Originally Posted by helldorado

A lot of it comes from that they're using a roots blower. With a CSC, lysolm or turbo, the air that comes from the turbine outlet is already compressed. With a roots blower, it just comes out faster, but still at atmosphere pressure. They don't compress the air within the unit, like the others do. The compression takes place between the blower and intake valves, in your intake manifold.

On a 4 stroke cycle, when the piston is dropping down the cylinder and the intake valve opens, a vacuum is created in the cylinder. Because of the overlap portion of the cam duration, the exhaust valve is still open. An appropriate level of back pressure allows the incoming air/fuel mixture to completely fill the cylinder. Too much back pressure, keeps exhaust gases in the cylinder, not enough draws the air/fuel mixture out through the exhaust valve.

So on a boosted application, since the intake manifold is no longer at atmospheric pressure, the pressure there is pretty much always higher than the pressure in the exhaust, so during the overlap phase, some of the air/fuel mixture is pushed out the exhaust valve. With a turbo or csc, the air that is added is already pressurized so its easier for the entire intake manifold to retain that air pressure level as air is rushing out the exhaust manifold. With the roots blower, it has to repressurize the entire intake manifold by pushing more ambient air into the chamber.

Since a roots blower is positive displacement, it pushes a fixed amount of air per revolution. So when the intake manifold pressure drops, there is only so much the unit can do to raise it back up and add extra air to the mix. This is extremely tough for the unit at higher rpms, why the Stillen doesn't generate huge peak whp. But at lower rpms, its much easier since the valves stay open longer. Why it generates such great low end torque.

Its not as much that you need a lot of backpressure for the unit to operate. Its that you need the right amount to keep the pressurized air/fuel mix from going straight out the exhaust valve and keeping it in the cylinder for maximum power. And the right amount is pretty much at stock backpressure levels.

Originally Posted by joe603

VERY well written!! Thanks..I've wondered about this as well.

Originally Posted by nickvvv

Hey guys. Just got myself an 04 coupe 5at. Been reading up alot about the car, don't know to much about cars. The only way to learn is to read and do it yourself. I've figured doing a bunch of little mods seems pretty pointless because I wont get to much hp out of them, especially for the amount of money it costs. So i was gonna go with the stillen sc kit that i seen on there website for $3800 roughly. My buddy from work is pretty heavy into cars and has owned a mustang for a long time and was telling me that this kit doesnt come with a intercooler, which is true, but u can get this other part which hooks up and sprays wiper fluid/water into I guess the intake to cool the engine down and u gain about 80 hp to replace the intercooler. Just wondering if this is true, and if its worth the money to buy the stillen supercharger.

Originally Posted by nickvvv

Hey guys. Just got myself an 04 coupe 5at. Been reading up alot about the car, don't know to much about cars. The only way to learn is to read and do it yourself. I've figured doing a bunch of little mods seems pretty pointless because I wont get to much hp out of them, especially for the amount of money it costs. So i was gonna go with the stillen sc kit that i seen on there website for $3800 roughly. My buddy from work is pretty heavy into cars and has owned a mustang for a long time and was telling me that this kit doesnt come with a intercooler, which is true, but u can get this other part which hooks up and sprays wiper fluid/water into I guess the intake to cool the engine down and u gain about 80 hp to replace the intercooler. Just wondering if this is true, and if its worth the money to buy the stillen supercharger.