hi all, im looking at changing the exhaust manifolds on my bmw but i cant find any exact info. is it actually worth changing the stock ones, do you get much if any hp gains, are the stock ones restrictive? my one has the cats underneath the car and not on the manifolds. i have seen a few pics on the net and the face plate on the manifold steps out (not flush) with the head ports so was wondering if it would be worth just porting the exhaust manifold to match the head allowing for better flow.
any advice would be appreciated as i dont want to spend out loads of cash for no gains!!