More!!!

@SupermasiveHole 2 года назад

Muy bueno…como siempre

@803mastiff9 2 года назад

One day, Thomas Edison passed a light bulb to his research assistant, Upton, who was a graduate in Mathematics from Princeton University. Edison asked him to calculate the volume of the light bulb. So, Upton picked up the light bulb and stared at it for a long time. He then used a measuring tape to measure the light bulb and did a lot of calculations too. However, he still could not find the volume of the light bulb. Edison saw this poor guy and said: ‘Upton, why don’t you try this method?’ He filled the light bulb with water until it was full and passed it to Upton saying: ‘You can find the volume of the light bulb using a measuring cylinder to measure the volume of water.’

@giannirocco7492 2 года назад

Thought this one of the better episodes...

@raymondparks4108 2 года назад

David this will be a perfect build. 200 to 225hp, but a very big improvement in torque. Torque the most useful in Jeeps and trucks.

@T0tenkampf 2 года назад

If ya REALLY wanna be retentive in your CR measurement then you have to install the compression ring to include the volume around the shoulder of the skirt above the top ring.

@jimt9661 2 года назад

So, I didn't redo the math, but I think if the crank wasn't ground yet, you could spec a .010 offset (stroke increase) and it should bump the C/R to about where you want it. It would give you an additional .020 to the stroke, and decrease the total combustion area by the .010 stroke. Might be more cost effective than re-decking the block. especially when the block has already been cleaned, prepped and painted.

@3210gatorbite 2 года назад

Jeez David, it sounds like you're having a stroke near the end there. Lol

@catlee8064 2 года назад

Could you do the head aswell? Dished piston will make sure your valves have clearance.

@matiasdamian8106 2 года назад

Thank you Davin for share your knowledge and taking the time to explain this things, I have a chevy 230ci straight six, and time ago i wanted to make it more efficient by increasing the CR, in theory this engine stock had between 7 to 7.5 to 1 CR, which for and gasoline engine, it's so bad haha, and for street use only i wanted to do the same thing you're doing here, the only difference is, here if i use the AKI standard, RON+MON/2 method the "cheapest" fuel i can get in my country is 89.5 octane, so with that little more than 87 how much higher could my compressión be? Up to 10 to 1 maybe?

@revolutionday1 2 года назад

"Oh boy, more math!" *groan*

@ZeGermanHam 2 года назад

I'm just glad that I don't have to do math in front of a camera for an audience of many thousands. 🙂

@martinrezzy 2 года назад

VERY useful video...thank you very much..i want to stroke my engine some day and this was the info i was searching for...i need to find some more info and i will be fine...i hope..the only problem i am worried about is the cylinder head...can i put bigger valves from the 2.8liter engine on my 2.0?i want to give it enough air...i will ask the guys in the machine shop if they can make it,but still if someone had done it i will be glad to hear it...thanks again..i love these professional explanation videos very much...i am still amazed how helpful the internet is...sometimes :)

@bigtony7451 2 года назад

I don’t understand, why wouldn’t you just go with flat top pistons?

@mattgraham1983 2 года назад

Probably availability in said diameter and cost, keep in mind this is going to be a street car

@Hagerty 2 года назад

Availability

@timcouch2037 2 года назад

Can you talk about quench in the next video? If i heard correctly you will have .062 of quench, which i dont think counts. Would it be better to have a little more compression and quench in the .045 range? I just did this on my 4.0 and it turned out great.

@RC-cf7yu 2 года назад

I enjoy watching your videos, entertaining ang informative. Could you include also the titles of back ground music in the time lapse. Filipino subscriber in The sunny Republic Of Maldives.🇵🇭

@paulkoontz6095 2 года назад

I just wish I could find someone who rebuilds engine's around me, Id like to have my son's jeep rebuilt. Hard to find here in my local vicinity in Pa

@kolbaska19 2 года назад

#1 car addicted

@marcusFZ6 2 года назад

Compression Ratio -I really enjoyed your detailed explanation of it all - did a killer job. Q: Why 9 to 9.5 for running on your 87 Octance??? Why not bump up higher to get a better & faster burn especially for the lower octances?????

@dennisp.2147 2 года назад

Detonation.

