Hey guys wanted to know if any of you could put your two cents in on this. I have ported heads, ported exhaust manifolds, custom exhaust, 180 thermo, cai, ported lim, ported throttle body, 3.5 pulley, custom tune. I had a friend of my tune the car with hp tuners and I am only getting like 5psi of boost on my guage. My vacuum is 20psi at idle and 10-15psi while driving. Is it possible when he tuned the car he could have changed something that would have affected the boost. The car runs great until wot and it still runs good but just not getting full boost. Also the two map sensors on the back of the supercharger, are they both suppose to have a vacuum line or just one.

First, vacuum is measured in inches of mercury. 20"Hg sounds right at idle for a stock cam.

Second, are the heads home ported or are they staged heads from a vendor? I could see staged heads increasing flow enough to drop boost that low, however if not something may be askew with the boost bypass valve.

I can post up an underhood picture of the MAP bracket later, once I'm at home. If your friend tuned the car, can't you go discuss this with him?

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'04 GP CompG - 2.6" junk

Only One of the sensors on the back is supposed to have a vacuum line, I have asked this before too How much boost were you getting before?

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It's possible the boost bypass valve is malfunctioning and if so needs to be replaced.

Also hot air is less dense than cold air so you will get less boost in the summer and more in the winter.

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Bright Red 2008 G8 GT

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