Originally Posted by sleepyboy
Very nice, I hope your not planning on using that factory exhaust manifold are you? It'd be best that you get a long tube and chop it up to fit the RWD chassis or make your own header. That stock one flows like poo.
Within the performance and rpm envelope we're working in, there's probably not 5 hp difference between a stock header and an aftermarket shorty. Eventually we'll probably make our own or make an adapter for the 1.8 Miata header. The bigger gains will probably come from selecting good mufflers and pipes.
There are also some British RWD headers available but shipping is really a deal killer. The design we'll follow is tri-y with 1-4 and 2-3 each paired, then those will feed another merge under the car. Similar to the obx above as well as the SVT headers.
But the stock ones will be easy to work with for now and should provide good enough performance.