I have worked through the initial issues in adapting the aftermarket Astro expansion chamber to Bultakenstein. The headpipe and main body, originally designed to be held together with springs, had been welded together at some point. I cut them apart and hacked off the gobby weld joint. I also cut off the unusable rear mounting tab and ground the reinforced base smooth. I’m currently fabricating a replacement from 2-inch OD steel tube. I mocked up an arrangement I’m happy with, at least as far as the physical configuration. I still think the volume and shape of the pipe won’t suit the stock Frontera porting, or be pleasant on the street, but at this point I just want to get it running. The new section I’m adding is slightly longer overall. I needed that extra bit of length to clear the frame downtubes, and this should also—in theory at least—move the powerband a bit lower in the rev range. That sounds like a good thing, but it might not be, because the dimensions of this pipe suggest it will come on the pipe pretty suddenly. At this point, I’m tweaking the length and angle of the new piece to ensure the pipe ends up exactly where I want it. I will then fabricate a new pipe hanger, tack everything place, and take it to my neighborhood welding pro to finish.
