Well I installed the stainless steel bov spring today after reading reviews here and on cobalt ss forums (some good, some bad). I've been driving my HHR SS almost every day since I got it 2 weeks ago, and I can tell a difference. I'm not saying it makes more power, but it does feel like it makes you hit boost faster/harder. Overall the car feels much more crisper when getting into boost. I've only done 1-3rd gear pulls as I live in the city, so I can't vouch for 4th and 5th gear yet.

The stainless steel spring is easy to install but holding the bov with it in and closing it to start the bolts is a mofo. There is a huge difference in spring tension between the factory bov spring and the stainless steel bov spring. If your going do this, read the reviews both for and against it. To me a 10 dollar spring with results people were getting and out weighed the speculation (did not see the negative effects proven any where, just theory) of the negative effects.

I'm not claiming to be a expert with boosted cars but I'm relatively familiar with boosted cars, owned a gn, 90 talon tsi awd, and currently building a summit awd 5 spd wagon turbo vehicle.