i had to modify the greddy due to the fact i never had a piece of the exhaust that was approximately 9 inches long that had the 02 bung for it due the to aftermarket oem exhaust manufold that had it built in...so they were actually right on the dot for oem specs except for that.....do some more research and youll find out thats how it was made....so instead of askign and asking the same question bout header/exhuast set up....read up