ICQ>

You have to have a minimum pressure before there are any improvements in performance. This pressure is somewhere around 1.5 psi but does vary depending on engine and its camshaft, exhaust, etc.

A fan would not reach this pressure.

The reason you must reach this pressure is that there are already pressure pulsations that occur inside intake from the valves closing and reflecting the pressure back into plenum of intake. This is why there is a "tuned" intake on Volvo and most all other engines w/o turbos, the intake makes use of the pressure pulses to force air into the next opening valves for next cylinder in firing sequence. There is some validity to decreasing any restrctions in intake system but this is usually only noticeable in very minor improvements in top speed, not in normal acceleration where you would notice.

If a fan would help performance volvo wouldn't put turbos on the motors.

Just remember the first rule of physics : TANSTAAFL. (there ain't no such thing as a free lunch)