I swapped from the stock 3.35" pulley to a 3.15" on my Procharger P1SC.
I'm running a 50mm Turbosmart race valve also.
Before the pulley swap it would only make about 5psi...now it's only making 6. I put a stiffer spring in the valve thinking it was pushing it open but nothing changed. When I let off the throttle fast the boost gauge will jump up to 10psi for a split second as the valve opens...the feed for the boost gauge is in the inlet piping before the TB.
I checked the gauge with an air hose and regulator and it's spot on. I also can't see any signs of the belt slipping (6 rib)...the grooves look brand new with no build up of any kind on them. Yes, the crank is pinned.
I checked every connection and all the rubber hoses in the system today and they're all tight and no holes, also checked the IC for cracks and it's good too.

I'm at a loss here. 5800rpm and 6psi is pissing me off. Any thoughts?

 

sounds like a belt slip issue to me. the 10psi spike when you let off the throttle is the belt grabbing when everything is slowing down to the same speed. does anyone offer an HD belt tensioner?

 

I'm using the Procharger supplied tensioner. The belt feels tight as hell...I'm almost afraid to crank it down any more but I could give it a shot I guess.
I just bumped the shift points up to 6000...gonna go see if that made any difference too.
If the calculator I'm using is right that should take it from 48125rpm to 49875rpm.

 

I think I found the issue. I took apart the tensioner screw and the brass bushing that slides inside the mounting bracket had dug into the mounting bracket and it wouldn't slide freely. It was bound up. I had to dremel a big burr off the bracket and added a washer between the bushing and bracket so it doesn't happen again. When I retightened the belt it got substantially tighter...I guess I only thought I had it tight before.
All I can figure is I didn't loosen that 9/16 bolt enough to let it slide when I swapped pulleys and buggered it up.
Road test coming shortly.

 

Do you have a spring tensioner?

 

Yes but the way it tightens is weird.

 

Get a new belt away. I have seen old belt do this alot.

 

Do you have a boost only or a vac/boost gauge? If the latter you really need to move the reference to the manifold behind the throttle body for accurate readings. The way you have it now, do you have the gauge reference between the valve and throttle body or between the compressor and valve?

 

Your boost gauge should be reading from the manifold after the throttle body, or from the brake booster. The spike is from the throttle body slamming shut and creating a quick jump on the gauge before the blowoff opens. You may be making more boost than you think. I also think 5800 rpm is a low reference point. Centrifugal superchargers make more power with rpm. Calculate your impeller speed, and you should be able to get an idea how much CFM your moving.

 

Boost only and it's between the TB and valve right where it should be.