Wondering which header would be the best ......assuming stock ITR with only a CAI right now ....but potentially in the future a couple more bolt-ons would be added if I knew I could eek out a little power after the Header (ie: intake manifold + throttle body + mild cams)

Two versions of the same header are offered, both with the same size output which I believe is 2.5"

Option 1 Step-up Piping Sizes (OD)
42mm - 45mm - 51mm

Option 2 Step-up Piping Sizes (OD)
45mm - 50mm - 55mm

Thoughts?

Will

 

Is the car going to need to pass emissions? Inspection sites are supposed to do a visual inspection also. When they see "after market" exhausts, they look for "CARB" legal markings.

JDM cars use 2.5" collectors, have more flow, create 10 - 15 more HP.

USDM Integra cars use 2.25" and rarely can you find a "CARB" legal 2.5" header, for the US cars.

 

Emissions requirements are not a concern, the car resides in a location which currently only does an OBDII scan for emissions, and there is even talk of scrapping the emissions program in its entirety.

 

the smaller piping designs will be geared more towards mid range power and preserving low end torque, the larger size will promote more top end power. The design of the header plays a role as well , in addition to the piping size, but assuming the same header design for both then it depends on what power band you want - mid range or top end.

 

they are both Tri-Y 4-2-2-1 design, each with 2.5 output.

Ideally I'd want to emphasize the mid to high-end power (ie: "on cam")

WC

 

I would try to mimic the Toda header design which starts at 45mm, one of the better proven header designs out there, even in replica form. A 42 mm primary is more like a Mugen design which does not make as much top end power as the Toda design. I am being very general here not knowing what brand you are talking about, but that should give you a good starting point.

 

option 2. I did quite a bit of searching though old threads when I was looking for a header. 45mm primaries is the way to go. 2 1/2" exhaust as well.

 

the ITR header test had some great information in terms of header design and sizing.

 

I see you are in Ottawa, come Feb 1 no more etest for us in Ontario. For an ITR motor I have seen both toda replica or hytech small tube replica make great gains paired with either 2.5"-3" exhaust no cat and a tune.