Originally Posted by RCZ

Hmm, You change the pulley to change the multiplier effect of the gear size differences and therefore the speed at which the compressor wheel is moving. Higher speed will yield more boost as long as the turbine wheel is within its efficiency range.

Changing the housing would be like getting a different trim and thats the same as getting a whole different supercharger.

You made your post sound like you were talking about spooling when you said "full spool". I don't know if you know this, but spooling refers to the amount of time it takes air exiting your engine to spin up (spool up) the exhaust turbine on a turbo. You are talking about a supercharger spooling? It doesnt spool, it spins up and down with engine speed. That engine speed + gear ratios between the crank pulley and the sc's pulley is what creates a certain speed in the compressor wheel. You are right about one thing though, the housing does affect the way power is delivered because different sized compressor wheels have different effects, speed being the same, with relation to their size. I didnt say it didnt, I said it doesnt have a difference on the "spool" of it because it is belt driven.

The size of the compressor wheel has no bearing on its speed. OK yea the tips of the blades are spinning faster because they are traveling more distance in the same rotation, but thats not what we are talking about here. Whether the compressor wheel is 2 inches in diameter or 4, its still spinning at a certain RPM that is produced by the gearing size differences in the pulleys. A bigger wheel should in theory move more air at the same RPM as a smaller wheel, granted I think each size probably has a different peak efficiency speed, I don't know, I didnt study turbines or fluid dynamics in college. Remember we arent changing the compressor wheel size when you upgrade, you usually change the pulley size to increase the multiplier effect and speed up the compressor per a given RPM and therefore making more boost. That is why bigger housings make more power, because they can move more air per rpm than the smaller housing. In other words they make more boost per rpm. You would only move up in housing when you have maxed out the efficiency zone/speed of the smaller housing.

You even brought up turbos and you are confusing the size thing with the SC. The turbo's are the ones that will produce boost quicker when they are smaller, but thats not because of the smaller compressor housing, its because of the smaller size of the hotside that needs to be filled up and spun up with exhaust air. The smaller that is the quicker the shaft spins up the quicker the compressor builds boost.