Engine Displacement - Cylinder Boring for New Pistons

Myx

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To upgrade my stock pistons to JE Pistons, a shop had to increase the cylinder size for the new pistons. I don't have the exact numbers but looking at JE Pistons site --> HERE, it shows two different piston sizes. One is 2.874 and 2.894. So if you increase your cylinder size to put in pistons that are .02 wider, how much does this increase your engine's displacement?

Just curious! Even if it is a very small number, I'm interested in knowing what that number (increase) in displacement is. Thanks!





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Stock bore and stroke is 73mmx89.5mm which gives you 375cc per cylinder (x4 = 1500cc).

Boring out by that .02 inches gives you 73.508mmx89.5mm which gives you 380cc per cylinder (x4 = 1520cc).

So overall a 1.33% increase in displacement
 

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Stock bore is 2.87”, displacement at 1497cc. The displacement at 2.894” would be about 1517cc
 
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Stock bore and stroke is 73mmx89.5mm which gives you 375cc per cylinder (x4 = 1500cc).

Boring out by that .02 inches gives you 73.508mmx89.5mm which gives you 380cc per cylinder (x4 = 1520cc).

So overall a 1.33% increase in displacement
Stock bore is 2.87”, displacement at 1497cc. The displacement at 2.894” would be about 1517cc


Big thanks for the quick replys guys.
So in theory.....could this mean a possible 1.33% increase in horsepower/torque?
 

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Big thanks for the quick replys guys.
So in theory.....could this mean a possible 1.33% increase in horsepower/torque?
I can calculate the volume of a cylinder but that's where my experience ends lol. I'm sure increasing displacement improves power but whether its 1:1, no idea.
 
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I can calculate the volume of a cylinder but that's where my experience ends lol. I'm sure increasing displacement improves power but whether its 1:1, no idea.
I am a simple-minded person. So was just thinking that since cylinder capacity has increased by 1.33% that it can intake 1.33% more air volume, which should use 1.33% more fuel and make 1.33% more hp/tq. I'm sure it's not exact but it's just wishful thinking. The calculation is good enough though. Really appreciate it.
 

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I am a simple-minded person. So was just thinking that since cylinder capacity has increased by 1.33% that it can intake 1.33% more air volume, which should use 1.33% more fuel and make 1.33% more hp/tq. I'm sure it's not exact but it's just wishful thinking. The calculation is good enough though. Really appreciate it.
Sorry to hear about your motor btw. Looking forward to seeing what you end up with!
 
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I’ve had .25 bigger pistons in my h22 when I refreshed it, it did not do anything. It’s so small a difference. In theory yes the cylinder are wider but it’s very neglible. It’s just to have a smooth cylinder wall surface. On a side note I would like to see more on this topic. Once people start to really bore out these blocks and throw in bigger cams, we’ll start seeing much bigger builds without meth, c16 ect.
 
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Oddwayne

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1.33% whoopdefuckindoo

How could this possibly be worth your money and time?
Sometimes when you rebuild your block the cylinder walls have scarring. If they are deep, like enough that your finger nail can catch on the scratch, you gotta hone your block a bit so the rings seal like they should and so you don’t mess the rings or skirts of the piston up. Lots of engines are like this. There’s standard bore and oversized bore, which really isn’t much bigger.
 
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Sorry to hear about your motor btw. Looking forward to seeing what you end up with!
Thanks for the kind words. This was a long time coming as I have been doing crazy-risky stuff for WAY too long on other platforms and getting away with it (Ex: Running turbo & nitrous on stock blocks with no issues).




1.33% whoopdefuckindoo
How could this possibly be worth your money and time?
For power itself, it's not worth it. Upgrading my pistons/rods to avoid having problems with them in the future. Not recommending anyone do this for horsepower purposes. Just was curious on any potential impact the wider cylinder has on power.

Also, I do a bunch of tiny potential power additions that are all small by themselves but stacked have an overall impact. So this (for me personally) is HUGE. I don't make a lot of horsepower now as is (Stock turbo, CVT, no ethanol). Despite not having ethanol or a bigger turbo, I can still hold my own from point A-B against those that do 'whats worth it'. It's not because I only do the things that are 'worth it' but I pay attention to all the little stuff that isn't worth it and try to build on them.

One example of this is my testing 100 octane on a tune customized for 92 octane. People generally say it's not worth it and you will not make hp/tq adding high octane unless you are tuned for it. Well, I added it at the track and consistently ran 1-1.5mph faster than all my other previous times. And I tested this twice. Is it worth it? I don't say whether it is or not. I just do things and post the results.
 
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charleswrivers

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You can conceive the the greater the surface area on the top of a piston... then greater the torque. Tiny differences yield tiny results.

The use of thin (low resistance) rings can have a pretty measurable effect. It’s one of the things that is a regulated standard in NASCAR. The thinner the rings... the more blow by you can get... so there’s going to be a compromise for emissions and for durability I’d expect on a OEM engine. If you’re building your own... it might actually be something you’d have room to work with if you were looking for a screamer. I wouldn’t go thin personally on something you wouldn’t be willing to do it all again with what is essentially a high compression (because DI allows it since it’s less detonation prone) turbo engine.
 
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builders use next size up/oversized piston to restore bore condition, not to gain displacement. Stock bore pistons are fine if your builder says the bores are in good shape. You usually want a looser PTW with forged so a hone could be all thats needed if your block is in decent shape. Any cylinder work needs a deck plate/bore plate when working with open deck sleeves. Top end will move around a mesurable distance when you torque your head down.
 
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The correct answer is:
about 21 cc increase in displacement relative to nominal, which is about:
1.40%.
So if the max torque and max power increased proportionally, which actually, they should, I would get an additional 2.5 hp......which is enough for a good grass trimmer/weedwacker.
 
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