I have:
JDM B18C, OBD1
1999 Civic LX with 99-00 Civic SI Engine Harness
I have used a P28 Chipped, but currently in there now is OBD2 GSR ecu

Thought the header was JDM B18C header but it does NOT look like what it's supposed to
What caught my eye was how small the catalytic converter looked.
After removing the cat, I was surprised at house small the collector ID is on the header.

I measured this to be Ø1.550" (probably supposed to be 1 & 9/16")
I also measured the cat inlet and outlet ID's both at ~Ø1.835

Later today I'll remove the heat shield and take a photo of the primaries from the engine bay if that will help
What header has a collector size this small? Doesn't seem like it belongs on a GSR.

I actually feel like the car dies out after 6,000 RPM, could this very well be the reason it feels that way?

Thanks all

 

looks like a gsr from the bottom but cant really be sure. could be a LS manifold.. If it feels it dies out after 6k sounds like vtec is not engaging!

 

IF it is a GSR manifold, it would have to be a newer one... '94-99 GSR manifolds do not have the O2 sensor bung in the manifold. It is actually located just behind the mouth of the cat. Since you said it is a JDM B18C (GSR), it is likely that you have an LS manifold instead. Either way, the outside diameter of the collector is only 1 7/8" in diameter, and if you have an inner pipe, it will make the collector smaller.

 

When I was running the chipped P28 I thought that vtec may not be engaging, which is part of the reason i then installed a P72 ECU to show me any fault codes that OBD1 wasn't bringing up. The only thing that came up is the Seconday O2 sensor heater, which as you can see this doesn't have that because the installer just went OBD1. The car felt the same with either the P28 and the P72 ecu's.

What brought up my original question is, I'm going to convert to OBD2 but getting an OBD2 Cat, a secondary O2 sensor, and wire in the sensor to the ECU.
I just wanted to know if this header is bottlenecking a stock GSR and if I'm replacing the cat I might as well replace the header as well. I don't want to drop a few hundred on an aftermarket header if that doesn't end up fixing the issue.