So I'm trying to decide what size pulley to go with when I get for my supercharger. I currently have a 6" crank pulley with a 3" s/c pulley which makes 4.5lbs of boost and has an impeller speed of 35380 at redline. I would like to make 6-7 lbs of boost but don't know what size pulley to get. If I went with a 2.75" pulley that would turn the impeller at 38596 rpm's which is about an 8% increase. Does that mean I will see an 8% increase in boost? I'm just having a bit of trouble understanding how this all works lol, any help is greatly appreciated

 

How much boost the blower can produce depends on many variables.
* Cubic inch. The larger the engine the less boost it will make with a supercharger.
* Headers and exhaust. A better flowing system will produce less boost, requires a smaller pulley to regain the loss in boost. Ultimately though, more power will be gained.
* Camshaft and heads. A camshaft with some overlap will leak out some boost through the valves. Better flowing heads react a lot like a better flowing exhaust system.
* Altitude. Elevation plays a big part in how much boost is produced. Those people living in the higher elevations have to spin the blower harder to see boost.
* Condition of engine. An engine with real good sealing rings will ultimately produce more boost than one with worn rings.
* Rpm. An engine that is spun up higher in the rpm range will normally produce more boost.

Hope this helps. Bob

 

p1 of d1 , your running the 6 rib setup , you will have a hard time making boost and not getting belt slip

 

I agree, I wouldn't go any smaller on the blower than 3.00", even that is pretty small. I would go with a bigger crank pulley to get more blower rpm and boost.

 

What size crank pulley would you suggest?
Any thoughts on my theory that %change in impeller rpm would be about equal to %change in boost?

 

http://shop.brutespeed.com/ATI-1GJ11...-1GJ115-08.htm

Take a look at the eight rib upgrade, which uses a 7.65 crank pulley. The smallest ProCharger eight rib blower pulley is a 3.4.

To determine the impeller speed, the following formula is used:

Maximum impeller speed = crankshaft pulley diameter (N1) divided by supercharger pulley diameter (N2),multiplied by the step-up ratio (4.10 for the P-series/D series - 5.40 for the F series), multiplied by engine rpm at redline.

The P-1SC and D-1SC have a 62,000 rpm redline. Bob