Hi all, im just poring on behalf of a friend of mine, to see weather anyone has done extensive testing with GX exhaust manifold header pipe diameter and length etc etc. It is a race car so there are rules and regulations to abide by. It runs an a12 with h89 head on unleaded, standard a12 carby, 60thou oversize bore and a pretty tame cam. Im sure someone out there has done the dyno ground work and hopefully they are able to help out with some specifications. Im mainly after what length is ideal for the twin pipes and what diameter pipe, then what size do the collect back to, and for how long, and when in the equation will the hotdog muffler come (also regulation).

If there is any more info i can provide to help get a better answer ill try my best to do so. Thanks in advance, GG.