Here is the deal- on the dyno, my car makes 8 lbs. of boost @ 3000 RPM, then holds that through 6500. Never makes more than 8 lbs. Why?

 

Your belt could be slipping.

Check for black shavings on the blower around the pulley shaft.

Make sure that your pullies are EXACTLY aligned and that you have good tension on the belt.

 

Guido-thanks for the response- didn't notice any belt slipping, or evidence of it- I will check again. If it is not slipping, then what?

 

It seems really unlikely but you might check for a vacuum leak somewhere. You may have someplace where it is coming out and takes 8psi for it to happen. At that point it just wont hold any more.

Are you using a blowoff valve on your intake tract? It could be opening and letting air go by.

 

Guido-good point- I'll check the manifold for leaks, but the car does idle with no issues. I don't have a blow off valve on the car. Is the S Trim just too small?

 

I don't know much about the cent. blowers, but maybe the engine is using all of the air that is being fed to it so it doesn't make any more pressure that way. Again, I don't know. The other thing you could do is buy a tool that measure belt tension. There was a thread about that not too long ago and the guy had real good results with properly tightening his belt.

 

ATO Monkey-the DFI tuner told me is the engine moves so much air that the S Trim may be too small. I recently added Dart Pro 1 aluminum 72 CC, 2.08/1.60 230 CC heads, a custom solid roller. 296/306 & 658 I & 667 E, etc. The compression with the old 64 CC heads and cam was about 9-1, but I still only got 10 lbs. of boost.

The drive ratio of the pulleys if 2.38. Should it make more than 8 lbs.? Do I need a bigger compressor for my engine mods?

 

If you are in the market for a new compressor, I am looking to get rid of a Y/S-trim that is brand new. It is a polished head unit, with NO run time. And I can also hook you up with a set of cog pulleys to go with it.
BTW, with my 355ci. S-trimmed setup, I was only able to make 15# of boost with the charger running at max with a set of cogs. You may have run out of charger for that 39x ci. motor. My heads did not flow that well, and I had the TPI also.
Shoot me an e-mail, mabe we can work something out. Don B.

 

blownbird-thanks for the offer- I ordered the YS Trim Thursday on the Vortech trade in program. What are you asking for the cog belt set up? I am going to start with the v belt and see what happens.