My SS has been driven from 10 degree weather to 85 degree weather and I ALWAYS see 15 psi max. Is the 15-21psi boost based on atmospheric conditions and air temps that GM claims another urban myth?

 

Well, if it ever gets warm around here, I let you know...

Isn't the cooler air more dense therefore offering a higher boost or doesn't it matter?

 

Cooler air is more dense so you see lower boost.

 

Take your HHR for an extended trip to elevations above 8500 feet, and take the mountain passes at 70+, you'll see 21# of boost.

 

I've noticed around 20-ish lbs of boost usually when I've floored it. Weather here varies from high-60's to high-90's. Usually though if I'm flooring it I'm more focused on the road than the boost gage. Typically I am driving at elevations from 0-1100 ft.

 

I still have not figured out the parameters that control boost. The most noticeable difference is in first gear, where sometimes it is 6 lbs, and sometimes 12 lbs. Second gear and higher is almost always 15 lbs max, but I see up to 18 lbs occasionally. Does not seem to consistently relate to outside or coolant temperature, or altitude to 4800 ft so that only leaves intercooler temp (maybe?). Agree that 21 psig at very high altitude is likely correct.

 

hitting passing gear from about 60 or 65, it did jump up to 20

 

Ive only hit 15 psi myself (100 Kpa in Canada ><) but I also live at sea level not sure if that has anything to do it with it, but it hasn't become very hot here yet either.

 

The boost is lowered in first (a lot) and second (a little) gears from what I have experienced first hand and heard from other members. I believe that 18+ pounds of boost (for any worthwhile length of time) will probably only occur under high load, and high altitude. I also suspect (from my own experience) and from other members (including gxp/redline forums) that you may see high boost like that in the first few thousand miles then the computer will hold you back once it learns.

 

With the ECU's in these cars they don't really care what boost levels they make they shoot for a target air mass / torque and it uses whatever amount of boost it takes to make that number....moral of the story boost is just a number....no matter what the gauge says you are still making the same power.