: Techical Q about pulleys

07-17-09, 03:21 AM
So, i got my new tranny to work with w4m tune again. Thanks Jesse!

Now on to the next mod. I understand the need for more airflow into and out of the engine. So, cai and exhaust updates.

What I don't quite get is the pulley thing. The goal is to get the blower to produce more boost pressure. So I understand changing the pulley on the blower to a smaller one, so it will spin faster.

But why do you have to change the crank pulley? And how does the crank pulley change produce better hp/tq at lower rpms, where as the upper pulley adds more at higher rpms, or so I was told. Don't they both not simply result in more boost?

And doesn't changing the crack pulley also change other functions on the car such as A/C and alternator?

And last, why does one pulley change requires the w4m pulley tune, and the other one doesn't?

And at what point do you need to cap of the blower P valve? And is it completely blocked or is the escape pressure set higher?

Sorry if it might sound like asking basic questions, I just like to understand the technical reasons behind them better.


Gotham CTS-V
07-17-09, 09:04 AM
Thanks for posting that. I would like to have these answered as well.

07-17-09, 11:40 AM

The faster you spin the blower the more boost it makes. In return, it makes more horsepower.

So by replacing the upper pulley, or the lower crank pulley, you are modifying the blower rpm.

The crank pulleys are a 2 piece design. The Blower runs on its own pulley ring, so it is the only thing that is changed, so you dont have to worry about other parts on the motor spinning faster.

The mods that require tuning are only ones that i cant incorperate into the first base tune. After a point, the boost levels are too high for me to put into a general tune, so then i have to tweek it farther to make it more accurate for that specific boost point. It is basically boost level dependent for that. 12 lbs or higher. Which stock is 9.

07-17-09, 11:41 AM
The p valve is a secret backup for blowing off boost when you exceed a set level, so you cap it to let the car have full boost. It is needed past 11psi

07-17-09, 02:59 PM
Hey Jess, did you do that to my car when you put everything on or is the P-Valve something I need to do? Thanks!

07-17-09, 04:39 PM
No this is something i always do on any car i see. :)

07-17-09, 04:58 PM
Sweet! Thanks! Hey that engine overheating message I was getting wasn't the hose leaking like I thought, it was the gasket around the thermostat housing. I took it in to the shop and they fixed it for free! haha!