This will be a supplementary discussion to the various other threads on improving combustion chambers or the benefits of a 4-valve head, etc. Using a topic title specifically for this subject will attract folks from other forums who can share their knowledge, even if it is from another engine design. I have been reading allot on the interweb lately about this subject. Seems to be a factor some consider to be a crucial foundation element while others aren't even aware what it is or does. From what I've gathered, done properly can mean running lots more compression than with it wrong. I'm wondering just how much proper squish, quench, quinch can do for a CRF230F? It all comes down to the burn. To be efficient it must be fast and complete. If it is then less timing advance is needed and more compression ratio can be used. Small engines have the advantage of small bore diameter which means less distance for the flame front to travel which means faster burn. Proper squish creates turbulence and eliminates small pockets where air/fuel mixture or fuel droplets can hide. It also reduces the Combustion Chamber volume. Since the 230F engine uses a 2-valve hemi or hemispherical combustion chamber, finding the ultimate design or shape will not send me to discuss tech with our more modern DOHC 4-valve pentroof brethren. No, we must go and seek the advice of the more ancient horsepower junkies like the American V8 tuners, Yamaha SR500 affectionados and even......gulp......them Harley fellers. If'n it ain't a pentroof design, some body has probably looked into improving the CC. I've searched to find a bore diameter vs. flame front speed relation or a distance from the spark plug the combustion chamber walls need to be at a maximum but haven't found anything discussed that way. I'm wondering if say a 67mm bore is small enough already that just eliminating the large OE squish gap, something around 0.080", will be enough to deter detonation with say 12:1 and pump gas? Will a 0.035 squish gap on our hemi head be enough or will we need to make the CC smaller, shorten the distance the flame front has to travel? Is the actual shape of the CC important? I have found that shallow CC are bad for turbulence and our good friend Mixxer suggested something with Hockey Puck dimensions is desirable, a 1:3 height:width ratio. What about the actual shape of the CC? The heart shape is popular on 2-valve wedge CC but a Hemi isn't a wedge. I've found more of the bath tub shape but all of the discussions have been on engines with LOTS MORE BORE DIAMETER and some with an intake valve diameter close to the bore size of the 230F. So they needed to make the CC smaller as well as optimize the squish band.