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All these tuning details matter not one bit if the exhaust wont fit, and it clearly wouldn't. The primaries for #2 and #3 stick our farther than #1 and #4. At this point we weren't quite sure where the subframe would sit, but it was pretty damn clear it would occupy the same space as the center two primaries.
Our first idea was to cut off the collectors and use an extra set of #1 and #4 primaries, like this. It would have been nice if something clever like this worked, but no…
By the way, the small stainless pipes over each primary are the air injection system. It's pretty common to remove these, but I can't imagine why. The air injection system is a remarkably simple passive system with no air pump. Each of the pipes simply pulls its air supply through a reed valve. When there's an exhaust pulse, the valve closes. When the low-pressure reflected wave bounces back, the valve gets sucked open and a little bit of fresh air burps into the pipe. This fresh air provides the oxygen necessary for the catalyst to clean up any unburned hydrocarbons still in the exhaust. Without the oxygen, the catalyst can't do anything and all the puppies will die.
There's a small chance this system might rob a fraction of a horsepower by taking away some of the suction of that reflected wave that would otherwise help suck in a little extra air during valve overlap, but I doubt the impact is significant. Besides, I'd never be able to look a puppy in the eye again if I removed them.
With our low-buck hack-job ruled out by packaging, we stepped straight up to full-sex race fab. I can't honestly remember why we were suddenly in such a hurry, but we ended up taking the car to SPD in Rancho Cordova, Ca, (not far from Miatabusa World Headquarters where the adaptor was being fabbed), handing them a pile of green paper, and letting them go to town. In an amazing two days, they turned out this intricate, flawless custom race header. TWO DAYS!
The close confines of the firewall and the passenger's side frame rail made this around-the-front layout pretty much inevitable, but SPD's workmanship made it all OK. If we're going to have something this sexy looking under the hood, might as well run it all around the engine so everyone can see it. Imagine what a waste of awesomeness it would be to tuck this kind of thing under the engine!
With the number of nerds we had working on this project, you'd think there would be pages of math behind the header design. Sadly, there was not. Primary diameter stayed stock, since we were using the stock primary flanges, and primary length was effectively limited by our packaging. This is an equal-length design, so the calibration should probably be changed, but we were expecting to do some tuning anyway.
We did make sure the header packaging worked well for turbocharging. When we take that step, the most we'll have to do is slip on a new collector with a turbo flange and make a few brackets to hold the weight of the turbo.
The only thing the header didn't really get along with were the fuel feed and return lines, shown here capped with orange caps. Since the fuel rail is on the opposite side of the engine anyway, we were already resigned to re-routing them. This turns out to be quite simple while the engine is out. I simply grabbed the lines and re-bent them by hand until they popped up on the top of the transmission tunnel, then cut off the excess length. If you were wondering how the fuel pressure regulator ended up behind the engine in the last installment, now you know.
Again, if we're going to have a part that looks like this, it might as well be front and center on display! I can't even begin to imagine how you weld a bead like that, especially down in the butt crack between two tubes. That's why I type for a living…
1 comment
Hey,
Do you have any updates on the reliability of this? Thanks!