Quote:
Originally Posted by Wonderbar
I'm all for starting an actually thread on the differences between exhaust driven turbos and belt driven superchargers.
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Superchargers don't make up for altitude. Only turbo's do that because the boost that is entering the motor is tied to a turbo that is controlled by a wastegate that will keep a certain set pressure. This wastegate looks for a certain manifold pressure and tries to maintain it irregardless of what atmospheric pressure you are at.
High altitude has less pressure to begin with so a turbo will spin harder to make, say 10 psi at 6000ft. How does it work harder? The wastegate keeps shut untill manifold pressure reaches the set point. This set point is harder to reach at altitude. This set up would still make 10 psi at sea level, but the turbo wouldn't be working as hard.
A supercharger has no such mechanism to "keep the same pressure" in the manifold. A supercharged system that makes 10 psi at sea level would make, for example, 7 psi at high altitude. There is no wastegate to allow the supercharger to work harder to maintain 10 psi.
You can think about it like this:
A turbo can be made to work harder in order to maintain a set manifold pressure. A belt driven supercharger cannot. A belt driven supercharger works "X amount" and cannot work more than X amount unless you rev higher or change the pulley so that it works X + Y amount.
Ex.
X amount of work = 10 psi at sea level
X amount of work = 7 psi at 6000 ft