After researching this topic endlessly and finding ridiculously inconsistant info, i decided to start my own thread.

Feel free to contribute info on collector diameters for any headers you think are relevant. Please only post info that you have verified...ie. measured personally or have the picture of it being measured.

the first here is my '95 JDM gsr header OD 2 1/4" X ID 1 3/4


next up is my '94-'99 greddy gsr header OD 2" X ID 1 7/8


and if anyone cares, a 1990 integra b18a header OD 2" X ID 1 9/16+"


Now what i'd like to know...

All USDM headers are supposed to have 2" OD collectors (2" doughnuts). So What is the ID of the US gsr headers. All the OEM headers seem to have the anti-reversion chambers, cutting down the ID, compared to aftermarkets with the same OD.

Here some info from SMSP about ITR headers (which is true)...

The DC JDM has a 2.50" OD x 2.37" ID collector.
The JDM ITR has a 65mm (2.56" OD) x 55mm (2.16") ID collector.

The ID on the ITR JDM is smaller due to the anti reversion chamber in
the collector and is actually a little smaller a couple inches in from
the end of the collector. The JDM ITR has 43mm (1.69") OD primaries
(I don't know what the wall thickness is) and the DC JDM has
1.75" OD x 1.62" ID primaries however the DC JDM primaries are a little
longer than the JDM ITRs.

 

i can look at my stock b20 header tomorrow mornin if ya like. i dont think theres a huge difference in the stock non r headers

 

nice info

 

I had a cast type r ex manifold w/2.5 collector. Im not sure what year or if it was usdm or jdm though, but anyways it worked great and looked bone stock.

 

throw that b20 header in too. Remember guys, measured at the open end - inside diameter, and outside diameter (doughnut size). Any honda header.

d

 

i have a stock LS header on my b20 now but soon i should have a 10-94 with full 2.5" setup


Ok well heres the b20Z header, i had a b20b one also but i threw it away.

inner collector diameter is 1.5" outer is 2"
ports are 1x1.5"

on a side note i took a picture of how horrible the ports are. theres a weld that sticks in 1/4" on each side (done for strength i know) then a gap and then the pipe is in there with a smaller diameter. it looks awfull for flow.

 

posted by IN VTEC...

JUN 4-2-1 for Integra Type-R

2.577" OD
2.456" ID

and posted by au-gsr...

comptech
od 2.1"
id 1.8"

 

well JC, it looks like honda didn't want their b20s to breath any better than the old ls engines.

d

 

great info

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by daver &raquo;</TD></TR><TR><TD CLASS="quote">After researching this topic endlessly and finding ridiculously inconsistant info, i decided to start my own thread.

Feel free to contribute info on collector diameters for any headers you think are relevant. Please only post info that you have verified...ie. measured personally or have the picture of it being measured.

the first here is my '95 JDM gsr header OD 2 1/4" X ID 1 3/4


next up is my '94-'99 greddy gsr header OD 2" X ID 1 7/8


and if anyone cares, a 1990 integra b18a header OD 2" X ID 1 9/16+"


Now what i'd like to know...

All USDM headers are supposed to have 2" OD collectors (2" doughnuts). So What is the ID of the US gsr headers. All the OEM headers seem to have the anti-reversion chambers, cutting down the ID, compared to aftermarkets with the same OD.

Here some info from SMSP about ITR headers (which is true)...

The DC JDM has a 2.50" OD x 2.37" ID collector.
The JDM ITR has a 65mm (2.56" OD) x 55mm (2.16") ID collector.

The ID on the ITR JDM is smaller due to the anti reversion chamber in
the collector and is actually a little smaller a couple inches in from
the end of the collector. The JDM ITR has 43mm (1.69") OD primaries
(I don't know what the wall thickness is) and the DC JDM has
1.75" OD x 1.62" ID primaries however the DC JDM primaries are a little
longer than the JDM ITRs.</TD></TR></TABLE>

If anyone is interested,for the jdm dc you can use a donut gasket from a 95 dogde neon.its 2.5 inches and it will fit the dc jdm collector.im redoing my prelude dc header secondary and my new collector is gonna be 2.5" od.the gasket only costed me 11 bux from autozone.

 

The 2.5" donut gasket I bought from Hybrid Garage wouldn't fit my JDM DC 4-1. Pushing it on by hand wasn't doing any good. I tried filing the inside of it then tapping it on gently with a hammer and it wound up breaking. A friend of mine gave me a beefy Dodge donut and it went right on.

*edit* I even tapped around the edge of the collector to make it smaller and the H-G gasket wouln't go on.

 

cool thread, hope more people add to it.

RSR - 94-95 GSR
OD 2" IN 1 7/8"

 

Yeah I have measured the diameter of the collector end of the DC Sports JDM and it was 2.5" and the JDM ITR was smaller, it measured 2.25" thought it was interesting to see that the JDM DC 4-1 was bigger. didnt make any sense since they were suppose to be exact copies.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by QuanKwan &raquo;</TD></TR><TR><TD CLASS="quote">Yeah I have measured the diameter of the collector end of the DC Sports JDM and it was 2.5" and the JDM ITR was smaller, it measured 2.25" thought it was interesting to see that the JDM DC 4-1 was bigger. didnt make any sense since they were suppose to be exact copies.</TD></TR></TABLE>

the jdm ITR does have the same OD as the DC, its the ID that's different thanks to the anti reversion chamber.

I'd like to hear an explanation of the merit of these chambers. Honda seems to think they're important. I was reading a thread where some dude was saying that in "the great header test", the Oem itr header had a smoother curve than the DC one. Wondering if its the chamber.

d