Quench?

Fishbreath, in hemispherical engine's heads, the quench area is actually 100% over the piston. It is the same with pent roof combustion chambers and applies to 348 and 409 Chevies and the old 430 Lincolns. The wedge chamber became popular in production because it was easier to cast and machine. All the old Chrysler hemi chambers were 100% machined! Holding the exhaust valve open longer helped to scavenge and "sweep" the chamber of foul residual combustion products. Buick did the same thing effectively with their "nailheads". The quench area, say in a 340, is like "taint"...it's that flat spot on the piston not included in the main squeeze of the combustion chamber. As the piston approaches TDC, whatever fuel/air volume is in that tight squeeze (quench) area between the piston deck and the head is eliminated from most of the flame travel...thereby "quenched". Material in that small clearance volume is forced out into the flame front at high speed and promotes combustion. This is the advantage many see in the wedgie over the hemi. I hope I didn't muddy the waters. The tighter the quench area, the higher the static compression ratio and the higher the dynamic compression ratio as well. Just how much timing a tight quench engine likes is dependent upon a lot of variables. I still say nothing beats a hemi because the quench area IS over the entire dome with the plug firing near the center and nothing interferes with flame propogation. Look at the hemi valve angles and sizes! Nothing feeds on fuel and poops gases better than the hemi design! Todays better alloys have helped to reduce the weight of a high compression hemi piston. Top fuel pistons are really heavy slugs with really thick domes and flat tops and they are tuned "down in the hole". I've seen the tops of these pistons CONCAVED coming out of Don's last Top Fuel car!! The smart hemi racers do all they can to get as light a piston they can get with as big a dome as they can get with the least amount of compression height (center of pin to lowest part of deck). The power stroke on a normally aspirated hemi never bothers a piston even with dykes rings mounted way up but if that piston has a big compression height, the connecting rod feels it really big time at TDC on the exhaust stroke! It's like you tied a rope to a cinder block and swung it around like you were the crankshaft and then stopped it at one point and tried to "instantly" change it's direction. It will try to pull your arm out of its socket! That's what a rod feels with a heavy piston on the end at TDC on the exhaust stroke.
Pat