@marcusFZ6 2 года назад

@@dennisp.2147 You would think that lower octane fuel would burn better with a higher CR & not detonate too early.

@dennisp.2147 2 года назад

@@marcusFZ6 You would be wrong. The octane is there to reduce detonation and pinging at high compression.

@MrJacksjb 2 года назад

@@marcusFZ6 The purpose of higher octane is to run higher compression ratio. There's no appreciable difference in the energy from burning low vs high octane fuel. High octane allows higher compression ratio which is the reason it is required in higher horsepower engines. On a side note, E85 ethanol added fuel is really above 100 octane due to the alcohol. A lot of hot rodders and racers build dedicated E85 fuel engines that run really high compression.

@T0tenkampf 2 года назад

@@MrJacksjb I have been told that E85 equates to about 107 octane in terms of flame quench...sound about right? Its actually a liquid intercooler when you have boost.

@johnnysamples 2 года назад

I may be splitting hairs, but do you factor piston to cylinder wall space above the top ring?

@rogjackson 2 года назад

You'd have to do math if Davin taught auto shop.

@Ioughtaknowbetter 2 года назад

So I just wondered why not go to a piston with a flatter head? Is the dished head piston that much of a performance Improvement?

@av8tore71 2 года назад

I usually run 100LL AVGAS in my Chevelle but at $7.50 per gallon it's getting very expensive and with a 427 it drinks A LOT!!

@leviathan5207 2 года назад

Why? How high is the compression and/or the heat that 102 Ultimate (90MOZ) would not do the job?

@catlee8064 2 года назад

Im paying £8 per gallon....$11/$12....

@moparedtn 2 года назад

Such animals are probably not practical/available, but would it be any better to have started with a "zero deck" piston in this circumstance?

@TML34 2 года назад

How do you know how much the gasket compresses?

@dirkmohrmann8960 2 года назад

It'll tell you in the specs for the head gasket you buy

@19504x4 2 года назад

Volume of a cylinder is pi × r squared x height. I don't know where you got your formula for the head gasket.

@michaelcress8767 2 года назад

I think you should build a 2.5 4cyl

@ianatkinson8464 2 года назад

😎👍

@billbeyer657 2 года назад

Any of you "geniuses" ever heard of the formula pi r squared as in pi x the radius of the circle squared? A lot easier to remember than pi/4 x diameter squared.

@ellieprice363 2 года назад

Diameter squared x .7854 x stroke = cylinder volume.

@jtdyalEngineer 2 года назад

Fantastic episode! Fact that your figures came that far off of what you thought they would be has me thinking I should check mine before I assemble. Thank you Do you only ever use static compression? Or do you only consider dynamic compression on high performance motors?

@Noboundries85 2 года назад

Trust but verify!!

@Josh-ce9sv 2 года назад

Sooo....not changing the cam? Because you didn't mention static compression VS dynamic compression. Bigger cam = less compression.

@loganabrell6929 2 года назад

hey i love your videos but i live in west terra haute indiana and tgere are some nice cars and they were in a junk yard and they closed down but they are there and you should check them out sometime

@muntasirgourab1484 2 года назад

That was a Math class

@streetfighterracing1583 2 года назад

Less dish of a piston?

@Alex_Miller1980 2 года назад

Next time I'll skim some material from the head of my scooter it's an 8.9:1 I'm good under 10.0:1 regular gas gain some little power here and there

@terrymillard9255 2 года назад

Forgot the ring land

@islandaerial3414 2 года назад

From a 4.0L to a 4.6L using Imperial measurements? 🤔

@ellieprice363 2 года назад

Why not? It’s an American engine and was built using Imperial measurements. Convert Devins numbers to metric and do your own calculations.

@user-bi7xd8ry5p 2 года назад

@@ellieprice363 US manufacturers have been using the metric system for decades now. That's one of the reasons that engine displacement is given in liters or cubic centimeters instead of cubic inches, even in the US.

@ellieprice363 2 года назад

@@user-bi7xd8ry5p True, but most older American mechanics still think and work in the inch system Just because Imperial is not easily understood doesn’t make it obsolete. The engine is still the same size no matter how you measure it.

