Primary lengths in multiples of 10"-12" looking for 32" to 36" to the collector if you have the room and can stand the complexity.  Ceramic coated inside and out would be good. Heat wrap makes an astounding difference. You can touch the exhaust while the engine is screaming. The race car is not drivable without heat wrap on the muffler. The interior sheet metal turns from white to brown with paint blisters. We run heat tape and a shield over  a 4" ID stainless packed Borla.