ive got a GX head on my new motor with 42mm twin webbers, bored 40thou ect. ect. and am wondering what the standard GX exhaust manifold is like (two pipes into one sort of thing). I aslo have a two inch exhaust from there back with two hot dogs (no muffler). has any one changed this exaust manifold in favour of true extractors? and if so was there a noticible gain or change in rev charachteristics? and ultimaly is it worth doing?