@HaythamBuKhadra 2 года назад

Notification squad

@thefixerofbrokenstuff 2 года назад

It's a shame you didn't just have the right pistons.

@rickwhitmire7933 2 года назад

The more you know…

@monkeybarmonkeyman 2 года назад

Me thinks you been cheating yourself on sleep recently? Hope I'm wrong. Since you're shaving the deck on the block, how much can you take without causing issues in the valvetrain? Myself, I'd prefer a cutdown that would allow me to use a standard head gasket so the next owner, should they ever have to replace the head or remove it, wouldn't get caught short. Does that make any sense?

@starsundsternchen802 2 года назад

When you use metric units, please do it right. In this case, for the volume it should be "ccm" (instead of only"cc")!

@ladam836 2 года назад

Why engine manufacturer said cc on their tech info?

@starsundsternchen802 2 года назад

@@ladam836 Perhaps the are clueless!? "ccm" stands for "cubic centimeter". The "m" is therefore essential!

@scotte2815 2 года назад

GGRRRRaaAAARRRGGGHHHHHH!!!!!!! MY HEAD HURTS! area of a circle is found with pi times the square of the radius. if, IF you are working with diameter then it's pi times (D/2)squared. You GREATLY complicated it. So much so that I couldn't follow your math. If this was a classroom, I would not care that you got the correct outcome. I would have failed you on process! The laughable thing is that it's even easier with a 4 inch circle. Radius is 2 inches, when you square 2 you get right back to 4, so, pi times 4

@lostcabrio 2 года назад

Oh muricans, go metric! Then you don’t have to convert to cc’s…

@JyveKilla 2 года назад

Dear America. the math is easier in millimetres so buy some metric measuring tools if you're doing this.

@ellieprice363 2 года назад

Why? Just to please a few viewers who’re unwilling to do their own converting. When you watch a free American video don’t expect the producer to do your work for you.

@JyveKilla 2 года назад

@@ellieprice363 you know every other country in the world uses metric. Also the final answer he wants in metric (notice it wasn't in cubic inches?) So why start in inches. I also said it's easier, not that it didn't please me. Are you going to complain he didn't do the capacities in cubic inches because it's an American video and should have used American units.

@ellieprice363 2 года назад

@@JyveKilla No, I’m not complaining about anything. Just enjoy the video for the value it provides. Expecting the whole world to switch to metric for the pleasure of a few viewers is not going to happen. Get over it. No more from me on this subject.

@JyveKilla 2 года назад

@@ellieprice363 you need to read what I wrote... The math is easier in millimetres is all I said. Oh I think you don't realise that cc and litres are metric units.

@JyveKilla 2 года назад

@@ellieprice363 also, the whole world IS METRIC! America is on its own.

@SpatialDragon 2 года назад

Acid brush and then use your finger anyways. LOL I am not sure about your theory about the in the engine to measure the dish being better, but it does work your way. 9.25 is not bad. Maybe less dish and do your math earlier would have been a better idea, but with Joe Biden as President it may not matter since we won't have any gasoline to burn anyways.

@batiusfinkius2923 2 года назад

Measures everything in inches, then has to convert to centimetres to get to CC…Could have just saved a whole heap of maths just measuring it in centimetres directly 🤷

@thefixerofbrokenstuff 2 года назад

16.387 is not a lot of math.

@R.S.R.S. 2 года назад

Why are you mixing metric with imperial? I don't get it, making every single move a complicated story.

@itsyourAGS 2 года назад

9th liker and 3rd comment 😉😎

@ACommenterOnYouTube 2 года назад

1st 👍🏾

@Zura_Lanch 2 года назад

UKRAINIANS NEED HELP!

@boostkash2640 2 года назад

Bolt head on block , piston on tdc , pour fluid through spark plug hole and finished. No need to waste time on a stupid video.

@ClaytonYatescarenthusiast 2 года назад

Really misleading. Lot missing here. First being the ratio for pump gas. Completely irrelevant. Direct injection. Cooling capacity. Air to fuel, turbo non turbo, variable cam timing, the list is long. A 14:1 car will run on 87 octane with less aggressive timing and the right cam that reduces dynamic compression. So far off here