ITR header collector size

[Dave7CDMTYPER]

I've been researching and I'm trying to determine the collector size for USDM ITR header. Seems to be a lot of different anwsers. I don't have one so can't measure, but I have a JDM '96 spec, various aftermarket JDM headers, and a USDM Comptech.

Does anyone know for certain the size of the USDM header collector? I want to make sure so that I know it will connect to the USDM cat.

[aw614]

2.25in for US cars. I recall the CARB legal comptech header for the b18b1 and B18c5 is the same EO number? I do know the CARB legal header for the B18b1 that I used to have had a 2.25 collector and the OEM cat fit,

[oddomatik]

2.25in for US cars. I recall the CARB legal comptech header for the b18b1 and B18c5 is the same EO number? I do know the CARB legal header for the B18b1 that I used to have had a 2.25 collector and the OEM cat fit,

An EO number can cover multiple manufacturer part #'s, so I'm not sure that's a good gauge.

Example:

Screen Shot 2023-06-19 at 2.37.34 PM.png (568.5 KiB) Viewed 3121 times

All aftermarket cats I've seen for our cars are 2.25", so I believe aw614 is absolutely correct on that.

P.S. @Dave7CDMTYPER - I am still actively on the lookout for a stock header for you.

[GeHonda]

When looking at that outlet, there are two layers of metal. The 2.25" mentioned, I assume that is the outer diameter and not the inner diameter. Does anyone know for certain?

For example, in this photo I can measure 2.125" ID, but OD is about 2.375". This doesn't really clear up the confusion because it falls between the two.

ITR_Flange.JPG (137.66 KiB) Viewed 3115 times

[Dave7CDMTYPER]

This is my comptech header, which is currently installed and functioning fine on my ITR with the rest of stock cat and exhaust. The other is '96 spec JDM header that does not fit on USDM cat.

[Dave7CDMTYPER]

P.S. @Dave7CDMTYPER - I am still actively on the lookout for a stock header for you.

Thank you sir

[oddomatik]

Your pics don't lie... But you should maybe be measuring with calipers the OD of the pipe itself. The exact diameter appears to be hidden at the flange welds.

I think @coolhandluke nailed it here:

When searching eBay, 2.25" exhaust flanges exist... I think the OD of the pipe upstream from the flange is probably the best way to know for sure. I would imagine a 2" flange would be for 2" OD pipe, and a 2.25" flange would be suitable for... well you get it.

Here is another interesting thread with some more specific info that further adds confusion/matches what your pictures have shown.

[Dave7CDMTYPER]

Your pics don't lie... But you should maybe be measuring with calipers the OD of the pipe itself. The exact diameter appears to be hidden at the flange welds.

Thanks man, I'll try to measure more accurately including outer diameter. What we really need is for someone to measure their USDM ITR header that they are positive is USDM lol. Otherwise all these threads are kind of speculation. The JDM '96 spec header is confusing.

[oddomatik]

What we really need is for someone to measure their USDM ITR header that they are positive is USDM lol. Otherwise all these threads are kind of speculation. The JDM '96 spec header is confusing.

You're right. I'll be in there for a battery replacement in the next few days, I'll see if I can take the time.

[Dave7CDMTYPER]

What we really need is for someone to measure their USDM ITR header that they are positive is USDM lol. Otherwise all these threads are kind of speculation. The JDM '96 spec header is confusing.

You're right. I'll be in there for a battery replacement in the next few days, I'll see if I can take the time.

Awesome that'd be great.