Why is my 3.70 pulley only giving me 8psi at 6200rpm???

06JET

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You can see what I have done to it in the sig below. So why am I only getting just over 8psi at redline? By looking at other threads I should be getting 12psi which I actually do not want. Stock internals shouldn't see over 10psi is what I'm told. Now I am wondering if my nGuage is reading accurately or if I am tapped into the right vacuum hose location. What do you think?
 

06JET

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Thanks, but I have checked for leaks and I don't have any that I can tell. Car runs great when under boost or not under boost.
 

46addict

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If you see any black dust (belt dust) around the pulleys that's a sign of slippage.

And what vacuum source is the boost reference line hooked up to?
 

06JET

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If I remember right it is taped into the brake booster line. I think that is the same line that connects to the fuel pressure sender. I am out of town and my pictures don't show the boost sensor after I hooked it up. NO dust around the pulley.
 

07 Boss

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Well those lopey NA sound cams are going to bleed boost. Boost is not a measure of power though. Are you making the right numbers? Given the same SC RPMs lower boost usually equates to more power as more air is getting into the cylinders. Less restriction. But cams with big overlap or smaller LSA is going to bleed some of that air right out the exhaust. I lose a little over a pound of boost with my little NSR cams and headers.
 

06JET

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I have not put it on the dyno yet. Just email tunes with Lund. I work out of town all the time and just haven't taken the time to set up a dyno session. The Detroit Rockers aren't as lopey as the Muther Thumpers it had when I got it but you make a god point. So 1-2 pounds of boost may be going out my exhaust? Even with that I should still be closer to 10psi with that pulley. It runs good and pulls hard so I guess the next step is the dyno.
 

07 Boss

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I have not put it on the dyno yet. Just email tunes with Lund. I work out of town all the time and just haven't taken the time to set up a dyno session. The Detroit Rockers aren't as lopey as the Muther Thumpers it had when I got it but you make a god point. So 1-2 pounds of boost may be going out my exhaust? Even with that I should still be closer to 10psi with that pulley. It runs good and pulls hard so I guess the next step is the dyno.

Yeah, my pulley on the Whipple is supposed to make 11.5-12 psi and I make 10.3-10.5 psi with my baby cams and exhaust. But HP numbers are right where they're supposed to be. Actually tuned it down a bit for safety.
 

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