Low boost pressure?
 

Hey guys,

I just bought a '06 cobalt ss supercharged and am loving it so far. It is completely stock except for an aftermarket muffler and tip. I have read that the factory boost psi should be around 12? My car is running at only 5 psi, maybe 7 psi when im really hammering it. any ideas what could be wrong? Im not even sure if the boost gauge is the stock one, it has an autometer sportcomp gauge. I know my way around an engine compartment but this is my first supercharged vehicle so please use simple words....lol. I dont have a ton of money to bring it to a dealership so Im hoping this is something I can fix myself. Any help would be greatly appreciated!

altitude playing a little bit of a role maybe
how many miles

It currently has just over 82k on it. Will the altitude really drop the boost pressure that much?

not altitude shouldnt do that low. first check your bpv which is the little black looking thing on the sc near the throttle body ........... Make sure the lines are good and there are no cuts. also make sure all vacuum lines are good and no holes. there known to be shit. if all good, check the internal compression!!

If Denver, CO is about 5280 ft above see level, you will unfortunately see a very low max boost pressure after supercharger. For example, here in Calgary the altitude is is about 3400 ft above see level and my full boost is a whole 3 PSI less than when I was living in a previous town near sea level. So you should go ahead and change the pulley to a smaller one. I would think that you could go to a 3.0 pulley without even changing the injectors, depending of course of your other modifications.

From:

Air Pressure and Altitude above Sea Level

At 5000ft (in Denver), the absolute air pressure is only 12.2 PSI (instead of normal pressure of 14.7 PSI at sea level).

At sea level, your supercharger (stock) is able to boost 12 PSI over the 14.7 PSI absolute pressure, giving a total of 26.7 PSI, which pressure is 81.6% more than the absolute pressure.

At 5000ft, the supercharger is still able to boost 81.6% over the absolute pressure, which absolute pressure is in this case only 12.2 PSI. So 12.2 x 1.86 = 22.7. If you subtract the normal absolute pressure at sea level (14.7) from 22.7, it gives only 8 (delta) PSI, which is I believe the maximum of what your pressure meter could show at this 5000ft elevation.

Hope it make sense.