Ok, another basic question (engine related)

mcphelps · 08-11-2009, 09:57 AM

The higher compression piston lowers the volume of the combustion chamber.

It's a matter of taking the 0.616 liters (3.7/6)of air/fuel mixure you sucked in on the intake stroke and compressing it into a space that now has less volume. Compressing 0.616 liters into the volume of a golf ball will have higher pressure than compressing into into the volume of a baseball.

KusoSama · 07-11-2011, 05:53 PM

Quote:

Originally Posted by mcphelps

The higher compression piston lowers the volume of the combustion chamber.

It's a matter of taking the 0.616 liters (3.7/6)of air/fuel mixure you sucked in on the intake stroke and compressing it into a space that now has less volume. Compressing 0.616 liters into the volume of a golf ball will have higher pressure than compressing into into the volume of a baseball.

The way this thread was going I was worried nobody was going to point that out.

It's like saying that a piece of dynamite loosely packed versus tightly packed has a different stick size...

axeman71 · 07-11-2011, 06:37 PM

Ahhh, I get it now. I was writing a post agreeing with kannibul when the answer dawned on me. See if this example helps (or tell me if I'm all screwed up).

Lets make a theoretical cylinder that has 0.6L capacity on its down stroke and 0.1L capacity on its up stroke. I'll call that a 6:1 ratio (I don't know if that is how they measure a real cylinder but it will work for this example). So when the cylinder travels down it sucks in 0.5L of air since 0.1L was already there at the top of the stroke. Now we change out the cylinder head with a taller cylinder and leave everything else the same. You now have 0.05L on the up stroke and 0.55L on the down stroke. This gives you a new compression ratio of 11:1.

Your stroke is still the same. It sucks in 0.5L of air just like the original cylinder but it squeezes it into a smaller volume.

Dizon248 · 07-12-2011, 04:56 PM

Quote:

Originally Posted by axeman71

Ahhh, I get it now. I was writing a post agreeing with kannibul when the answer dawned on me. See if this example helps (or tell me if I'm all screwed up).

Lets make a theoretical cylinder that has 0.6L capacity on its down stroke and 0.1L capacity on its up stroke. I'll call that a 6:1 ratio (I don't know if that is how they measure a real cylinder but it will work for this example). So when the cylinder travels down it sucks in 0.5L of air since 0.1L was already there at the top of the stroke. Now we change out the cylinder head with a taller cylinder and leave everything else the same. You now have 0.05L on the up stroke and 0.55L on the down stroke. This gives you a new compression ratio of 11:1.

Your stroke is still the same. It sucks in 0.5L of air just like the original cylinder but it squeezes it into a smaller volume.

Looks good to me! We have our winner!!!!

08-11-2009, 09:57 AM	#1 (permalink)
mcphelps Base Member Join Date: Mar 2009 Location: Tucson, AZ Age: 68 Posts: 113 Drives: 09 Sprt/Tr/Nav PG M6 Rep Power: 18	The higher compression piston lowers the volume of the combustion chamber. It's a matter of taking the 0.616 liters (3.7/6)of air/fuel mixure you sucked in on the intake stroke and compressing it into a space that now has less volume. Compressing 0.616 liters into the volume of a golf ball will have higher pressure than compressing into into the volume of a baseball. Last edited by mcphelps; 08-11-2009 at 10:11 AM.

07-11-2011, 06:37 PM	#3 (permalink)
axeman71 Base Member Join Date: May 2010 Location: Augusta, GA Posts: 129 Drives: '10 Conv A7 Blk Chry Rep Power: 17	Ahhh, I get it now. I was writing a post agreeing with kannibul when the answer dawned on me. See if this example helps (or tell me if I'm all screwed up). Lets make a theoretical cylinder that has 0.6L capacity on its down stroke and 0.1L capacity on its up stroke. I'll call that a 6:1 ratio (I don't know if that is how they measure a real cylinder but it will work for this example). So when the cylinder travels down it sucks in 0.5L of air since 0.1L was already there at the top of the stroke. Now we change out the cylinder head with a taller cylinder and leave everything else the same. You now have 0.05L on the up stroke and 0.55L on the down stroke. This gives you a new compression ratio of 11:1. Your stroke is still the same. It sucks in 0.5L of air just like the original cylinder but it squeezes it into a smaller volume. __________________ 2010 Roadster, 7AT, Black Cherry, Touring, Navigation, Lighted Kick Plates, Floor and Trunk Mats.

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