My JDM DC 4-1 just came in. I discovered that the collector (near the O2 bung) is actually 60 mm OD. Only the last piece where the donut lies on is 2.5" OD (63.5 mm). I think the JDM 4-1 is effectively also 60 mm OD because it's double walled near the donut. Maybe, that's why all japanese aftermarket exhausts like the Mugen are 60 mm OD.


[Modified by EuroITR1689, 2:03 AM 8/12/2001]

 

yep it's true about the i.d. ... someone posted about this before awhile back...

 

So, I think a 60 mm cat back should be sufficient. You don't need a 2.5" cat back with this header (and the JDM, Mugen etc.)? Don't know about the Hytech header......

 

2.5" (63.5mm) is the OD of the piping if i'm not mistaken... nominal ID of such piping is going to be smaller, so, 2.5", 60mm.... same ballpark.

D

 

D,

The OD of the end which has an anti reversion area is 2.5 but the actual
exh pipe inside as he said was 60mm OD. Which matches the OD of
said japanese exh systems.

 

Yeh. I am only talking about the OD, not ID.

 

Most JDM aftermarket headers for our cars sold in Japan are all the std 60.5mm which is 2.381inches
Which in it's self is not 2.5 inches unless maybe your counting outside dia.

2.5inches dia = 63.5mm

next std piping size seen alot if 70mm = 2.755inches

and if the outside dia is 60mm which is a dia of 2.362 in inches.

The actual inside dia is probably around 2.32-3 inches, but that just est...becuase unless you know the actual thickness of the piping they used..you can only guess at it.

 

aah, werd. i can't read very well these days....

 

Wow, lots of numbers in this post. Here are my measurements of the ITR JDM header.

ID of Inner Tube of Collector 2.160"
ID of smallest part of collector 2.118"
OD of outer collector tube 2.55" or 65mm
Tube OD 1.688" (probably like a 43mm spec tubing)

The ITR JDM, Toda and Spoon headers have a 65mm (2.55") OD collector, not 63.5mm. The Toda has a double walled collector but not like the ITR JDM which has the anti reversion chamber so there is a gap between the inner and outer tubes. The Toda header's inner tubing is in contact with the outer tubing so it's effective ID is greater than the ITR JDM header. The DC JDM 4-1 has a 2-1/2" OD collector and is probably 16g material so it's ID is 2.370".

The Mugen is a 60mm OD system however I've read the muffler necks down to 2-1/4" OD tubing, or maybe somebody measured the ID of the muffler and got 2-1/4" and this is where this info started. I don't know what Mugen uses in their muffler, but 60mm OD tubing will measure very close to 2-1/4" ID.

60mm systems do fairly well on the car however US spec cats are 2-1/2" ID and when you bolt up a 60mm (2.36") OD/2.25" ID system to a cat with an ID of 2-1/2" you have a 1/8" wide lip all the way around the B pipe joint/flange which will cause turbulence.

SMSP-Who wishes a moderator would archive this information

 

Wow, that's indeed a lot of numbers. Thanks.
What I want to say is that the DC JDM has a bottleneck in the collector near the O2 bung/connection. It's 60 mm OD there. I expected it to be 63.5 mm OD. You agree with this?

 

I haven't seen a DC JDM so I'll take your word on that. But, I can confirm the 2-1/2" measurement at the donut area since that is what DC told me on the phone. BTW, I wouldn't classify reductions in tube size in the collector as a bottleneck.

 

I can confirm that with my accurate measure of my recently received JDM DC 4-1


The following are taken at the collector at the very donut end of the header. I don't care about the size of any other section:
OD = 64mm
ID = 61mm
I notice my collector is not a PERFECT circle and that's why the measurement is not exactly 2.5inch.

SMSP, did you received my email about the cat order? Can you just send me an mailing address so i can send you my payment? IM is fine too. Thanks for taking the time.

Henry

 

I just did a search on this email adress henrycheang@hotmail.com and didn't find anything, so I guess I didn't get one. I had one customer who couldn't get the 2-1/2" donut on his DC JDM, I suspect it was due to an oval collector tube.

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