I swapped out my stock 1994 Si-VTEC header for a DC JDM 4-1 header a few weeks back. Even though everyone refers to JDM headers as having a 2.5" collector, it is in effect only 2.38"(60.5mm) Before buying the DC 4-1 i jacked up my car and measured the OD of my stock collector and found it to be 60.5mm (2.38") and so thought that the DC header should bolt straight up to my cat without modification. When we got my header off, i noticed the gasket (donut) to be a lot smaller than the DC donut and measured the stock one as 2.25" We managed to make the DC donut seal into the 2.25" cat inlet and bolted everything back up again. (although i had a look under today and i think its starting to blow out slightly ) Then tonight when i was looking at the stock header i discovered that even though the OD of the collector is 2.38" the ID is only 1.75"!!!! There is an internal pipe within the collector end reducing the ID to 1.75"...why the hell would they do that, isnt that more restrictive than even the USDM GSR collector?? No wonder i felt a huge difference when i drove the car for the first time with the DC JDM 4-1!!! The stock cat has a 2.25" inlet and i have a mugen 2.38" system from the cat back, that damn collector was strangling my engines breathing for the last year and i never realised Why would they have a 60.5mm OD collector but only have an ID of 1.75"...doesnt make any sense in my book!

red line is 2.25"
yellow line is 1.75"

 

heres another pic for reference

itr 4-1

 

is that a JDM ITR 4-1?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by mugenracer &raquo;</TD></TR><TR><TD CLASS="quote">is that a JDM ITR 4-1?</TD></TR></TABLE>
Dude you need to read his post. He says it's a JDM DC 4-1.

Congrats on finally getting a header. Now becarefull not to dent it!

 

B2finity, i was asking Silver was the picture he posted a JDM ITR 4-1 or what? He said it was an ITR 4-1, he did not mention DC.

And i've put a small dent in it already, going over a ramp into my mechanics shop!

 

its a OEM JDM ITR 4-1

i dont think i need to worry about denting it

this header has been sitting in my room for over 2 months! hopefully if UPS comes through, ill be installing it this weekend(carsound cat comes on friday)

 

i'm very curious where you got that dent shield from. Im interesting in getting one- how much, where, etc. ?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by TIroneous &raquo;</TD></TR><TR><TD CLASS="quote">i'm very curious where you got that dent shield from. Im interesting in getting one- how much, where, etc. ?</TD></TR></TABLE>

try doing a search under "skid plate"

 

http://www.heeltoeauto.com

 

thanks for all the info. I need to get a header.

 

hey , how or where wouldi get a skid plate for a dc sports 4 - 2- 1 header , it says on heeltoeauto.com that it should be used on 4-1 only or somthing like that , i just wanna know if that one will fit , or if there is one out there for me , thanks

JAY

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by jason bouchard &raquo;</TD></TR><TR><TD CLASS="quote">hey , how or where wouldi get a skid plate for a dc sports 4 - 2- 1 header , it says on heeltoeauto.com that it should be used on 4-1 only or somthing like that , i just wanna know if that one will fit , or if there is one out there for me , thanks

JAY </TD></TR></TABLE>
there are no skid plates for the DC, the one pictured only works on the OEM HONDA JDM ITR 4-1

 

damn , i guess i can weld a custom . .. . ..

 

The USDM GS-R header is also double-walled like the pic in the first post above. That's the reason why many people have that notorious rattle at 3K rpm, because the inner wall likes to rust and separate itself in certain places, then rattle against the outer wall.