This H22 header didn't fit on my 4th gen, the crossmember got in the way, they told me an aftermarket traction bar would make it fit. The guy who sold it to me last year told me to have gotten gains of about 21whp with engine mods and this header. I will fit perfectly on civics and maybe other models. Collector is 2.5 inches, it is ceramic coated and has a hole for the O2 sensor, what you see is exactly what you get, price is firm at $550 shipped. Paypal only please.