Not a ton, the intake will yield you the highest gains and smooth out the power band and shifting a little, but a header is the most restrictive part of the exhaust. Can only expect a few ponies from other exhaust mods. Probably looking around 10-15 max gains for that setup without the header. Add a header and a tune and you'll be upwards of 40+ at the wheels with the Orange Virus (MTX), but those mods by themselves won't do a ton. The intake was the biggest bang for the buck I think on my car - really helped make 2nd gear not so pathetic, but the tune made everything better. Highly recommend.