would straight 2.5 exhaust be good for my cobalt like custom pipe from the stock manifold back? Because he says he wont be abe to bend the three inch on a cobalt so im just seeing. An do you think i will notice a lttle bit of horsepower diference from the stock exhaust

 

the difference between 2.5 and 3 inch in Grand Am competition when the 3 inch exhaust was taken away by the rules makers, was negligible. If you have really small pulley and a lot of mods it will make a difference, but for you , stock exhaust manifold I would go ahead with 2.5 and be happy, make sure you go to 3 inch at the rear most muffler if you can for the straight parts...good luck...

 

1.. Is it mandrel bent? If not, its pointless... The metal will be a smaller diameter at the bends causing flow issues..

2. If its not mandrel.. http://www.mandrelexhaustsystems.com...GNAFLOW/Detail <---comes with muffler as well for 255

3. if you want 3" - http://www.mandrelexhaustsystems.com...alt/Categories <-- You can pick with or without muffler.

Unless your around 300hp, or over, its been stated that youll actually lose power with the 3" exhaust.
with your setup, i think your close, but with the stock manifold, id only go with a 2.5", that will get you your best gains.