??? I HAVE BEEN WONDERING AND CAN'T SEEM TO GET A STRAIGHT ANSWER ON WHAT CASE VOLUME AFFECTS.SAY I HAVE A THEORETICAL ENGINE AND I CUT THE CASE VOLUME IN HALF-NOT CHANGING ANYTHING ELSE- HOW WOULD THIS AFFECT THE ENGINE? HOW ABOUT IF I DOUBLED IT, WHAT WOULD IT DO? IS THERE A "IDEAL NUMBER" FOR THIS?

I've been told that a smaller volume promotes better cylinder filling during the transfer cycle. I would assume that larger volume reduces filling. As far as ideal volume, I would think the smaller the better. Some manufacturers incorporate "stuffers" into the crankshaft assembly just to reduce case volume.

Your question is a complicated one and there is not a "one answer" for all answer to it.

In very simplistic terms... Higher primary compression (smaller crankcase volume) allows for more velocity in the transfer tunnels after blow down phase is completed. This can be a good or bad thing. Excessive velocity Can cause the newly scavenged f/a mix to blow right out the exhaust port. It can also overscavenge the engine.

Too little or primary compression (larger volumes) will slow transfer velocity and could cause the cylinder to be underscavenged.

There is much more to this but that is a few characteristics.

Hope it helped.

Kelsey

Kelsey, is there any way to raise primary compression

decreasing case volume will increase primary compression, think of that crank as a
pump that pushes the air/fuel mixture into the cylinder.

wont a longer intake incease primary compression?