I got an 83 trans am that I just put a new motor in a couple months ago, Its a 305 ho bigger cam,compresion, edelbrock intake/ carb, no smog or egr. So im strarting to do the exhaust syatem I got a pair of hedman 15/8 headers and im going to run 2.5 inch true dual through stock routing into a pair of spintech pro street mufflers. how much horespower/torque will I gain from the stock sysem, thanks,Eric

Sounds like somewhere in the 30-40 range