Hey all,

I was just reading an old Hybrid page article about the JDM 4-1 header. It lists that the ID of the collector is 2.25 " while stock USDM is 1.75 ".

Are off the shelf (DC, Comptech, etc.) USDM headers all 1.75 ID at the collector?

People recommend the JDM (Spoon, Toda, etc.) or custom (SMS, HiTech) headers since they have 2.5" collectors. Do these all have 2.5" ID or OD at the collector? Or are they 2.25 ID like the JDM 4-1.

My recent dyno I made 177.6 HP and 119 TQ with my Toda Bs, compression, PnP, etc. My A/F ratio was 15-16 during this run! DOH! Anyway, I've richened it up so that should get me a few ponies back (SOTP estimate at 180 HP and 120 TQ), but still short of where I want to be.

The missing link (besides cam gear tuning) for me is my header, cat, and exhaust (curently Neuspeed 4-2-1, RT Cat, and Greddy Exhaust).

I'm hoping for an SMS next year, but just curious how the various contendors compare in terms of specs that affect perf.

Well, what specs do affect perf: primary tubing ID, collector ID, also the lengths of the various pipes...

Any input or thoughts are appreciated.

Thanks,

FB

 

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Well, what specs do affect perf: primary tubing ID, collector ID, also the lengths of the various pipes...
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You'll be hard pressed to find a manufacturer that will tell you all those figures! Everyone of those things affects the performance of the header.

 

Not to be an *** or anything, but all of the Japanese headers should be in metric dimensions- so they will be more than 2" but less than 2.5". 60mm if memory serves. The SMS and Hytech will be in inches and thus have slightly bigger bore.

1 inch = 25 mm (approx)