New Header, New Midpipe

Ever since putting in the VVT motor, my header situation has been sub-optimal. It was a Jackson Racing header (with the EGR fitting removed) which was better than stock, but it had a good bit of weld on the inside of the primaries directly in front of the ports. That big ridge is not great for flow:


I managed to work a deal on a Maxim Works (Mazdaspeed branded) NB header from JDM Land. Check out how clean the transitions from the flange to the primaries are:


After cleaning up a bit of surface scale with the wire wheel, it dropped right in. The JR basically had to be wrestled out. One more reason I like the Maxim Works better. And for what they cost new, it should be better.


Unfortunately, but also kind of fortunately, the flange and gasket type on the Maxim Works is completely different (round vs donut on the Jackson Racing), so a new cat-delete pipe had to be whipped up.

You’ll note that this is the 3rd or 4th iteration of the cat delete pipe, depending on how you’re counting. So while I dreaded the job a bit, I was also looking forward to doing it right. The exhaust hung a lot better with the last version than it did with the first version (not that it was a particularly high bar to meet…), but it still scraped the cat-back portion at the top of my hill coming out of the shop, so I wanted to make triple sure that there wasn’t something else amiss.

There was something else amiss. The cat-back is a slip-fit with the axle back, and is secured by a large band clamp. Works fine, but doesn’t lend itself to repeatable installation, apparently. Because it turns out that the last time the exhaust was out (who knows how long ago that was), when I reinstalled it, I clocked the cat-back incorrectly into the axle-back, and it was tweaked in a way that forced everything lower than necessary.

This photo, by way of comparison, is with the new mid-pipe tacked up and bolted in place, and is taken by a lower angle (showing more of the exhaust) just so you can see some of the exhaust towards the right hand side:


That is WAY better, and should pretty well cure the scraping issue once and for all.
It also appears that I AM capable of learning from my mistakes. Instead of the pie-cut and poorly fit nonsense from before, I got it in 2 sections (with a small mandrel bend on each end, slip-fit flanges, and flared 1 of the tubes just enough that the 2 pieces were nearly a slip fit. That allowed for a bit more flexibility in fit up, and a much stronger weld (lap weld vs butt weld). And because occasionally the kids let us sleep these days, I managed to put the flare on the downstream side so it would flow more smoothly (ie: into the flare) instead of tripping over the hard edge of the downstream tube if it were flowing out of the flare.


The slip fit flanges allowed a ton of freedom when fitting everything up, to the point that both flanges had maybe 1/16″ of tubing sticking out past the flange to get the correct angles. A flap disk trued everything up nicely.


And finally, after a final test fit and a bit of grinding to clean up some booger-welds where I had to clean up after blowing through the tubing, a coat of high-heat paint to keep everything shiny.



2 thoughts on “New Header, New Midpipe

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