help finding right pulley size for supercharger (rotrex)

[blitzceli]

Im new to sc and pulleys ect so, im doing my research yada yada yada. I called w2wpowertrain and asked the guy does he know what psi each of their pulleys makes? He basically told me it is impossible and if I guessed and exceeded 12600rpm then the warranty of the sc would be voided. So here is where my questions come in.

I need to find the diameter of the crank pulley. Does anyone know what it is?

Then he suggested to find a pulley calculator and figure out a size pully that wont exceed 12600 rpm (limit of the c30-94 unit) I need to look at the driven pulley (sc pulley) and the drive pulley (crank). He also through in ratios which then confused me, He was like if you have a 1 to 1 ratio then and you rev the car to 8k then the driven pulley will be 8k, I understand that... But he lost me after that and I think he even confused his self aswell, because he paused for about 30sec then was like just look at the data sheet. So here are my questions


1. What is the diameter of the largest pulley on the car (crank)?
2. How do I determine the amount of boost that each pulley size will produce?
I know that a 105mm pulley will make about 8-9psi at 8500rpm, b/c this is what j factor told me. Im looking for 11-13psi basically and if I had to guess id say that a 100mm would be around that. So what size pulley would you speculate that makes 11-13 psi but wont exceed the 12600 rpm.

here is the data sheet for the rotrex c 30 unit

http://www.w2wpowertrain.com/images_w2w/contentPDF/RotrexC30_supercharger_range1.pdf

[Boosted2.0]

Just measure the diameter on the stock crank pulley and based on that we can tell you what pulley size you need to achieve a given supercharger RPM. *BUT* that may not tell you boost exactly, as the volumetric efficiency of your whole motor and the intercooler efficiency will determine the amount of resistance to airflow and air density which is what causes pressure in the intake manifold. (In other words if you have cams and a ported head you will make the same power at lower boost than on a stock head with stock cams)

[Boosted2.0]

a quick search shows stock crank pulley is 127 mm which would mean an 85.6mm S/C pulley would put you at 12600 RPM so thats your minimum diameter

[GT-StreetCrime]

J-factor did the math in his rotrex thread.

[The__J__Factor]

Sorry,
Max Impeller Speed of The C30-94 is 100 000rpm not 120 000rpm

and Max input Shat speed = 10 500 not 12 600

Crank Diameter =5.08 (of 2zz)
Blower Internal Gear Ratio =9.49
Max RPM =8300
Pulley Diameter =4 (ie 100mm pulley)

Impeller Speed = 100034.09 Rpm

Ill be using a 95mm pulley and over spinning it abit

[blitzceli]

Thanks everyone I figured out the calculations and found out the exact pulley needed to run roughly the psi desired.

[The__J__Factor]

sorry everyone i just edited my post above, please double check it to find the correct values.


Also Blitz wut pulley have u decided to use?
Its hard to estimate PSI coz boost builds in a exponential fashion more then a linear way.