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Old 03-18-2018, 10:49 PM   #15
KillerBMotorsport
NASIOC Vendor
 
Member#: 198281
Join Date: Dec 2008
Chapter/Region: MAIC
Location: Virginia
Vehicle:
2005 WRX/STi
WRB of course

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Have you guys actually tested stepped headers on a turbo application? I would recommend it all day on an N/A car or motorcycle with some decent rev capabilities. On a pressurized manifold you're going to see small gains over a small RPM range, and losses elsewhere. Unless you're making M-A-N-Y sets of headers, or plan on running some simulations on a +$100K simulation program (Nastran, ansys, etc...), you're just throwing darts at a wall.

IMO you're going to benefit most by using a tried and true design and doing everything you can to optimize energy transport (sound, heat, pressure pulse, flow, etc...) from port-to-turbine.

If you're concerned with your port being 39mm and our primary being 38mm, that's a super easy one to solve. First, our primaries being welded on both sides are going to be pulled open to fill the flange hole clearance. In other words, they should be a wee bit over 38m. On top of that, we give all the ports a grind and blending finish that will also open them up a wee bit too. Just for argument sake, let's say they aren't. To make them go from 38mm ID to 39mm ID is removing less than .020" from the material thickness. That could be blended in, in such a subtle way, that you wouldn't even see or feel it. S-m-o-o-o-o-t-h.

It's arguable, that increasing the secondary from 2" ID to 2 1/8" ID would be a performance benefit.... BUT... only if you're going T4, not T3. T4 is more typically on landspeed cars making +1,100whp. Big primaries are going to make decent torque, but flat elsewhere. Companies calling the 'big tube' headers 'race' headers is more marketing ploy of bigger-is-better than performance enhancement IMO.

Why do I hold my ground on the above? While transitions, larger whichever tubes and so on may attribute to gains under a small targeted area of the rev range, the increased losses in the form of sound, heat, pressure pulse, flow, etc, as mentioned above detract from performance in all other areas of the curve.

Is our off the shelf Holy Header the end-all-be-all of EJ header design. Heck no! It has to conform to space and fitment constraints. The Low mount header is a pretty decent upgrade about that, and beyond that you are talking a tube chassis car with an open front end, kit car, aircraft or whatnot with a custom space allotment.

We might have a used header coming available soon. It's been on the car a while and I don't recall if it's a V2 or V3. If you wanted to make your own setup, it would give you a good starting point to hack-and-tack from.

Here's an example of one of the best setups I think we've ever done. This was many years ago, pre-cast collector, but did the job very well.

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