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Old 02-21-2004, 03:51 AM
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piston to valve clearance

needing to get a little info on my set up. what i have is a 396 .090" over. (402 .060") 4.185 bore i have gone with .110 dome pistons, this is the smallest dome i could get, to help with compression. (guessing to be around 10:1) closed chamber, 97cc heads. using comp mag 270h 224/224 @ .050, .510 lift in/ext. was worried about piston to valve clearance. when i clayed the pistons there was no valve impression left in the clay (no head gasket used) everything was done heads torqued and valve train installed. i thought it was going to be a tight clearance. obviously not! now i am worried about quench and pre-detonation. can anyone help me out here? i also would like to know an estimate of hp with this set up.

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Old 02-21-2004, 12:47 PM
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The only person that can tell what the quench is would be the builder of the engine. If it was even measured. Optimal is .040
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Old 02-21-2004, 06:14 PM
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quench

I am the builder and I am just wondering the importance of quench clearance. And the effect of not being within the.040. what kind of problems will this create?
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Old 02-21-2004, 10:34 PM
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Re: quench

Quote:
Originally posted by crazyman
I am the builder and I am just wondering the importance of quench clearance. And the effect of not being within the.040. what kind of problems will this create?
http://www.speedomotive.com/Building%20Tips.htm

You need to have the heads to physically measure your quench. What I do is take a straight edge and some spark plug gappinig feeler gauges and get the #1 piston to TDC. Rotate the engine slighty back and forth to verify actual TDC. Then use the feeler gauges to figure how far down the piston is. When you get this number add it to your head gasket thickness. That is your quench.

When you verify TDC with the straight edge, it is a good idea to look down at your timing pointer and make sure it is correct. Make sure TDC is really TDC.
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Old 02-22-2004, 03:51 AM
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quench

I follow what you are saying, but I am using .110" dome pistons. @ tdc the dome is actually in the cylinder head combustion chamber. I'm thinking I should of had more of an imprint in the clay when I checked the valve clearance. If I am confused with the meaning of quench and the effects of having too much, then please fill me in.
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Old 02-22-2004, 08:09 AM
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Quench or " Squish" as it is sometimes referred too, is measured at the flat part of the piston to the flat part of the head. This is important because when the piston is comming to top dead center in the combustion cycle, the chamber charge is already burning. The quench area determines whether the outer edge of the mixture gets moved away from the edge, towards the burning flame. The piston forces the edge charge across the top of the piston if the quench area is correct. This makes for more efficient combustion. If the mixture just lays there (like too much quench) it can pre-ignite(knock) or even wash down the rings. Depending on how bad the problem is. Too little quench can also make the engine octane sensitive, but the biggest problem is lack of clearance between the head and piston top (physical contact), caused by loosening wear tolerance and carbon buildup on the piston.
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Old 02-22-2004, 09:58 AM
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To add to what Bob said (he is right on by the way). You should shoot for .035-.045" of quench. If you are tighter than that you are looking at very possible piston to head clearance. If you are wider than that you are more likely to have detonation and it hurts performance slightly.

You do NOT need the heads to determine what the quench will be. What you do need is your deck height (how far the flat part of the piston is under the deck of the block), once you have that add the compressed thickness of the head gasket to it and that is your quench. The reason heads don't matter is, if you have closed chamber heads they all have a flat side to the combustion chamber. This flat side won't change, so you don't have to have the head to figure quench. Quench is the distance between the flat part of the piston and the flat part of the head, with the piston at TDC (top dead center).

You are using closed chamber heads right? If not, then all this talk about quench is basically moot for your application.

Royce
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Old 02-22-2004, 03:52 PM
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thanks to everyone! I obviously had the wrong meaning of quench. I was thinking it was the distance between the piston and valve. you all have cleared this up for me, thanks! now I can continue building my motor.
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