I'll give this a crack.....,

The 300cfm is with a lower compression piston.

A engine is a air pump, that's it. The more air you can ram throught the thing, the more power you will make. Forced induction (i.e. turbo, supercharger) is a mechanical device which will ram more air into the cylinder then the piston is at its lowest point inside the engine. Remember the more air ( and fuel, the ratio must be balanced at 14.7:1) the more power.

Now, why would you want to mess with the pistons? If you lower the compression ratio with modified pistons..... lowering the compression ratio, you can force more air + fuel into the same engine = more power. The area inside the cylinder when the piston is at it's lowest point (BDC) can now have more air + fuel crammed into it = more power.

One more important thing to mention, when you compress air you get heat, a turbo will create a ton of heat into the incoming air. When you do this without cooling the air (i.e. intercooler), the engine is more likely to detonate or ping, severe detonation can put a hole threw a pistion, not good. Also, the more heat in the air, the less power you will make.

Heat is the enemy in this little picture. If we simpley cranked the boost up on a high compression engine to begin with, you would have big headaches with the heat ( detonation). With the resonable boost levels of 5-7 psi, a nice balance is being struck in regards to what amount of heat ( again detonation) could damage internal parts and the amount of heat is being put into the cylinder (more heat = robbing power).

I hope I didn't confuse anyone hear??