In the above post I noted the old pistons were .030 below the deck. Oddly enough this WAS the correct spec "back in the day". But back then they either didn't care about "squish" and "quench" or didn't need to because 100 octane gas was readily available. Drop the piston and your ASSURED of plenty of valve clearance with even RADICAL valve lift.
...move ahead 40 years. 100 octane gas is hard to find! Combustion research has progessed big time! We NOW know that "squish" is a good thing. Note the flat area of the piston and how that part "matches" up with the flat part of the heads combustion chamber. When those two "flat" surfaces meet the compressed gases trapped between them are "squished". If the piston is to far below the deck (.030 plus head gasket thickness) there isn't nearly as much "squish" going on. So move the piston to "zero" and squish the heck out of it!
Those "squished" gases get accellerated out into the combustion chamber at very high velocity. This creates a kind of "swirl" effect or at least get the fuel/air mixture really excited! Thus, promoting better over all combustion. "Quench" is the cooling effect that occurs and this helps to control the "burn" across the face of the piston.
I'm NOT an "expert" at this "science" and may not have it exactly right, but thats basically whats happening.
Your gonna love the next installement. The pistons are going in WITHOUT being "soaked", "dipped" or "coated" with engine
oil!! In fact I'm not even wiping down the cylinder bores with engine
oil before putting them in the bore! SAY WHAT? Am I CRAZY???
Stay tuned........
