The Bucket Foundry

[husaberg]

On the presumptuous presumption that you're talking about me, no worries: I hit the sack far after midnight.
And on the subject of silencers: I did try the Roe annular discharge silencer but I was not entirely satisfied with the results.
I also tried Flettner's plan of an exit at the pipe belly (which I used to call a stoma when there was no-one around).
Back then I drove a Kawa H2 (for you youngsters: a 750 cc two-stroke triple) with a couple of mods, like 3 38 mm Mikunis and a homebrewn exhaust system, consisting of three conventional expansion chambers, but without the tailpipes. Instead they had exits at their bellies that came together in a big pot 120 mm Ø x 300 mm length under the engine, in front of the rear tire. They still made me ride at the rear of the group when we went on our sunday tours, but it was a little quieter than three stingers with absorbtion dampers.

I was more hoping for the why explanation to the buried stinger or the mid exit being quieter.


ps I heard Heisenberg went for a drive in Munich and got stopped by a traffic cop. The cop asked, "Do you know how fast you were going?" Heisenberg replied, "No, but I know where I am."

[Frits Overmars]

I was more hoping for the why explanation to the buried stinger or the mid exit being quieter.

As Gordon Jennings wrote:

the chambers' outlet to atmosphere was taken from a point where the pulse was at its lowest amplitude - rather than from the high-pressure area at the tip of the baffle-cone.

I heard Heisenberg went for a drive in Munich and got stopped by a traffic cop.
The cop asked, "Do you know how fast you were going?" Heisenberg replied, "No, but I know where I am."

Do you happen to know if Heisenberg was driving his new car?

[Grumph]

I too played around with annular discharge silencers in the late 80's. I'd got tired of losing packing material...

My empirical conclusions were that they were fine for 4T's but 2T's not so much.
I'd assumed that the 4T's lower frequency pulses suited this system better.
It may however have simply been a too large annular gap. Can't be bothered retrying now.

[husaberg]

As Gordon Jennings wrote
o you happen to know if Heisenberg was driving his new car?

Chairs for the explanation re jennings
I heard Heisenberg actually got off the ticket as he said to the policeman he was in a rush taking Schrodinger’s cat to the vet, it turned out the cat was so sick the vet couldn't work out if it was dead or not.

Husaaaa!! ......... didn't you know? - Tulips just won't grow behind dykes, that'll be why!

I heard that was why van Gough cut of his ear...

[Frits Overmars]

I heard that was why van Gough cut of his ear...

Don't let the facts spoil a good story...
Van Gogh didn't cut off his ear, he 'merely' cut off one ear lobe. Not because of tulips or dykes, but because he had mental problems all his life.
I somehow get the impression we're a bit off-topic...

[WilDun]

Yes let's keep international relations on an even keel (within reason) - I am guilty of getting really off course (of course)!
So to that end, I have decided to delete a couple of my even more pathetic contributions!

Getting back to the exhaust with the closed end and side discharge stinger - why did this not become generally accepted practice earlier?
As for those people who did find that it worked ok, including Speedpro, with his similar adjustable internal stinger - what made you guys revert to the conventional layout again?

[Frits Overmars]

Getting back to the exhaust with the closed end and side discharge stinger - - - what made you guys revert to the conventional layout again?

Simplicity. If you don't work on slow-revving engines, you won't have to accommodate long pipes and then the silencer behind the end cone is the simplest solution.

[WilDun]

Simplicity. If you don't work on slow-revving engines, you won't have to accommodate long pipes and then the silencer behind the end cone is the simplest solution.

Does there come a point where there might be the possibility in the world of everyday two stroke workhorses (probably none left on the roads anymore) of having a relatively "tame" engine with a wide torque spread with good fuel consumption figures - would it then become feasable to have a parallel pipe (or something close)?
Probably I'm wrong of course, but all this harmonic stuff seems to add a lot of (unseen) complication and if it works really well, it only works well in one area of the rev band, not particularly good on the streets or highway in the hands of a lunatic who is fond of wheelies!
Of course, in competition it is necessary if a tenth of a horsepower increase means a lot to you! (see ESE).

