EFI Head Volume

Greg Hermann bearbvd at sni.net
Wed Apr 7 07:40:10 GMT 1999


>Hi Bruce:
>Lingenfelter's book on modifying small block chevy engine's on page 47-48
>says that "A performance piston-to-head clearance is usually between .040
>and .045 inch. This quench area is too small to support combustion, service
>instead a more useful function. As the piston approaches top dead center,
>this tight area tends to squirt or squish the air/fuel mixture in this area
>into the open combustion space. This violent action produces turbulence that
>acts like a very efficient blender. This blending action helps homogenize
>the air-fuel mixture and supports more efficient combustion.  Dyno testing
>has proven that improving the piston-to-head quench area from .060 inch to
>.045 inch will improve power even when the compression ratio remains the
>same.  It is even possible to optimize the quench and increase compression
>without suffering detonation problems! This is because improving the
>homogenization of the mixture in the chamber reduces the tendency for lean
>areas in the chamber to promote detonation. "
>
>I have my piston to head clearance set at .039 inch!
>11.0 to one with efi, aluminum heads and 92 octane unleaded!
>Mark

Precisely stated--the tight quench area helps AVOID detonation. More
clearance, or less area with tight clearance, is not so good.

Greg





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