QUOTE(Optiplex330 @ Jun 16 2012, 08:58 PM)
Are you sure? I would have thought the reverse is true
For street applications, blower sizing is as important a consideration as turbo sizing. A small blower works better at low speed and develops power more quickly than a large one. A large blower is great for top end power, but isn't as well suited to lower rpm operation because of its greater power burden on the engine.
One of the most important advantages of supercharging street engines is that it can transform a relatively stock motor into a real performer without a lot of expensive modifications. Supercharging can be a straight bolt-on installation, and it works well with stock heads, cams and pistons. What's more, it delivers better low speed throttle response and torque than a naturally aspirated engine with a big carburetor, big valves, high compression and "hot" cam.
Dyno tests have shown that a blower can be much more "streetable" than a naturally aspirated engine that's been built up to deliver an equivalent level of power. A blown engine is more streetable because it performs better at low rpms. A blower kit may cost several hundred dollars more to install than what it would take in equivalent engine modifications to obtain the same level of performance with a bigger carburetor or throttle body, hotter cam and modified heads. But the blown engine will deliver about 10% more power and torque in the lower speed ranges where it does the most good on the street. Besides that, a blown street motor looks great.
The ultimate in performance, of course, is achieved by building a motor specifically for the blower. Using a "blower" cam that optimizes the breathing characteristics of the blower can improve both low speed torque and high speed power. A long duration cam with a lot of overlap isn't good with a blower because the boost pressure goes in the intake valve and right out the exhaust port at low speed. What works best is a cam with little overlap, a lot of lift and duration but more lift and duration on the exhaust valves (since the blower does nothing to help evacuate the cylinders). With a turbocharged engine, more lift and duration is needed on the intake valve to prevent backpressure (created by the turbo) from backing up into the cylinder.
One caution to keep in mind with any kind of forced induction system is compression. Because of the extra air and fuel that's rammed into the cylinders, detonation can become a problem if compression gets out of hand. Most blown engines work best with a static compression ratio of less than 8:1 (7:1 or 7.5: 1 is best). The lower the static compression ratio, the higher the boost pressure you can safely run with the blower and the lower the rpm range at which the blower can develop peak torque.
The typical boost provided by either a turbocharger or a supercharger is 6 to 8 pounds per square inch (psi). Since normal atmospheric pressure is 14.7 psi at sea level, you can see that you are getting about 50-percent more air into the engine. Therefore, you would expect to get 50-percent more power. It's not perfectly efficient, though, so you might get a 30-percent to 40-percent improvement instead.
The key difference between a turbocharger and a supercharger is its power supply. Something has to supply the power to run the air compressor. In a supercharger, there is a belt that connects directly to the engine. It gets its power the same way that the water pump or alternator does. A turbocharger, on the other hand, gets its power from the exhaust stream. The exhaust runs through a turbine, which in turn spins the compressor
There are tradeoffs in both systems. In theory, a turbocharger is more efficient because it is using the "wasted" energy in the exhaust stream for its power source. On the other hand, a turbocharger causes some amount of back pressure in the exhaust system and tends to provide less boost until the engine is running at higher RPMs. Superchargers are easier to install but tend to be more expensive.
Edit: Source @ Schmidt, Third year engineering student in Oxford Brookes University.
This post has been edited by FenomX: Jun 16 2012, 09:09 PM