This topic was brought up before, but locked for some dumb reason. I found a 12V fan that blows 250cfm of air. Some claim it is a very cheap alternative to a turbo, but I know better than to believe this sort of nonsense. In fact, it doesn't create more than 1psi of boost. In my case however, I using it as a ram air in-line with my intake. The problem is that I only want it on at WOT. Can anyone help me?
With an 1800 cc engine, the full displacement passes through the intake every 2 revolutions, assuming no restrictions.
At 3K to 5K RPM, where you want to boost the torque, the engine displaces 2,700,000 to 4,500,000 cc each minute, or 95 to 159 cfm. 8000 RPM equates to about 255 cfm.
We all know that there are restrictions in the intake system, so there is actually less flow than listed above.
If a fan could move 250 cfm regardless of the intake pressure buildup, that would work fine. However, most fans are rated for use where there is little restriction and the inlet and outlet pressure is assumed to be equal. Use a 250 cfm PUMP and you will have something.
That is the extent of my seat-of-the-pants analysis.