Maximum compression is dictated by how efficent the engines combustion process is and how stable of fuel you are willing to run to control the combustion process. When it comes to fuel and compression ratio, you try to run a fuel that is on the ragged edge of detonation, to stable of a fuel the combustion process is slowed. There is a point at which higher compression ratio starts to give minimum yields, per type of fuel being used. During the 1980's GM was working with gas combustion engines that had 100:1 compression ratio for emissions, the timing had to be so far retarded they didn't gain much of anything and had little results in emission. With compresson ratio, you have two problems, low compression, Oxides of Nitrogen is low and Carbon Monoxide is high. High compression, Oxides of Nitrogen is high and Carbon Monoxide is low.
Engine cubic displacement equals the volume displaced by the piston from the bottom of it's stroke to the top of its stroke multiplied by the number of cylinders. bore radius squared X 3.141 X stroke X number of cylinders = total cubic displacement Cylinder head volume, which greatly effects compression ratio, is usually measured in cubic centimeters, using a scientific graduated buret (and then converted into cubic inches when necessary). Another variable in compression ratio is the thicknes of the head gasket. To find the compression ratio divide the cubic volume of one cylinder by the volume of the head plus the volume of the head gasket. Cubic volume for one cylinder/cubic volume of head volume + cubic volume of gasket.
Howabout a simpler explanation? Cool technobabble is fine, but it doesn't do any good if nobody knows WTF you're talking about.
The basic rundown: You can run compression as high as you really want, until you run into problems with detonation. There is no hard-set rule about how high you can go on normal gasoline either, it's just a "try it and see how it works" thing.
Typically, very high compression engines suffer from detonation -- the fuel explodes before the engine is ready. Thus, your engine is still trying to "Squish" on that explosion and it makes pinging noises. Squishing an explosion is a very abusive thing to do to an engine which is why you damage engine parts when it's pinging.
But compression isn't the only factor that makes an engine ping... As you're well aware, higher octane gasoline is more resistant to detonation mostly because it burns slower. If you're getting pinging, higher octane gas will usually fix it. This is also why higher octane fuels don't do much for you when your car is NOT pinging.
However, there's even MORE cool stuff that makes your engine more resistant to detonation. For example: if the gasoline is very well atomized (a VERY fine and even mist) in the air, then it will burn cooler and in a more controlled fashion. This can be accomplished by better or more advanced fuel injection systems, better intake manifold design, and even by the way the pistons interact with the cylinder head.
Other things include dynamic compression ratio, where you figure how much ACTUAL compression you're getting based on how your cams are arranged. You can also talk about removing "hot spots" from the engine through better piston, combustion chamber and engine cooling design. A hot spot will make the fuel ignite before it's ready which leads to pinging -- so keeping hot spots out can also help.
Basically what it comes down to is this: The maximum compression you can run totally depends on what kind of fuel you want to use, what kind of cams you want to use, how much tradeoff you want for emissions versus power and the overal design of the internal combustion chamber space.
I don't know wtf the 2 of you are talking about but hey it's all good! <img src=/images/forums/snitz/approve.gif width=15 height=15 border=0> Red I don't care what that mean man has to say about you...your still my hero. Honestly, no sense in getting in a flame war over max compression but hey what ever floats yalls boat <img src=/images/forums/snitz/smile.gif width=15 height=15 border=0><img src=/images/forums/snitz/tongue.gif width=15 height=15 border=0><img src=/images/forums/snitz/smile.gif width=15 height=15 border=0>
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