customer brought in his 07 shelby 500 with whipple. Has svt tune, that was installed by another shop. Dynoed and test drove at 10 lbs boast. Brought it back to town and worked good for a couple of weeks. Then one day it was down to 6, 7 lbs. He says power is down some. He has installed new belt with no change. does not squeal... Can not find and vacumn leaks, valve a the back is closing o.k. (aganist the stop) . Problem is I have no specific knowledge of the workings of this system. Just know that it was working o.k. and now its not. Help. Thanks. DanO

I would probably check how the boost is being measured first. Try using a mechanical gauge tapped into the boost/vac line going to the fuel rail pressure sensor. Verify boost under WOT and then we can start trying to trouble shoot it. Jared

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Hello, first post, hope no one minds me making it here.

I have a dumb question, where do you live, and was there a dramatic Temperature / humidity change around this time? and do you have a pyrometer installed?

We did check it with onother gauge and it was on Also the power is down.
Also the temp/baro, corrected alt has be checked. My personal sc car stays the same within a 1/4 lb boast no matter what the weather is doing.??
Thanks for the replys, as we have not figured this out. Owner has calls into whipple. ??? Thanks Dano