A 1975 GT-750, aka Water Buffalo at a local shop, not the desirable '72 model with 4 shoe brake, looking neglected and plundered, but not past saving, despite the missing sprockets and chain, engine case, calipers and more. Someone has drilled the discs in an effort to get some wet weather stopping ability, braking still featured a split second of panic but after that, whew, it did work... There seems to be an exhaust pipe still in place, though the mass of mufflers usually present isn't there, maybe it has a 3-1?
thanks, Drew
I am pitiably ignorant concerning expansion chamber theory & practice. I've seen those 3:1 chambers and have wondered: Are they purely cosmetic, or is it possible to tune one chamber to serve three cylinders/pulses?
ReplyDeleteYou're not alone. Because they were never used on race bikes and because any (limited) info I've seen back in the day said "midrange is enhanced at the expense of top end" I would say, it's just a stylish (beauty in the eye and all that?) muffler with a fair amount of weight saving (especially on a Buffalo). But guessing; expansion chambers work because the sound wave resonates back to close off the exhaust port artificially at a certain rpm range, the exhaust port is open for roughly half of the stroke (180°) and the tail end of that opening would be when the sound wave would close it off. The triple fires every 120°, so I would say the returning sound wave from #1 would meet the exiting sound wave from #2 part way along the pipe and then #3 would join in and then everything in that pipe would be confused for ever more.
ReplyDeleteDoes this mean that it might work on a twin? I really don't know. We need someone who did their thesis on two stroke pipes to chime in.
As long as that person is cogitating anyway: I read that it's potentially possible to baffle/muffle an expansion chamber enough to make it very quiet, without losing performance.* :Ahem: uh, person, could you have a go at confirming/denying please?
ReplyDelete* The mandate to make it quiet would dictate how the pipe is dimensioned. I didn't mean one could stick a big old muffler on the end of a pipe not designed for it.
I think this topic showed up earlier on this site, and trying to work out the waves and such made my head hurt. So I'll offer a definite probably not...
ReplyDeleteRe noise: Gordon Jennings, in the 2 Stroke Tuner's Handbook, accidentally found out that shoving the stinger right down into the fat bit of the chamber reduced the noise. The idea, from memory, was that the stinger wasn't at the point of max pressure in the reverse cone. The stinger is really just a bleed for the exhaust, and serves to maintain enough pressure in the chamber for all the sonic stuff to happen. ISTR seeing kart chambers with the stinger off the side of the main body.
Of course, if there's no stinger, then there's an opportunity for an extra muffler type thing (low restriction!) just to keep the neighbours even happier.
Drat!!! Now I've got to go and reread Jennings. The things you people make me do...
rdguy
Ack!!
ReplyDelete"Of course, if there's no stinger..."
Of course there's a stinger. A more careful writer would have said "if there's no *external* stinger..."
[Resumes reading Jennings]
https://www.cyclenews.com/2020/06/article/archives-column-1972-suzuki-gt750-water-buffalo/
ReplyDeleteThank you for the link! I've seen some grainy bad angle pictures of GT750 flat trackers but never heard this story. I have collected some pictures of T500-based flat trackers, they will be a post one of these days...
ReplyDelete