[Nicks79]

Hey all, my friend has an 03 Cobra and it pullied (smaller) and the most he can get for PSI is about 4-5#. The setup he has should be good for 10-12ish. No leaks, good blower head, could it be the bypass? We cant figure out where is pressure is going. Of course, we are at almost 8,000 feet, would that make a difference? any help would be great!

[EagleAutosports]

Yes, altitude makes a difference. Does he have aftermarket exhaust parts like headers, off road mid pipes, and the like? Has he improved the air inlet tract with a CAI and bigger MAS? All of these can reduce the psi because when you improve the air efficiency, the boost will go down.

[Nicks79]

Has headers, has 90mm air intake... but that much?

[EagleAutosports]

Not sure how much but it could be up to 2 psi loss but have no decrease in power.

[88 Lx 50]

yea no way should he be losing that much boost no matter what altitude. if its a 2.76 or 2.8 pully he should be seeing 14-15 psi

[Nicks79]

So the only thing I can think of is the bypass... maybe its not closing or something

[Saleens281]

what was the last thing he added before the low boost? was it the pullies? maybe the belt is slipping

[lxarlo]

Originally Posted by Saleens281

what was the last thing he added before the low boost? was it the pullies? maybe the belt is slipping

good idea. there is a different tensioner you need to get to run the smaller pulley

how are you measuring boost? a mechanical gauge?

btw the 90mm maf is stock.

[paperchasn365]

and twin screw blowers or even roots style should see an increase in pressure when you open up the intake. Thats usually a weak point in factory supercharging. and if you put a smaller pulley on it, he should upgrade the idler pulley as well.(which could cause the belt slipage). The higher altitude will affect boost pressure because the air is drastically thinner.