7 inch crank pulley worth it??

[PaxtonBlown306]

ok, so ive been thinking about going with a 7 inch crank pulley, to try bringing the boost in a little quicker, and once again try to achieve the 14-15psi range.

Current setup is 2.75/6.87... making 11psi. I know the 8 inch is "the way to go", but id be spinning my blower to crazy RPM and making way more boost then i want with a 2.75/8.00 setup, so would the gain's from going to a 6.87 to a 7.00 be worth it? Would i gain any boost?

[Chuck]

I think most of your problem must be slippage. I put a 2.75 blower pulley on my S trim and it was making 13#'s at 5000 rpm. I didnt get to see what it made at 6K cause there was coolant everywhere, I blew both headgaskets.

Are you using a blower brace of any kind? Is this with the stock Vortech tensioner?

I use the SCH bracket set up and there is nearly no slip, though the bracket is currently unavailable there are other ways to stiffen up the brackets and get more force on the tensioner.

[PaxtonBlown306]

im pretty sure there is no slippage. I can watch the boost guage show it start building boost... pull right to 11lbs and stay there til i shift. If it were slipping, wouldnt it pull to 11, then drop off?

Im using the stock tensioner with one of them billet tensioner things. I also have a fairly long belt, and alot of tension on it, so there is pleanty of belt wrap on the pulley.

[regattacoupe]

maybe try the 8" crank and the 3.125 or 3" blower pulley. Thats a pretty awesome setup.

[BLOWNBY]

im pretty sure there is no slippage. I can watch the boost guage show it start building boost... pull right to 11lbs and stay there til i shift. If it were slipping, wouldnt it pull to 11, then drop off?

Im using the stock tensioner with one of them billet tensioner things. I also have a fairly long belt, and alot of tension on it, so there is pleanty of belt wrap on the pulley.

You have to have have slippage. You should see more boost than that with those size pullies. Just because it is slipping doesn't mean you'll have boost drop off, especially in the 11psi range. Here's what you need to do. Your 2.75 & 6.87 @ 6,000 rpm = 51,723 blowers speed. Get an 8" & 3.33= 49,729. Put a torque wrench on the tensionor plate and crank it down to 85lbFT. I bet you'll se a lot more boost.

Or keep your 6.87 & 2.75 and torque it down to 120lbft. See what happens.

[RSNovi]

I heard Bob Kurgan say that the Renegade guys use as much as 300 lbft of torque on their belts.

[BLOWNBY]

Yeah I've heard the same. CRAZY Tight to the tune off F#("F" sharp)


I have found the above numbers to be pretty good for this s-trim setup and those boost numbers and pullies. No need to over do it on an s-trim with 11psi!!:freaks: I know your not suggesting this!

But a lot of people think it is tight, when it really isn't. I too made this mistake. Best to use the toque wrench and find out what works. Then you'll be sure it is tightened consistently every time. Plus you'll know when and if the belt is stretching. A lot of times you'll lose 20 lbft form a little driving in the belt stretching, even when you think it has been streched out.

[PaxtonBlown306]

Or keep your 6.87 & 2.75 and torque it down to 120lbft. See what happens.

That much tension isnt gonna put alot of stress on the bearings?

[RSNovi]

Yeah, I tighten mine until I think it is tight. Then I give it a few more turns on the tensioner for extra good measure. My belts stretch a ton after the initial install. I used to replace the belt every race since they would stretch so much.

[BLOWNBY]

That much tension isnt gonna put alot of stress on the bearings?

Not really. It is a lot but would be o.k. I would get the pullies I suggested. The point is if your going to run those small pullies you need to put the torque to it. Try it till you get the new pullies and see what it does for your boost.

[RSNovi]

Check this thread out. It was interesting reading:
http://www.midwestmustangassociation...7420#post37420

[PaxtonBlown306]

Not really. It is a lot but would be o.k. I would get the pullies I suggested. The point is if your going to run those small pullies you need to put the torque to it. Try it till you get the new pullies and see what it does for your boost.

Ill try 110ftlbs on the tensioner and see what happens with that. I dont want to buy another blower pulley, just so i can run a 8 inch crank pulley. Maybe when i switch to a YS-trim i will dive in and get a 8 inch with another blower pulley at the same time.

But i still dont think my question got answered.... will there be any gains with the 7 inch crank to be worth the money spent?

[regattacoupe]

Ill try 110ftlbs on the tensioner and see what happens with that. I dont want to buy another blower pulley, just so i can run a 8 inch crank pulley. Maybe when i switch to a YS-trim i will dive in and get a 8 inch with another blower pulley at the same time.

But i still dont think my question got answered.... will there be any gains with the 7 inch crank to be worth the money spent?

I don't think so. You're really not gaining any blower rpms(very little) and it's not gonna grip any better than a 6.87. Now the 8" crank is grip city, and you gain alot of low end. ;) Just something to think about.

[BLOWNBY]

Plus I don't think the little extra you will spin the blower will increase your boost. This is not your problem. It is slippage. An it is slipping on the SC not the crank. You either need a larger SC pulley or a lot more torque. The 8 " will allow you to run the larger SC pulley and spinn the blower near the same speed.

[glenn95gt]

Plus I don't think the little extra you will spin the blower will increase your boost. This is not your problem. It is slippage. An it is slipping on the SC not the crank. You either need a larger SC pulley or a lot more torque. The 8 " will allow you to run the larger SC pulley and spinn the blower near the same speed.

what about for the 94/95 setup? They don't make an 8" pulley for our cars. What setup do you recommend for 15lb of boost? I have the 7" crank pulley and a 3.33, and a 2.87 SC pulley..