Boost and PSI

[Mohamad]

When they talk about boost and size of pulley in superchargers this thing which I don’t understand. So the higher the psi the faster or slower? And in size if pulleys usually they higher the size of pulley the slower it is?

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[I Bleed Ford Blue]

Usually when the boost pressure or PSI goes up, so does hp. Pulley size depends on if it is a drive or driven pulley. The drive pulley is the one on the crank and when it gets bigger, the the boost goes up because it spins the belt faster for a given rpm. The upper or driven pulley gets faster and creates more boost when it gets smaller.

 

[ForYourOwnGood]

When they talk about boost and size of pulley in superchargers this thing which I don’t understand. So the higher the psi the faster or slower? And in size if pulleys usually they higher the size of pulley the slower it is?

It depends. Boost PSI is a measure of restriction, you see it increase as you spin the blower faster (smaller pulley) because you're forcing more air into the motor. Thats why you might lose some boost when you go to long tube headers or ported heads, less restriction. Generally if you're going down a pulley size you'll make more power if its set up right, but you'll also make more heat and require more octane to keep the same spark advance so it is possible that if you're at the edge of what your chosen fuel can do you might not make any more.

 

[ahl395]

Smaller pulley = more boost = more power = faster

PSI is just how you measure boost.

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