yo rob ,
from what i have heard if ya get a decent header and a full system, you do get an increase but torque some times lags in the lower rev band due to less back pressure but then above 3k rpm -- 4k rpm you willnotice a slight difference, oviously gts will have a much higher gain i have a gt and have looked in to it. around 5-10bhp from standard ive heard,but thats with typhoon, 4-2-1 manifold,sports cat and scorpion full system (tuner5).
when i have the cash i will splash out on all of the above, except for the typhoon,got it already and it sounds awsome raws like a bitch!!
