People that have measured the jdm collector shows that its 2.38" not a true 2.5". So why does everyone say its 2.5"?

 

2.5" (or 65mm for JDM) is the OD, not the ID. Everything exhaust related is measured on the OD with the exception of universal cats because they are made for flanges (measured on OD) to fit inside of them.

 

2.5" = 63.5 mm
JDM collector = 65 mm OD but there is an inner tube inside it.

 

I got that inner tube removed... but gained nothing. Oh well.

 

Does the inner tube make it quieter... if so is it quieter than the DC JDM 4-1 header??? TIA

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by DutchITR1689 &raquo;</TD></TR><TR><TD CLASS="quote">2.5" = 63.5 mm
JDM collector = 65 mm OD but there is an inner tube inside it.</TD></TR></TABLE>

I dont think this is correct...the OD of the header is 60.5mm (2.38") I think the reason they call it a 2.5" collector is because 2.38 is a bit of a mouthfull and its simpler to call it 2.5 to imply that its the bigger JDM sized collector. Mugen/Spoon/HKS/5Zigen/Apexi/Toda/Feels/Vision JDM headers all have an OD of 60.5mm (2.38) the inner diameter is nearer 55m (2.2") i think.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by mugenracer &raquo;</TD></TR><TR><TD CLASS="quote">
I think the reason they call it a 2.5" collector is because 2.38 is a bit of a mouthfull and its simpler to call it 2.5 to imply that its the bigger JDM sized collector. </TD></TR></TABLE>

So kind of like a 2x4? Even though its not really 2 or 4".

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by KOALA YUMMIES &raquo;</TD></TR><TR><TD CLASS="quote">

So kind of like a 2x4? Even though its not really 2 or 4". </TD></TR></TABLE>

Huh?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Rguy &raquo;</TD></TR><TR><TD CLASS="quote">

Huh?

</TD></TR></TABLE>

you know, a 2x4 board of wood. It's actually 1.5" x 3.5", but its easier to say 2x4.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 743power &raquo;</TD></TR><TR><TD CLASS="quote">

you know, a 2x4 board of wood. It's actually 1.5" x 3.5", but its easier to say 2x4.</TD></TR></TABLE>

no....it is not because it is easier.....
it is industry standard....the wood does start out at a 2x4 but then is dried to the finished 1.5x3.5

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by chad &raquo;</TD></TR><TR><TD CLASS="quote">

no....it is not because it is easier.....
it is industry standard....the wood does start out at a 2x4 but then is dried to the finished 1.5x3.5</TD></TR></TABLE>

 

you learn something new everyday

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 743power &raquo;</TD></TR><TR><TD CLASS="quote">

you know, a 2x4 board of wood. It's actually 1.5" x 3.5", but its easier to say 2x4.</TD></TR></TABLE>

Thank you , I know he wanted to flame me.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by chad &raquo;</TD></TR><TR><TD CLASS="quote">

no....it is not because it is easier.....
it is industry standard....the wood does start out at a 2x4 but then is dried to the finished 1.5x3.5</TD></TR></TABLE>

heh, I should have know that. I watch this old house and the new yankee workshop like 4x a week.

 

Every header I've ever measured with a "JDM collector" ends up having an inside diameter of around 2 1/4 inches give or take just a tad. As mentioned before, industry standard.

 

According to the Takakaira site the HKS B18C header has a 65mm collector which is 2.559" (to be exact) so its either a mistake and its 60.5mm like all the rest or it is the only true 2.5" collector out there.