If nobody knows this or does, there is a vendor here in Tacoma (off of HWY 512 and Steele st) that makes pulleys for your cars.
www.pulleyboys.com
&
www.pfyc.com

Yep, got them on both of my Redlines...

Yep, got them on both of my Redlines...
Both?
one street one race?

No the wife drives one also, I wish though.

I actually helped a bulington guy from the redline forum put this on his car also. Just to throw it out there I have the puller and I am willing to help if anyone is interested.

Pulley Boys is making a tool too make it easier to change the pulley on the Cobolt/Redline/G6, real cool set up!!

yep and it works awsome.

how do you know what size is best and gives better performance
?

I saw on pulley boys web site that they claim the cobalt does not have enough room for the puller with the SC on the car. you have to remove it. is there anyway around having to remove the SC?

From what I have seen the ss is much tighter fit. But dont freak on the sc removal it is very easy and no headaches at all. I am running the 3.0" pulley on my car and the 3.2" on my wifes car. Some people are using the 3.0" on the stock tensioner and its a little to loose for me so I bought the zzperformance tensioner and it works great and can be adjusted for any size pulley.