i have heard of the heat issues, and do not want to go that route. i also understand that free flowing the exhaust will help, but how, where do i get better, larger manifold pipes. yes i may be able to persuade someone to make them, but they wont be CA legal. my exhaust shop tells me once he gets past the 02 sensors its fair game as long as it has the cats and muffler.
??? I'm in the same boat too. discountconvertrs.com has the high flow cats with the front pipe/O2 sensor bung, but I haven't found anyplace besides OEM for the actual pipes off the manifold (headers?). I am trying to get some quotes for a complete custom job from manifold back (front pipes to dual inlet high flow cat, single out to flowmaster) Trying to tuck it all up and out of the way and open it up a bit.
The manifolds look pretty good, but there is definetly some gain to be had in the down pipe (manifold to cat pipe) as well as the rest of the exhaust. The trick will be to make them appear stock, and keep the O2 sensor the same distance from the manifold. Probably some nice mandrel bent pieces of 304 stainless could be used to form something close. The 304 will brown a bit over time, and thus look stock. It will reduce underhood heat issues as SS transfers heat roughly 200% slower than regular steel.
I'm waiting for my buddy with his FJ62 to lose his exhaust so we can build a nice stainless system for it from the manifolds back. You ready yet, Lou?