[Flettner]

trouble is a twostroke without a chamber is a lawnmower.
The chamber makes sooòoo much difference.

[Frits Overmars]

Does there come a point where there might be the possibility in the world of everyday two stroke workhorses of having a relatively "tame" engine with a wide torque spread with good fuel consumption figures - would it then become feasable to have a parallel pipe (or something close)? .. All this harmonic stuff seems to add a lot of (unseen) complication and if it works really well, it only works well in one area of the rev band, not particularly good on the streets

We passed that point a long time ago Will: the two-stroke workhorses of the 1960s with four speeds, enclosed chains that had eternal life compared to what we have to put up with now, and silencers that didn't yet double as resonant chambers. But as Flettner says: "The chamber makes sooòoo much difference".
On the Aprilia racers the pipes tripled the power. If you want to get rid of that pipe, you'd have to triple the cylinder capacity. Worth a thought...

You're right about "this harmonic stuff" only working well in one area of the rev band. Six-speed street bikes can be fun for a while, but I can assure you that twelve speeds are no fun at all. For everyday use I prefer a bike that doesn't need a downshift each time I want to overtake someone. I'd rather have a CVT, or an E-bike, once we get batteries with half the weight and five times the capacity. I can do without the noise, although I think the absence of noise will eventually kill the public interest in motor sports.

[Michael Moore]

I've long thought that a 650-700cc 2T twin with tuning and flywheel mass like my 325cc Bultaco Sherpa T would make a pleasant street engine. The exhaust system on the Bultaco is straight pipe and mufflers. I suppose the closest thing to that would be the Silk version of the Scott.

I've got something like that with my 670 Honda 4T parallel twin which makes a massive 45 or so hp. I like the DCT transmission too, not shifting/clutching is fine with me, but I can always punch a button to change a gear if I feel a need for that.

cheers,
Michael

[WilDun]

Well, I guess that in Neil's Gyro, a chamber is an asset because of it's engine revs staying inside the powerband most of the time, same for fixed wing aircraft
.
Trouble is, that whatever we say to the contrary, tuned pipes more or less equate to a turbo! (did I really dare say that?).
A turbo (or supercharger) in everyday street use is acceptable, however our thinking unfortunately seems to be always driven by racing rules and this is actually taking the two stroke off our roads.

If I possibly have broached this somewhere before - forgive me, but if some built in (integral) mild forced charging could be introduced and combined with milder exhaust porting without being affected by the need for the (finicky) resonance thing, to address the charging problems and help keep the fresh charge completely out of the exhaust system.

If we wanted to keep the "sound" going, we could use the two stroke (suitably tuned) driving a generator in a Hybrid! - maybe that would be a bit of a travesty, ie losing all those beautiful (and costly) gearboxes!

And yes Michael. I had meant to say, take a look at trials bikes!

[Vannik]

I've long thought that a 650-700cc 2T twin with tuning and flywheel mass like my 325cc Bultaco Sherpa T would make a pleasant street engine. The exhaust system on the Bultaco is straight pipe and mufflers. I suppose the closest thing to that would be the Silk version of the Scott.

I've got something like that with my 670 Honda 4T parallel twin which makes a massive 45 or so hp. I like the DCT transmission too, not shifting/clutching is fine with me, but I can always punch a button to change a gear if I feel a need for that.

cheers,
Michael

Then you should use a tripple with a log manifold, it stays mostly in tune through the rev range if the blowdown pulse for one cylinder is used as the plugging pulse for the previous cylinder. This only works for 3 cylinder engines and is why outboards prefer I3 or V6 layouts.

[WilDun]

Have often heard that - good suggestion of course ..... but does it keep the fresh charge out of the exhaust? - still a resonance problem??
Mixing of the fresh charge with the exhaust gases is the main problem and I feel it has all but killed the two stroke! If this didn't happen surely the oil would be burnt completely and there would be no smoke but when a two stroke starts up from cold, there is always oil in the exhaust which almost disappears when everything heats up, and of course there is the unburnt raw petrol as well! - second only to the Wankel!! - Sorry Frits.

[EssexNick]

Would there be any difference in stinger nozzle size, between a straight pipe and one that exits mid chamber?