Turbo vs Supercharger

I was running 15.5 psi on a Dodge 5.9. 6.5 psi on my 2.7, but it could have easilly handled more. As long as the fueling is right, and the internals are strong enough. 6.5 psi from an SC is the same as 6.5 from a turbo.

 

Its a blockage in the exhaust system. Its not "Free h.p.". A turbo DOES have a parasitic drag on the engine. Install a Turbo on a engine but instead of connecting the intake, run the stock intake. Do the same with a blower. The two will be very similar in the amount of h.p. lost, via parasitic drag. Also, Turbos creat boost with a centrifugal type blower. They dont move alot of air by volume, thus they need a higher psi to fill the combustion chamber with a desiered charge. Most SC's are a Positive displacement type blower. I.e., an Eaton M62 moves 62 cubic inches of air per rotation. They move MUCH more air thus they can run less boost. Why do you think Top fuel cars use a SC instead of Turbos? I have found that running a much larger blower than whats recomended, but running less boost, yeilds the same power, and a cooler intake charge air temp. Makeing tuneing much more easy. With a Turbo, not only is the air heated via higher psi, but also, as the turbine is driven by the exhaust, the intake turbine absorbs this heat, and transferes it to the intake air.

 

Most superchargers today have a bypass valve that allows normal engine mpg under non boost conditions. When I boosted my 2000 Tacoma, I saw no change in mpg. and in some cases it was better.

 

Most all superchargers for street vehicles have a bypass valve. Race applications dont, as there is not really a need for them under WOT conditions.
The super charger I used was an Alpine SC.
http://www.alpine-developments.us/wwwroot/toy00super.htm

On the rear of the unit, you see the "can" that uses vaccume to opperate the pypass valve. The TRD superchargers are the same. The Supercharger's I have used on other vehicles were Kenne Bell chargers, and had a similar set up. On a street aplication, a pypass valve MUST be used otherwise, a rough idle condition occuers, and it leads to drivability problems when not under boost conditions, also known as compresser surge.
http://www.superchargersonline.com/content.asp?ID=14
http://www.superchargersonline.com/content.asp?ID=85
The Bypass Valve
Compressor surge is a problem that affects most superchargers and develops when the supercharger is creating boost, but the throttle shaft is closed. Although not a problem on some low-boost (5psi or less) applications This condition can occur under deceleration or while shifting between gears, and can cause the car to sputter and chirp. Under surge, the compressor forces air into the closed throttle body until the pressure inside the throttle body is higher than the amount of pressure being created by the supercharger, and the air tries to pop backward through the supercharger. At that point, pressure is released inside the throttle body and the compressor forces air back through the supercharger and into the throttle body, which again has nowhere to go, and the process repeats. While surge normally is not highly damaging to the engine it is certainly annoying and can cause damage with time. To eliminate these problems under surge conditions, a bypass valve (sometimes called an anti-surge valve) is used to release the excess pressure. The bypass valve is actuated using intake manifold vaccuum, which opens the vent valve and releases pressure in the air-intake. Air is either released into the atmoshpere (blowoff valve) or recirculated back through the supercharger compressor (bypass valve).