this might be intresting
In fact the ultimate horsepower potential of any engine is really a function of the flow capacity of the induction system. By just increasing engine size, say with a longer stroke crank, we will increase torque at low rpm but not necessarily increase peak horsepower by much at all. The flow capacity of the induction system imposes the ultimate limit on the amount of air that the engine can process per minute and whether we have a small engine running at high speed or a big engine running at low speed, it is total airflow per minute that matters. The only real difference between a 3 litre car engine producing 200 bhp and a 3 litre Formula 1 engine producing 800 bhp is the flow capacity of the cylinder head.
well, When it comes to squeezing more horsepower out of a given number of cubic inches, nothing beats a blower (except maybe a turbocharger, which is the rival form of forced induction). The amount of power any engine produces depends on how much air/fuel mixture is pumped through it in a given instant of time. To increase the engine's power output, therefore, you either have to increase the engine's displacement (more cubic inches), increase rpm or increase breathing efficiency (called "volumetric" efficiency).
Engine speed naturally goes up when the throttle is punched opened, so for an engine of a given displacement the fastest route to more power is to increase its volumetric efficiency. A bigger carburetor, a better flowing intake manifold, a cam with more lift, duration and overlap, opening up the head ports, bigger valves and a free flowing exhaust are all traditional means by which an engine can ingest and pass more air and fuel. But even the best built naturally aspirated engine will never achieve 100 percent volumetric efficiency because atmospheric pressure can only do so much to overcome the restrictions and turbulence in the intake system. And as rpms go up, volumetric efficiency drops off.
The only way to overcome this limitation is to add a forced induction system. By mechanically increasing the volume of air that enters the engine, forced induction in effect increases atmospheric pressure giving the air more "push" as it enters the cylinders. Volumetric efficiency goes up and the engine makes substantially more power. Now the engine can breathe at 100 percent volumetric efficiency or higher depending on how much "boost" is built into the system. Crank up the boost pressure and even a little engine will come to life. That's the secret for squeezing hundreds of horsepower out of relatively small displacement four, six and even eight cylinder engines.
