Today l could choose between making a cut down badass tail light housing from my spare, or start tweaking my spare XB9 header.
Looking again at the two headers l have and other factory 9 collectors from pictures on eBay, l was shocked to see how much variation there is in welding and shape on supposed to be identical spec headers.
Some are very neatly welded and have a pronounced V shaped valley on each side of the Y shaped moulding to blend in with the two incoming pipes, other examples have crude welds and hardly any valley to the sides.
Where l measured a cross section of 26.5cm2 on my spare header, the sides of the Collector were almost bulging outwards!
I estimate that the variation at this point can be as much as 18%, which is a lot in anyone’s book! Is this why every XB9 feels so different to ride?
As l have explained at length elsewhere this void in the Y of an XB12 would be much less significant as those incoming pipes are much bigger in section. The ratio of incoming to the space in the collector is significantly less than on a 9. So what are the gases likely to do under those conditions?
I was also surprised to see by comparison that the headers that came with my XB were actually beautifully welded and that the Y collector looks to be very well contoured. It’s just inside where the incoming pipes appear to have a big step at the weld point. In almost the opposite fashion, my spare header looks more streamlined inside where the incoming pipes are welded, but with badly shaped blending from twin to single pipe there after.
As above l measured the spare collector cross sections as 22, 23.9, 26.5, 20 and 14.7 cm2 over a length of transition of about 92mm. By correction of pressing or hammering in the side valleys of the collector the profile should be 22, 23.9, 21.8, 19.4 and 14.7 cm2. Note the big change in the middle.
If l could clean out the pipe innards with a long brush, l could try lead filler to the back of the weld then shaping with a long grinder or file! That might even make my Venturi redundant!