Just started tuning WOT. Running a D1SC with a 4" pulley that should be good for about 8-9 psi on my setup. However, everything starts off well, it makes boost about 4 psi around 4200-4800 rpms then it just dies off. At 5500, according to the datalog, the boost is at 0 psi. I thought it could have been spark plug gap and the BOV (Procharger Red Race Open valve) so I check the gap and reset them to .032 from .035 and checked the nut on the BOV which was loose and tightened it back up with 1/8" of the screw sticking out over the nut per yellowbullet.com instructions of adjustment. Did another run on a 10 degree hotter day and it made 4.5psi from 4200-4800 and then .5 psi above 5k rpms this time. Once it shifts, the boost comes back to 4.5 psi and all is well again until around 5k rpms. The boost flat lines and then looses all boost. A/F ratio was 10-10.5 so rich and I'll lean it out some but not too much before I fix this issue.

Now, that you have the background, here is question. I have a cold air box that I built. It has two 90* bends off the inlet side of the supercharger routing it to the front grill. All of the bends and tubing at 4" and the filter is a big 13" long by 6" round. The box is sealed for the most part and has one hole behind the headlight for fresh air and a small opening at the bottom of the grill for a tad more air. My thinking, the Procharger is running out of air thus flat lining at 4.5 psi and loosing boost above 5k rpms as it demands more air to build more boost.

Could I be right on my thought process? I'm going to test this theory this weekend but before I try just putting the filter on the end of the inlet and making a test run, is this a possible to loose all boost?

I don't believe it's valve float as I'm running AFR 8019 springs rated at 155 lbs on a closed seat.

Thanks for the help.

***Just an update...it was indeed valve float.

 

Do you have the crank shaft pulley pinned ?? If not then I would suspect that causing a huge issue. Next is take the air inlet tube off the back of the unit and try it. Report back..

 

What are those bends in your filter side piping made out of? If they're rubber you could also be sucking them shut and not getting any air into your charger. Or it could very well be a crank pulley issue as Mangled suggested. Just offering other ideas

 

might want to check the diaphragm on big red also , mine developed a hole and was doing screwy things with the boost.

 

What bracket?
Weak Tensioner?
Stretched Belt? (AKA to long, for tensioner to work correctly)
Poor Vacuum/Boost source to valve?

Last but not least, throttle staying open? Not some weird TQ table closing the throttle down? Its strange, but I have seen it happen.

 

That air filter setup sounds like a real power robbing design. First thing I'd do is remove it.

 

I also tent to agree about the intake design. id bet its being sucked closed.

 

Filter/tube thing seems unlikely to me. Are you sure the belt isn't slipping?

 

It depends what the tube is made from... most of us dont have serious vacuum in our intake tubes. I know it was a real problem for the side mount superchargers that moved the TB as well.

I dont see belt slip at that RPM with that size pulley and such low boost... but anything is possible. I never really had a problem with belt slip, but would that make him see 0 psi?

 

This is on a old school SBC with 88-92 Camaro TPI brackets running a 8 rib design. Datalog is at 100tps cable driven.

No belt dust detect. Belt is tight and brand new.