CoolGuy094

Because I never had any belt slip issues with my 3.2" pulley.

surferboy120

That's good to hear I am not sure there are a lot of people that can say that with blower pulleys at or under 3.6. Is your pulley setup all stock or some aftermarket magic like special pulleys or so forth?

CoolGuy094

No, standard Comptech kit stuff... crank pulley and tensioner were the standard Comptech kit, SC pulley was the standard 3.2" one from SOS. Belt was a standard Dayco from Autozone. Spun it to 9k all the time, no signs of slip like drop-off of boost up top or belt residue under the hood.

surferboy120

I am surprised to hear that but awesome for sure.

s2000Junky

I never had any belt slip issues running a 3.2 on a 1200. You would be more apt to getting them on that blower vs the 1220 even, due to the added hp/spool up rate. There will always be some slight loss in 1st gear just because of how fast it revs at WOT, but your breaking tire traction anyway so it really doesn’t have any negative net effect on performance. 2nd gear up is what counts. 1st gear is useless at these power levels in WOT.

DaGou

size matters but it is the ratio between the two pulleys that counts. It is about contact surface, belt angle, belt wrap. Think of two pulleys the same size for a minute. The belt wraps 180 degrees around each pulley. Back to our pulley arrangement. It does not matter if you make the smaller pulley smaller or the bigger pulley bigger it has the same effect. By changing the ratio you introduce just as much belt slip as changes to smaller SC pulley. What did you think that you some how can cheat the the law of mechanics and you were the first person to figure this out? Using a 3.8 with a 6.5 is like your 6" with a 3.5. With a 3.5 belt slippage is doubtful so you should be fine. Chart below compressed, first column is SC pulley size the next three are crank pulley sizes, it just shows the ratios between the two sizes.

5.45" 6" 6.5
4.8 0.881 0.800 0.738
4.6 0.844 0.767 0.708
4.4 0.807 0.733 0.677
4.2 0.771 0.700 0.646
4.0 0.734 0.667 0.615
3.8 0.697 0.633 0.585
3.6 0.661 0.600 0.554
3.4 0.624 0.567 0.523
3.2 0.587 0.533 0.492
3.0 0.550 0.500 0.462

surferboy120

Its all about belt wrap. A larger crank pulley will spin the blower pulley faster and give you better belt wrap (less slip potential). This allows you to up the boost without going to a smaller blower pulley and potentially introducing belt slip.

Two ways to spin a blower faster. Smaller blower pulley or bigger crank pulley or a combo of smaller blower pulley and larger crank pulley.

This 6.5 crank pulley with 4.1 blower pulley makes basically the same boost with better wrap then the next 6.0cp \ 3.8 blower pulley example


6.0cp \ 3.8 blower pulley example


Also the above maps are for my specific blower which is the Vortech SI which produces higher CFM than other blowers and will not reflect boost levels of other makes and models.

pwrinxs

I run a 4.0 pulley on an AP2 with a Novi 1200 and get 8.3 psi max. Car dynos between 379 rwhp and 426 rwhp depending on type of dyno. I have a stock fuel pump right now. Do you guys think my setup can handle a 3.6 in pulley without any other upgrades than those I already have. I run ID1000s and a racing heat exchanger. What kind of power would I make on 93 pump?

BuggyofMildDiscomfort

5 inch pulley on the blower, AP1 with stock lower pulley, and it seems like it peaks at about 8-8.5psi, it's not mapped yet mind, so it's only been given WOT with no load, obviously don't know what power it'll make yet either.

edit: Eaton M112

LDfavoriteson

Pwrinxs
I run a 4.0 pulley on an AP2 with a Novi 1200 and get 8.3 psi max. Car dynos between 379 rwhp and 426 rwhp depending on type of dyno. I have a stock fuel pump right now. Do you guys think my setup can handle a 3.6 in pulley without any other upgrades than those I already have. I run ID1000s and a racing heat exchanger. What kind of power would I make on 93 pump?

I don't know what system you have but you I'm running a 3.6 or 3.4 on the SOS kit I'm at 435 hp. You may to upgrade your fuel pump though I'm using the walbro 255. So I'd expect you to be around 410-450 hp depending on the dyno on 93 oct