Belt slip on Magnacharged LS1?

[streetk14]

I just got the new 122 Magnacharger running on the LS1 in my '67 Camaro last weekend. I've been driving it around with the Magnuson base-tune, and am trying to make sure all the bugs are worked out before I take it to the dyno.

I seem to be having a belt slip problem at higher rpms or in the lower gears where the rpm increase is very quick (1st gear especially). I am only seeing about 6 psi max on the boost gauge, and that usually drops down as I get to the higher rpm range. There is a noticable amount of belt dust on my accessory mounting brackets, so I'm almost 100% sure this is a belt problem. The fact that I'm losing boost is what makes me think something is wrong.

This is the larger, 122HH blower, and I ordered it with a 1:1 rear pulley drive ratio so that I could run a larger front pulley for better belt contact. It has a 3.0" front blower drive pulley right now, and I am running the stock f-body crank pulley. I have seem some similar engine combos with the 122 blower, and I was expecting to see around 10 psi with these pullies.

I am running a Street & Performance front accessory drive system, and am wondering if this is my problem. I did upgrade the tensioner to a very heavy-duty tensioner when I installed the blower. The tensioner takes a 3 foot breaker bar to compress, so it is by no means weak. It seems to put good tension on the belt, but I don't really like it's location in the system. I have tried several different belt lengths and I switched to a Goodyear Gatorback belt, which did not get rid of the problem.

The other thing I think it could be is the lack of belt-wrap around the crank pulley. From looking at pictures, my setup has less crank pulley belt contact than a factory GTO or Vette has. I tried to route my belt a more efficient way (to get more wrap around crank), but I could not locate the proper length belt to do that. Apparently, all the belt manufacurers have a gap in their sizing from 115-117". I need something aprox. 116" long to route the belt the way I wanted.

Mark @ S&P is sending me an adjustable idler pulley bracket that is supposed to replace the tensioner on my accessory drive. He thinks this will cure the problem, but I wanted to get some input from you guys. Here is a picture of what my belt drive setup looks like. This is what I have, except my tensioner is slightly different.

What do you think?

Andy