lbm13186

iTrader: (4)

Hey guys,
so iv been thinking about switching pulleys on the procharger. The pulley that i currently have on it is 4 5/8" w/ a ati harmonic balancer and I'm making 13# of boost (317 heads). Mods are listen in my signature. I was wondering what size pulley would make what? was thinking about going to a 3.7" or a 3.5" and was wondering how much boost to expect by changing it?

I also have a j bracket and I'm wondering if i switch to a smaller pulley how small can i go w/ out getting to much belt slip?? i would prefer not to spend $700 on a aster bracket rt now so ill might just have to wait on changing the pulley. Also don't wanna lift the heads either (don't really know how much boost that would take w/ ARP's??)

thanks guys

9sectruck

iTrader: (9)

every tenth on a pulley is 1psi. so it should calculate
out to 4.5 down to 3.7 should be 8psi increase

9sectruck

iTrader: (9)

with the added boost depending where timing is now you may need to lower timing to keep the heads down.

Firehawk441

iTrader: (41)

F1 has a 5.40 gear ratio. Make sure you do your rpm calculation before choosing too small of a pulley. With an F1D, 400 cubes, 4.25"/ 7.5" pulley combo I've made 15 lbs. at 6000 engine rpm.

lbm13186

iTrader: (4)

Can you clarify what you mean by rpm calculation?

thanks guys, think I'm going to have to wait until i can buy a aster bracket b4 i pulley down.

NitrOmm

iTrader: (1)

You want to be sure to spin your blower at a safe level of RPM.
If I'm not mistaken the F1A limit is 74k rpm. See below for the formula to calculate blower RPM of an F serries (when you plug in your pulley sizes).

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.

lbm13186

iTrader: (4)

thanks man will keep that in mind when i pick.

Bob@BruteSpeed

iTrader: (16)

I wouldn't go any smaller on the blower pulley until you switch out the bracket and intercoolers. Bob

ramairetransam

iTrader: (18)

i have a 4.25 8 rib for sale if you need it for any reason .

stage274

I agree with Bob, not to go to a smaller pulley set up, due to the belt slip issue. Here is what I have done, my f1a blower in not on yet, but soon. I have a 5 in pulley with the cbr 8.65 crank pulley. That puts me around 60k blower Rpm at 6500 engine RPM. I am expecting 15 lbs or so. Which still has to be determined.

The pulley I am using is freaking huge, and the reason I can run such a huge pulley is because of the CBR 8.65 crank pulley. So others here said they are seeing about 15 lbs at 60k blower rpm. I am not sure yet. I may see more, because my heads are not ported, and I run a stock exhaust from the y pipe back. I also run a stock ls6 cam. My goal is 750 rwh, with the torque not far off. However, I wanted my car to sound and drive stock, with stock type gas milage. If I did not get my ls6 cam for so cheap, I would have gone with BOBs blower cam. I may still buy that cam, if I can't hit my goal hp numbers.