[lust4speed]

The stock engines I've torn down have all been .005" to .008" in the hole, and I haven't come across deeper ones. Maybe just luck of the draw.

Anyone want to tell the Mopar hemi guys that quench is necessary for horsepower?

The couple tech papers that I've read indicate that there is a no-man's zone between .050" and .080" that is very prone to detonation, and staying below or above the zone is necessary. This would explain why hemispherical heads are fine. The math also says that with a standard .039" thick head gasket then the piston should be no more than .011" down in the hole before additional risk of detonation occurs. Something gets nasty with flame travel in that zone that doesn't happen with less or more clearance.

The race shop I used told me that they have switched to fully dished pistons for short track engines because their testing found additional power over the currently favored D-shaped top. My guess would be that lazy low RPM engines could use the "puff" of mixture being swirled while high RPM max effort engines there is enough mixture turbulence that any additional swirl doesn't help.

Even with fully dished pistons there is about a 3/8" flat around the circumference of the piston, and when you come down to it there really isn't much more being offered by the D-shaped dished pistons.

[69gtocv]

[QUOTE=lust4speed;6595621]The stock engines I've torn down have all been .005" to .008" in the hole, and I haven't come across deeper ones. Maybe just luck of the draw.

I just tore down my 72 400 that had never been apart. I got .007 in the hole for the two cylinders I checked. I was surprised they were that close to the top

[grivera]

Originally Posted by lust4speed

The stock engines I've torn down have all been .005" to .008" in the hole, and I haven't come across deeper ones. Maybe just luck of the draw.


The couple tech papers that I've read indicate that there is a no-man's zone between .050" and .080" that is very prone to detonation, and staying below or above the zone is necessary. This would explain why hemispherical heads are fine. The math also says that with a standard .039" thick head gasket then the piston should be no more than .011" down in the hole before additional risk of detonation occurs. Something gets nasty with flame travel in that zone that doesn't happen with less or more clearance.

With factory head gaskets at .045, seems they'd be detonation prone as built.