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Old 04-22-2004, 02:12 PM
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Keith I think the better quench make more power because of better combustion. The fuel mixture is nice and swirled and the fact that igniting at the right time and in the right place. I don't think in a race fuel application the difference would be as large as in a pump gas application.
Ben,
I can't really follow your example because you are not taking the cylinder head into account (or at least I don't see how you are). The combustion chamber is in the head, not in the cylinder (if you will). So the design (size and shape) of the cylinder head is just as important as the quench and piston top.

In your example I don't see how you can still have 10:1 in all three examples, I understand it was just in theory but, I think too many factors were left out. The top example would have the best quench though. The reason is (assuming a closed chamber head) the charge would be forced to the "open" part of the chamber because that is the only place for it to go. In your example the heads would all have to be flat or open chamber for your conclusion to be true.

Think of it as stepping on the edge of a water balloon. All the water will rush to the other edge, now if you step on the center the water goes in all directions. Same basic principle (which I am sure you understand the theory behind quench/squish). Since you know what it is, you have to understand what it does. The effect of the fuel rushing across the top of the piston and combustion chamber, cools (quenches). If you have no squish then you have no quench. You can have the same compression, but without the squish you have no quench. Yes, the engine will still run but, you have lost the quench effect. This is how the different "squish" (quench) heights make a difference.

With a large quench you are basically stepping on the middle of the balloon the mixture goes in all directions (out of control). This is why .035-.045 is the goal we shoot for. Much more than .045 and you no longer have squish. Running tighter than .035 would be even better but, you have to give room for rod stretch etc... Some guys like to build race engines so the piston just kisses the head when the piston rock at TDC, they say is make a little more power. Of course this is not something you would want to do in an engine you want to live for a while.

Once you get much over .045 it no longer makes a difference. So if you have a choice of .090 or .140 it really doesn't matter neither will have squish/quench.

I don't claim to know it all, I can only explain what I have learned/believe.

I hope that helps some?

Royce

Edit: blndweasel, we were typing at the same time. Excellent exapmle Very good way to look at it.
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