Are you going with a smaller pulley JD? Any idea about what size I should get for mine? I think going 6 rib is best to try first. Thanks for catching that.
Yes it will get you close.
To figure pulley size from required boost level:
Step 1: Theoretical pulley ratio = ((14.7+Boost) / 14.7) x (engine liters / 2)) / Supercharger Size liters
*Assuming "0" inlet losses and 6.5" crank pulley.
For 6 psi boost with a 1.5L supercharger on a 4.0 engine: ((14.7+6) / 14.7) x (4.0/2))/ 1.5= 1.878 ratio
Step2: Supercharger pulley size = Divide the pulley ratio(1.878) into the crankshaft pulley size (6.5") to determine supercharger pulley size (3.46").
To figure boost level from known pulley size:
Step 1: Pulley ratio = crankshaft pulley diameter / charger pulley diameter 6.5" / 3.46" = 1.878 ratio
Step 2: Theoretical boost = (charger size in liters x pulley ratio) / (engine L / 2) x 14.7 - 14.7
Example: (1.5 x 1.878) / (4.0 / 2) x 14.7 - 14.7 = 6.0 lbs boost
The Eaton M90 displaces 90ci of air per rotation so that converted to liters would be 1.5 liters. I changed the examples above to reflect the engine and supercharger in this thread.
Pulley ratio 6.0" / 3.2" = 1.875 ratio
Theoretical boost = (charger size in liters x pulley ratio) / (engine L / 2) x 14.7 - 14.7
(1.5 x 1.875) / (4.0 / 2) x 14.7 - 14.7 = 5.97 lbs boost
Based on that you can estimate a rough gain of 90rwhp give or take. Of course how aggressive or how conservative the tune is, engine flow efficiency, camshaft specs, supercharger inlet flow efficiency, drivetrain losses, etc will play a sizeable role in determining your total number.
If I were you I would figure for 15-17rwhp. Twin screws and modern TVS make in the 18+ area but I don't usually see many Eaton's doing it according to my recollection. Use 15rwhp per psi and if you get more then be extra happy.
Im not going to be tracking this thing, I just want a vehicle thats more fun to drive. Im better off than I was, but I still dont exactly have an accelerating monster on my hands.
thanks JD, Ill look around pulleyboys for a 3.2 pulley then. yes, a 3 angle valve job was done to mate the si valves, along with some p&p. def better than stock flow.
Im thinking 8 lbs tops.
I just looked at pulleyboys. Confusing.
It does appear my pulley is 'keyed'. I just pulled the lock nut off to have a look at it. So factory for a supercoup (Depending on year, of course) is 8 rib, around 3.8" keyed pulley.
So, that means I need a 6 rib 3.2" keyed pulley. I dont see that anywhere on pulley boys.
What if I ran a 8 rib pulley on a 6 rib belt? Turnig in to to much of a junkyard build? I know, no one wants serpentine belt issues as the 1 belt runs everythnig. I wonder if I need to email pulley boys.
Had it that way for 5-years and no problems! 8-rib pulley and 6-rib belt.
really?i would think it would or could jump a rib and become off aligned with the other pulleys and cause it to pull off the other pulleys.
If the pulleys are aligned then the belt will not want to jump ribs because there is nothing pulling it out of alignment. Path of least resistance will make it stay on the ribs. It is not an uncommon thing to run a wider ribbed pulley than belt. My 8.5" crank pulley on my Explorer with the KB supercharger on it is a 10 rib but my whole serpentine system is an 8 rib. It works just fine.
Were going to find out.
At least I can run it and see what kind of boost I get. The pulley on the sc right now has taken a bit of a 'bang' on the ribs. Not too bad I don't think. It will be worth trying, and saving myself $100.00 though. Only paid $75+shipping for the whole SC.