Quote:

Patrick and rtman, you guys are mentioning quench numbers. How is quench determined? A combination of heads and pistons? What quench numbers are best with a set of magnum heads?



quench is the distance from the flat part of the combustion chamber to the top of the piston. for a close chambered head (302, magnum, edelbrock, indy), it's just the amount the piston is below deck plus the head gasket thickness.

for an open chambered head, it's the amount the piston is below deck plus the head gasket thickness plus the depth of the chamber (which as cast or depending on how much milling was done can vary from near zero to .1"+)

Quench helps improve detonation resistance by adding turbulence in the combustion chamber, providing for better fuel distribution. This allows you to run more compression with a lower grade of gas. .035" is about the minimum you want to avoid contact due to thermal expansion or the piston rocking in the bore, much beyond .060" and it has no real effect. some guys here with 360's and a comp XE268 sized cam need to run 93 octane with open chambered heads and no quench and compression in the 9.5-10.0 range, while others with similar cams with magnum heads and tight quench are in the 10.5-10.8 range for compression and can run on 89 octane.

I recommend if you don't have an engine yet, get one with a factory roller cam and start with that. that's an 85-up 318 or 89 and up 360. the roller lifters can be reused, the cam reground, it'll make more power than a similar duration flat tappet cam, and you don't have to worry about the cam going flat due to the lack of zinc in modern oils

Last edited by patrick; 08/28/09 09:08 AM.
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