Returning to my exhaustive threads, l have managed to find a spare set of header pipes to continue my experiments thanks to brother in Buells.
If you recall, l had developed a Venturi shaped insert to fit between my XB9s header collector and the muffler to enhance exhaust gas flow. I first discovered this phenomenon when l shaped some metal filler into the neck of my Stealth muffler to smooth steps in the flow. I had formed a sort of flare or bell shaped entry to that muffler which resulted in a dramatic improvement in throttle response and associated sound!
When my ears started to give me gip, Andy on the recommendation of pash, l fitted a standard XB12 muffler. This gave a quieter exhaust combined with better top end rush, but a noticeably muted bottom end torque. Combining ideas from my stealth experiments lmhit on the idea of making a metal sleeve Venturi to enhance things. After 3 tries l arrived at the current Venturi shape. This seems to have brought the midrange torque rush down range by about 700 rpm.
In my previous threads l hinted at some directional stability issues during an overtake. I had put this down to my bad riding, but repeat scenarios have shown that this was a real effect. Late last year on a bright high barometric pressure day when pulled out to overtake some cars and apples a big handful of throttle on a slight incline, the bike crabbed towards the opposite verge. I had to roll off the throttle and straighten up parallel to the nearest car before l could open up again to complete the pass.
Yes l know that if you tried the same thing on a 12, it would just lift the front while cranked over, and you would have to shut off slightly. No my 9 will not quite wheelie on the throttle alone at that speed.
Still there is a strong surge at rpm that was not there without my Venturi.
My plan with the spare header was to have the Y collector cut off and one of improved shape cut and welded in place. I know that Albert does a complete header for my bike, but that features bigger bore header pipes. That would factor in another element to the design and would not confirm my suspicions about the standard collector. I want to preserve low end stomp over top end power anyway.
My contention is that if the Y shaped tin that the two standard header pipes are welded into was better contoured with a seamless join to the incoming pipes that a whole better responding XB9 can be had.
Ironically my spare header looks better inside the internal plumbing of my original header. The step from the incoming twin pipes where they are welded into the collector looks more flush. So there could have been some minor inconsistency in production? Now l am in a quandary about whether or not to cut up the better header or just fit it?
Having another good look inside today, l can see that the factory that made the pipes did stamp or press the sides of the Y collector inwards to form a slightly pinched contour that mirrors the twin entry pipes. However this ‘pinch’ point does not look consistent in shape as it goes in, out, in, then out again to flow into the single large pipe exit. Instead of going to the hassle of fabricating a new Y collector l can see a way of improving the shape of the existing metal. By applying heat and using a cold chisel, l think that the sides of the pinch point could be beaten inwards by 2 to 3 mm over a length of 30 or 40 mm to create a more pronounced ‘valley’ flowing towards the Siamesed pipe. This would reduced the volume of the collector and reduce the chance of gases ‘stalling’ or slowing at this point.
If successful l could then run this tweaked header with and without my Venturi to see how effective the pinched collector is.
Shame about the lockdown, but then it could be a while before l get around to actually swapping pipes on my bike. More measuring to do first with my micrometer!