high compression = less cc ?

[zeppelin]

okay this idea just hit me a couple weeks ago and nobdy understands me when i ask them about it so i figred i would ask yall. a higher compresion pistion has more meterial on the top of it to raise the compression, right, so it is almost like destroking the motor( the top of the piston doesnt go down as far as it did before it had the extra meterial) ahh this is hard to explain just look at the pictures and tell me if im completely nuts or not

[zeppelin]

see uhh this is hard to put in words but yall get the idea

[2muchquad]

the bore and stroke of the engine doesnt change.true your gonna have a smaller squish area at tdc but your displacement will be the same because you still have your same bore x stroke to get your displacement.doesnt matter if you had a flat top piston or a domed piston,bore x stroke will not change:)

[zeppelin]

i dont see how you coulnt lose the stroke though, damnit this is hard to explain lol, okay if the high comp it 2 mm taller at tdc to raise the comp. then it also has to be 2mm taller at bdc, it seems to me that all high comp pistn make you loose stroke

[Fred55]

If the piston is taller on the up part of the stroke it will also be taller on the bottom, there for there is no change in how much the piston moves from up to down.

[2004exrider]

I know exactly what your trying to say, since the piston is a little taller its not going to be able to suck in as much air as it did with a lower compression piston. But its not gonna change the cc's. The formula for that is:
CC = .7854 x bore (mm) x bore (mm) x stroke (mm) x the number of cylinders. Then take that answer and divide it by 1,000, you will now have your amount of cubic centimeters.

Jimmy

[humblesquirel21]

the way i understand all this is ur adding x amount of mm to the top of the piston to achieve higher compresion wich means it wont go down as low but at tdc it would be that much higher so it evens out if that makes sence

[zeppelin]

okay let me put it kike this if you measure the distance from the top of the cylinder down to the top of the piston at bdc, that it doesnt matter iffthe high comp is higher, just as long as the total distance traveld be the piston is the same

[lt250rm]

stroke doen't change all that changes is your combustion chamber size which is smaller now and will compress the air fuel mixture to a smaller size. Which is why you have to run higher octane because higher octane fuel will compress and won't pre ignite which will if its a big enough pre ignite it will force the piston back down in the direction it just came up and bend the rod, blow a hole in the piston and break the crank and you have a chunk of scrap aluminum now.

[2004exrider]

Originally posted by zeppelin
okay let me put it kike this if you measure the distance from the top of the cylinder down to the top of the piston at bdc, that it doesnt matter iffthe high comp is higher, just as long as the total distance traveld be the piston is the same

Yes.

[Chino886]

Where is Wilkin250R when you need him?

[lt250rm]

i get what you are trying to say you'd think it would change but it doesn't. the raisd part doesn't actually look like you made in the picture. its actually the shape of the combustion chamber its not flat like that. If it was flat the valves would smack the top of the piston on the intake and exhaust stroke. Its hard to explane it but i know exactly what your talking about.

[nakomis0]

Stroke is from what the crank throws. Crank and rod.

Piston height has nuttin to do with it. Reguardless of how tall the piston is the stroke will still be the same.

[bwamos]

I think he's just mixing up cylinder volume with static displacement.

Static Displacement is the amount of volume the cylinder displaces throughout it's stroke. It stays the same no matter what compression you run. 7:1 or 16:1 it will still be the same.

Overall volume of the combustion chamber will decrease by a small amount at BDC, but that is virtually irrelevant.

Dynamic displacement/compression is what really matters. Good port work & cam combo will get more air/fuel mix into the system during it's intake stroke and actually give you a higher or lower actual displacement than the static value depending on your porting, cam, etc..

[wilkin250r]

Originally posted by Chino886
Where is Wilkin250R when you need him?

I don't get on much on the weekends.

Zepplin, your last post is closest to the answer you're looking for. But just because the piston crown is closer to the head at BDC doesn't mean it's been destroked. It also starts closer to the head.

Even though the top of the piston may be at a different place with a high-comp piston, it still travels the exact same distance. Your stroke is determined by how far the connecting rod is located from the center of the crank.

Regardless of where the piston crown actually starts and stops, it still travels the exact same distance.