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I have a d20...it loves the cossie header...it revs freely to redline and pulls hard to 6500rpm. Short of the loudness, you will love it. You have a d23 so anything you might lose on the low end will be less than I did, cause you have the torquier engine. I would say the primaries are just right. Not so big that it really matters.

the cossie header is a 2.5in collector and flexpipe, but it will mate up to 2.25in exhaust. I think magnaflow sells 2.25in. The loss between 2.25 and 2.5 will be negligible at these power levels. It will be loud, just go light on the throttle around police or anyone that will care. You will have a CEL cause the cossie header doesn't have two o2 sensor bungs. I just disconnected the second o2 sensor from the wiring harness and used the extension they provide to hook up the second one.

The way to get rid of the code is to get a tune for it, say from FocusSport as I did. The tune, header, intake, and exhaust properly driven with a 5 speed should be a 14second car of some kind...


Just some advice: you will need a 15mm ratchet and open ended wrench to install it and to tighten later. You might have to take your fuel stuff off the firewall (just unbolt it) temporarily to get the stuff in and out. You don't have to disconnect it. It is just a tight fit. The bottom mount for the header might be a pain to get the 10mm bolts back in. If so, you slightly smaller bolts with lock washers, larger washers, and nuts, and just tighten it up. This way it will be mounted securely and you won't have to fight it as I tried.
 

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As long as the flange is still there, it will fit.

You won't regret going bigger (cossie) on a d23.
 
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