My stock 6# pulleys were a 6" crank, and 2.93" blower. The internal step up ratio of the PD is 3.05:1.

Impeller speed is RPM x ((crank pulley diam / blower pulley diam) x 3.05)

So if your redline is 6000, then the impeller speed you now have is 37,474 rpm. PD told me the head unit's redline is 43k rpm.

My 7" x 3.2" combo at 6,500 rpm then is 43,367 therefore I'm tapped out at 6,500.

I will go home and see what belt length is on the car tonight, I know it's a Kelly 7-rib, but I don't remember how long.

My car has ported TFS heads, SLP shorties/cat back, a 224/230 XE cam, 42# injectors with no FMU, and I use LT1 edit to tune it. The combination makes 5.5# of boost at 6,000 rpm, and I run it on pump gas with no knock retard.

Rog

 

Ok, good info on the step-up inside and the formula. Using it, it looks like a 6.75" pulley with the 2.93 6 lb pulley should let me take it up to 6200 (putting it at maximum [43k]). Normally I shift at 6000RPM, so that gives me a little room if I am late.

Also nice to know that I'm not near maximum right now.

-Ernest
95 Z

 

I wouldn't leave that 6# pulley on. find a 4# pully I'm sure alot of people that upgraded have them lying around. Your belt will slip with the combo you are talking about using. Someone posted a while back that they were seeing 9#s from their powerdyne with the 7inch crank and 6# head unit pulley so be careful 9#s is alot of non intercooled boost.

Jeff

 

Man, it seems like all the locals are coming out in one thread…

WRT the dyno vs track times… that doesn’t surprise me… my brother’s car (4 door LTD) has been turning out regular 120mph passes (even at 75&80… too bad they closed today) on a combination that has only dyno’ed at 326hp

To get the belts… try any car quest store (small car parts stores that belong to the chain, somewhat like most corner hardware stores appear to be Ace hardware stores even though it’s usually not in their name). They’ve been pretty good about getting any size 8 rib belts we’ve looked for…

 

Earnest,

I checked the belt size on my 7-rib combination. The lettering is worn off, but it is whatever Kelly 7-rib belt is closest to 42 inches. Looks like maybe 42.25". Definitely longer than a Gates 41.5" 8-rib because I have one of those in stock, and it's a little too short.

Keep in mind this is only the correct length for a 7.0" x 3.2" combination. If you decide to run a 6.75" as you've proposed, you will need to cut and try with the belt length unless you find someone whose done it already.

Rog