So i was talking to this shop about putting a 2.5 in. collector on my H23 DC 4-2-1 Stainless Steel Header and they said that I wouldn't see that much of a gain from it b/c the DC hedaer is garbage b/c the secondary piping is smaller than stock. Secondary may not be the right term for it but the part of the header after it merges from 4 pipes to 2 and before it merges to 1 pipe. Is this true? I was going to make it 2.5 in from the 2 pipe merge to 1 pipe all the way to the cat. Who has done a collector mod to a h23 dc header, how much did you pay all together, and was it worth it? Also, does anyone know the inner diameter of the piping on the h23 dc header b/c I couldn't find it on DC's website.
(feel free to enlighten me on the correct terms for the different parts of a header while you're at it )

 

I am currently in the process of a H23 DC 2.5" collector mod. I am not finished and won't be for a while but I can probably get the specs you ask for. For the record you can bolt the H22 DC down pipe to the H23 DC top half. That is what I did in my case.

This is what I have got done so far, all in 304 stainless steel.
Custom flange I made:

Custom 304 O2 bung all with fancy TIG welds:



If you want to you can do what this guy did:
https://honda-tech.com/zerothread?id=1450668

He stepped the primaries up to 2" secondaries then had a 2.5" final collector. He is customizing his to fit an H22 in a CRX but it is along the same ideas.

Pirate

 

I knew you'd come through for me Pirate. Beautiful flange and welding. I haven't learned to weld yet so replacing the secondaries is gonna be expensive. $600 to make the secondaries 2" and 2.5 merge collector with 2.5 in. piping to the cat. For that money, I may as well have kteller make me a custom h23 header. I want to know if just putting on the 2.5 in. merge collector and 2.5 in. piping to the cat alone will be worth it (cuz the shop i talked to said it wasn't) and if it is what kind of gains can be expected. And why did you use a h22 downpipe? I'm assuming because it was just there or it was real cheap or am I wrong and the diameter of the piping is larger?

 

$600 sounds pretty expensive. The DC collector mod is not exactly proven so I do not know if it is better, worse or the same as the unmodified collector. Unfortunately my setup is pretty different than it was a month ago, so a comparison in my case is not real scientific. On the other hand you have the opportunity to forge new ground. It is after all, just a DC header and I would not expect an extra 20whp or anything since it is not exactly a quality example of custom workmanship, fabricated with your setup in mind.

Another thing is that I know for a fact that the DC header will support up to 200 horsepower on an H22. So unless you are shooting for big numbers on the H23, then you might not have to change anything at all. I think that the header modification is for people trying to reap the last few ponies from an inexpensive setup without shelling out for some custom expensive, and experimental that might yield mediocre results.

In my case, it cost me time and a 30 pack of coors light for the guy I know to weld up the header. Everything else I got for free or was excess pipe cut from the stainless exhaust kit I installed with the header. So it is cheap and easy to get the mod done to test it than go out and spend $1000 on a full custom header.

And I only used an H22 DC down pipe because I had one lying around and bolted right up to the H23 primaries. I do not think that it is any different for the H22 versus the H23.

Pirate