combustion chamber

[HotRoddin]

Originally posted by lx5091
Better yet, what is the maximum size valves neccessary to fill a 58cc chamber on a naturally aspirated motor? Could an intake keep up (any brand)? Or is that even the point?

You aren't just filling the combustion chamber lx you're filling that entire space from the top of the piston when its all the way down in the bore (bottom dead center) all the way up to and including the cavity in the head (combustion chamber), and at 6,000 RPM you're filling that space somewhere in the neighborhood of 50 times a second per cylinder. So that valve has to be big enough to flow quite a bit of air and fuel ! You want the intake valve and intake port to be big enough to not severely restrict flow, but at the same time it can't be so big that you lose the speed of that flow (everything in a racing motor is a trade off ). What you really want is a head that has valves and ports big enough to maintain good flow numbers but still maintains good air fuel velocity through the intake ports and on into the combustion chamber. The exhaust valves and ports just need to flow well throughout the cams lift range ... velocity isn't very important on the exhaust side, just good flow. You also want a combustion chamber shape that creates the proper turbulence to promote a fast clean complete burn of the air fuel mixture when it ignites.
The size of the chamber primarily effects the compression ratio. The smaller the chamber, the higher the compression ratio (that is if everything else remains the same).
Sorry that was so long winded but all those things are so inner related its difficult to discuss it without writing a book!