Dunstall-type 2 into 1 into 2 exhaust

I almost bought a set of these back in '06 but decided I didn't want to get rid of the center stand. Now I'm thinking about it again. The one I almost bought was a NOS off Ebay but I don't see any now. Anybody here know if they are being made anywhere?

Look at http://www.vikingexhaust.com/getPart.asp-id=85.htm.

MexicoMike said:

I almost bought a set of these back in '06 but decided I didn't want to get rid of the center stand. Now I'm thinking about it again. The one I almost bought was a NOS off Ebay but I don't see any now. Anybody here know if they are being made anywhere?

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Why do you want one?

Aesthetics? Well someone might like the look!

Performance? Doesn't fit in with most theory or practice!

It may have more ground clearance?

Just because it is Dunstall?

Just because it is different?


I had one in the '70s and used it once, because I had nothing else to fit the head that I also used once! I only used the front section with a link pipe to a UK speedway silencer, so it was used as an oddball 2 into 1 really.

It did the job surprisingly well. But the silencer was very heavy, and in truth I hated the aesthetics.

I bought one in the late 70s for my 850 commando with combat cam. I liked the look and the sound but the Dunstall Decibel Silencers turned into decibel enhancers after a few weeks. It felt faster but might have just been the effect of spending money . Ground clearance over curbs in bumps was much reduced . I also bought a compatible centre stand which I still have but found it was easy to bend .

I thought these were designed in conjunction with Dr Gordon Blair? If so I would have thought they were very much supported by theory. Is this right, or have I got my history muddled up?

Fast Eddie said:

I thought these were designed in conjunction with Dr Gordon Blair? If so I would have thought they were very much supported by theory. Is this right, or have I got my history muddled up?

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I can clearly remember the statement by Dunstall that these 2 into 1 systems gave some increase in performance, and were designed by dr Blair at Queens University Belfast.

Peter R said:

Fast Eddie said:

I thought these were designed in conjunction with Dr Gordon Blair? If so I would have thought they were very much supported by theory. Is this right, or have I got my history muddled up?

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I can clearly remember the statement by Dunstall that these 2 into 1 systems gave some increase in performance, and were designed by dr Blair at Queens University Belfast.

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Has to be said that Dunstall didn't sell anything with a statement that it reduced performance!

Note: 'most theory or practice' No body else did it. And Dr Gordon Blair wasn't 'most' theorists. I can't be sure either, but I thought his contribution was more to the long taper megaphone that was the Decibel silencer! He was certainly responsible for long slow taper megaphones used on some Seeley G50s.

As for ground clearance over curbs, understood, it being low slung in the centreline, but in less mundane riding it should have fixed the touching down in left hand bends of the header pipe that was always a pain on my Fastback! Norton 'production racers' at one time solved that by running the left pipe under the right, for a right exit, and moving the engine over in the frame! Later for PR bikes they simply tucked the pipes up/in more.

I had one on my Commando back in the day and it definitely felt like the bike had more mid range urge, and my friends said how good it sounded when you gave it some welly. The downside was that the pipe came unwelded from the stub secured by the exhaust rose. This happened twice and I gave up and went back to peashooters and ordinary pipes.

If memory serves correctly, Dr. Blair designed the 2-1-2 and a student of his (unnamed) along with Dunstall designed the silencers (Decibels). However, I find that memory doesn't always serve correctly .
Lance

I've got a Dunstall Catalog from 1971.

On the 2-1-2 exhaust these is a claim from an independent journalist that 1.15 seconds was knocked off the standing start 1/4 mile time just by installing the system.


When I got my '72 750 in '76, it had one on it. Can't say I was impressed with it. Seemed like shoddy construction, weak brackets, mufflers fell off several times.
i ended up using stock headers and the dunstall mufflers.

Installed a full set on a 73 Mk1 back in about 74.
Definitely had more mid and top end, idled and ran smoother.
Think I bumped the main to 280, maybe 270.
Seems to lose a little on the bottom.
Definitely ran out harder.
Couldn't keep the center sections tight.
Always figured a welded center section would be better.
It appears Viking has done that.
Look no further than the current hi po Vtwims, Ducati
Aprila, RC 51's all run 2-1-2. Make no mistake, it works.

I eventually went back to stock head pipes and the Dunstall
Muffs. Ran better, smoother than the original Pea Shooters.
Just didn't look as nice.

MichaelB said:

................
Look no further than the current hi po Vtwims, Ducati
Aprila, RC 51's all run 2-1-2. Make no mistake, it works.

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I didn't actually say that 2 into 1, or 2 into 1 into 2 didn't work.

What always struck me as strange was the very short primary pipes ending in a welded Y piece of the same diameter. Remember I took an exhaust off the bike when I changed the head for this one event (due to a dropped valve!). That exhaust was made to works dimensioned primary pipe lengths, as is my current exhaust!. It happens I prefer separate pipes, but I did try 2 into 1 with the same primaries, pretty much gaining the opinion that the effectiveness of a 2 into 1 is based on the collector design. The Dunstall system does not seem to have a well designed 'collector', but note I also said it was surprisingly effective for the one event.

BTW, I might dispute the RC51, deleted from the Honda catalogue in 2006, as being 'current' :wink:

I would also suggest that V twin exhaust design is a completely different topic to 360 degree parallel twin exhaust design!

