What size crank pulley do you run now ?

Its a 12 rib 7.750 dia IF I remember right, Smitty

Any luck with this set up Smitty? What was the outcome?

I welded 5/8 by 3/4 or 1" ribs all over the head unit bracket, machined 1 1/4 or so spacers to the head unit bracket to try to slow down the flex. From doing this I was able to tighten the belt to death to keep it from slipping without pulling the bracket so hard it went out of alignment, still a compromise. I just fought with the belt slip issue on the dyno AGAIN a few weeks ago, My son put on the 64.5" belt with the 3.85 pulley which normally uses the 65" belt and just loosing that tiny bit of wrap absolutely killed our ability to make a pull without blower belt slipping, it was so bad that blower literally stalled to almost zero boost over 5000 rpms until we tightened it so tight I am convinced it would destroy the bearings and tensioner. AFTER coming back to shop with motor I realized this and I decided I am going to just buy a pontoon boat with a 25 hp, just kidding, but I did decide to address this issue further. I am going to bead blast the powder coating off the blower pulley to make surface less slippery and after much searching I actually found a source fpr a 12 rib belt other that procharger that is 66" long (1" longer). seeing how dramatic of a a effect that 1/2" of belt length made due to less wrap I bought a idler and am going to attempt to install idler to force longer belt to wrap around blower pulley signifigantly more, I will post pics soon, Smitty

Maybe it's time for an M4

My buddy had the same issues as smitty with his M4s. He added the idler as well. Fukin blower belt had to be a guitar string or it would slip.

I remmeber on the dyno, the engine was down a little power. Not crazy, as it was still making around 1200ish on 93 gas. My buddy, who owns the engine, and not really a huge gearhead, says he thinks the belt is slipping. We really didnt see any signs of slippage, or boost fall off anywhere. But he insisted we crank that belt tighter. So Mike T cranked it even tighter than it was, did another pull, engine picked up boost and like another 50-60hp!

This was a 12 rib setup on a M4 blow thru. We talked about going cog, but he said screw it, and bought some roots 10-71s and changed heads and what not.

I have a dyno sheet where my belt started to slip at 5700 right at 1200hp, you could see the boost fall off along with the power. I switched to a larger pulley and made another 172 hp at 6200.
I'm guessing the faster you spin them the harder they are to turn, I could be wrong.

You're PM box is full

Somewhat on the same subject. I have a friend that was having blower belt slippage and just tightened the belt tighter. After doing a long run the crank pulley falls off. As he looks at it he sees that the crank had broken. Had the motor rebuilt with new crank. One night he is showing another friend the picture of the broken crank. After looking at the picture for about 2 seconds he says. "Yep, seen this type of fracture many times, your blower belt was too tight" He then goes into explaining the difference type of fractures. This happened to a Ford forged crank.

This is a old thread that somone renewed, with the extra ribs on mount i have gotten consistent speed and boost but i am adding a idler to try to take some stress off everything