Or,,, would that be "squish" your looking for? I visited this issue during my recent engine build blog (427 side oiler). More here:
427 side oiler engine build "Blog"
Basically squish is where the flat part of the piston meets up with the flat part of the combustion chamber. These two "flat surfaces" IF they come in very close contact to each other "squish" the compressed gases to such a high degree those compressed gases are "shot" out of that space across the face of the combustion chamber at GREAT velocity, thus "exciting" the rest of the combustion gases and promoting a better over all "burn".
In order to get "squish" you MUST HAVE close to or be at zero deck height on your piston. You must also have the two "flat places" that match, piston and combustion chamber area. Valve clearance is an entirely separate issue, by the way.
Quench? Well I barely figured out squish. But I DO know "quench" is in refference to dealing with hot spots and controlling the "burn" in the combustion chamber. You want a nice steady controlled burn across the face of the piston and the gases continuing to expand and drive that piston down with ever greater force until the combustion gases are "nearly" spent. You DON'T want errectic hot spots starting the "burn" here and there and getting out of control, heck THATS what we call "ping" or "detonation". BUT, how do you "design" for quench? Or do you focus on squish and quench happens?
...this stuff is more like "Zen" than science I tell you.
OH, this thought comes to mind! Not only piston "deck height" is critical to achieving good squish\quench but also piston to cylinder wall clearance must be kept "tight". My OLD pistons had over .006 clearance cylinder wall and .030 deck height. Result? NO SQUISH AT ALL! This was "old school" thinking. The more clearance a piston has the more it "rocks" within the cylinder. That rocking action WILL impact the "squish" zone clearance factor. .060 "squsih area" is generally considered "safe", less makes more power but become "dangerous" for longevity issues. Keep the piston tight to control the rock and thus "nail down" the squish. My current custom pistons are .0035 and zero deck height (looking for hidden horse power was my goal). I'm NOT an "engine expert", just a guy who built his own motor and did a LOT of reading and listening.
Andy "The Butcher" Dunn recently made a rather profound comment concering the engine he built for the "Engine Masters" contest. He said something about the combustion chamber burn rate is more important concerning the PISTON area than it is the combustion chamber area! I'll still thinking about what THAT means. I suspect the size, shape, design of the piston dome or lack thereof is of more importance than the shape/size of the heads combustion chamber area.
Quench?
Linear Mode