You cannot equate the effects of the exhaust design on each engine when the exhaust pulses hit the collector at such different times.

Note that those who have fitted 90 degree (or 270 degree!) cranks to Nortons run separate pipes, not the ubiquitous Steve Maney 2 into 1 design! (which has full length primaries with an excellent collector design!) Simply because the 2 into 1 does not work on these engines!

Well FWIW I too only remember this system being called "Dr. Blair 2-1-2". Doesn´t make it a fact though....
Tommy

I have an original Dunstall 2 into one into 2 on my 72. Fitted with the often seen Emgo Dunstall replica silencers, fiberglass packing removed. I've read many road tests and reviews from period magazines about this system. With my setup, I would say it's quieter than another 72 with peashooters. (my son's bike, ridden side by side). In several original road tests, I've seen the testers mention how loud the 72 stockers are. One (Big Bike IIRC) referred to the throttle as the "loud handle" or something like that. We may disagree of course, but the general consensus on many of these tests were that the original peashooters were loud for their day. On some of the Dunstall tests, I've seen several comments by testers that seem to imply that you could get a similar level of performance to the stockers but less noise by using the Dunstall setup. Not more power, but similar to stock with less noise. No real evidence, and I know road tests from that period could be highly opinionated without many hard facts to back things up. I can't think of too many exhausts that I've seen advertised that way. Most any aftermarket ads tell you that more power will be the result, and the Dunstall adverts I've seen say more power. I would say on my setup, with the Dunstall 810 kit, performance is good with a very strong pull once it gets above 3,500 rpm. Nice sound to it, can't really put a finger on what it sounds like, but different than pea shooters.

The system used on the 750SFC Laverda which has the cross under the motor, seems to work. If you are getting the most out of a Maney 2 into 1, it is probably too loud.

The claimed increase was in the mid rev range, very difficult to measure without access to a dyno;
"In the search for a more efficient exhaust system without additional noise, Dunstall worked closely with Dr Gordon Blair of Queens University Belfast, Ireland. The exhaust pipe design (two-into-one-back-into-two) was entirely Dr Blair's while one of Dr Blair's students, Sam Coates, and Paul Dunstall helped to work out the silencer design and dimensions. "


http://www.woodgate.org/dunstall/history.html

SteveA said:

What always struck me as strange was the very short primary pipes ending in a welded Y piece of the same diameter.

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But Steve, you've got to remember the exhaust pulses are alternating left/right. There is not a continuous gas stream from each cylinder. So maybe there is method in the madness?
Cheers
Rob

In about 2011, I asked Paul Bryant (Viking exhausts) to built a Dunstall 2-1-2, but with a few subtle differences.
I asked for the down pipes to tuck in more closely to the down tubes and for the single pipe underneath to run fairly close to the crossover frame tube. Also I asked for the silencers which were in this case peashooters made by Paul, to run from a higher start point than the standard Dunstall and to more or less follow the standard Commando silencer lines/angles.

The pipes definitely changes the power characteristics a bit.
1. Tick-over was very quiet. (Not a power characteristic...I know).
2. At low revs there was a bit less torque.
3. At (IIRC) about 3,500 / 4,000 rpm the exhaust note changed and the bike pulled noticeably much stronger from there to 7,000 rpm and felt as if it wanted to keep revving which had not previously been the case, but I had to show self restraint and change gear.

As I said, this is using Peashooters which were 1"5/8 diameter, the exhaust tubing enlarging 1/8" at each of the Y junctions, and starting from 1" 3/8 on the down pipes.

Reggie said:

In about 2011, I asked Paul Bryant (Viking exhausts) to built a Dunstall 2-1-2, but with a few subtle differences.
I asked for the down pipes to tuck in more closely to the down tubes and for the single pipe underneath to run fairly close to the crossover frame tube. Also I asked for the silencers which were in this case peashooters made by Paul, to run from a higher start point than the standard Dunstall and to more or less follow the standard Commando silencer lines/angles.

The pipes definitely changes the power characteristics a bit.
1. Tick-over was very quiet. (Not a power characteristic...I know).
2. At low revs there was a bit less torque.
3. At (IIRC) about 3,500 / 4,000 rpm the exhaust note changed and the bike pulled noticeably much stronger from there to 7,000 rpm and felt as if it wanted to keep revving which had not previously been the case, but I had to show self restraint and change gear.

As I said, this is using Peashooters which were 1"5/8 diameter, the exhaust tubing enlarging 1/8" at each of the Y junctions, and starting from 1" 3/8 on the down pipes.

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Martin, do you still use this pipe, I think I recall that you reverted to stock pipes?

I'd very much like to test your system on my next dyno day, would you be prepared to send them to me? All in the interest of Norton science...!

robs ss said:

SteveA said:

What always struck me as strange was the very short primary pipes ending in a welded Y piece of the same diameter.

Click to expand...

But Steve, you've got to remember the exhaust pulses are alternating left/right. There is not a continuous gas stream from each cylinder. So maybe there is method in the madness?
Cheers
Rob

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If the tail pipe of a 2 into 1 is smaller in cross-sectional area than the two pipes entering it, you go backwards - you lose too much top end. If the tail pipe is big enough the pipe is usually too loud.