Dunstall Ex 2-1-2

when there was talk of viking remaking the system i tried to get them to make the 3 part front as a 2 piece and use 850 style collets to correct this issue but some don't want to listen to experience.

This is the underneath, inc centre stand, of the Dunstall Cdo in the basement at Barber.
Quite clever / neat I thought...

F.E, this exhaust system certainly looks good, although I have my doubts if the center stand will work in this forward mounted position.

One of the delights of the Commando was and, indeed still is, an easy roll on off ergonomic centre stand ,this looks like it would be a pig to use . And it was expensive at the time.

Re;”Dr Gordon Blair was not an 'expert' but Dr Gordon Blair. He also designed the Q.U.B Seeley engine and was a noted authority on exhaust systems. Had one on mine, yes the design was fine the build quality atrocious”

Dr Blair was a university designer, with access to Dynos to prove or disprove if a system worked, but he was NOT responsible for the quality control of the build once it passed the design on to Dunsall-who had them built to a price

from an earlier post on this subject;


https://www.accessnorton.com/NortonCommando/dunstall-silencers.16311/#post-236815

acotrel said:

We have a refugee here in Australia who used to work with Blair at QUB. In fact he was the guy who started historic racing in Australia. If there was ever any way of getting something wrong, he would find it - not Blair, but his idiot disciple.

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Well .. . . . of couse!!!! You appear to have NO IDEA on how university’s work, - the Dr. or professor delegates the work to students who studies this subject as part of their course or to get a degree, Dr Blair didn’t do ALL the work himself!

. . . . apparently not just university's !

sadly even in centres of higher learning and disciples like engineering there are individuals who squeak through because they passed the course material, but are totally inept when it comes to real life... the old joke, Hi! i'm an engineer and here to help comes to mind or was that Hi! i'm from the government...and here to help

we still say,
Those that can, do , those that can't, teach , and those that can't teach, consult...

i'm still debating how i'm going to deal with the 2-1-2 exhaust and main stand once the Dunstall is reassembled.
i have read a number of comments that the dunstall stand for the 2-1-2 was flimsy and tipsy. current the bike only has the side stand which is badly worn and floppy, i may end up making a race style stand which utilizes the original main stand bushings and race type slide under lift.

Bernhard said:

Re;”Dr Gordon Blair was not an 'expert' but Dr Gordon Blair. He also designed the Q.U.B Seeley engine and was a noted authority on exhaust systems. Had one on mine, yes the design was fine the build quality atrocious”

Dr Blair was a university designer, with access to Dynos to prove or disprove if a system worked, but he was NOT responsible for the quality control of the build once it passed the design on to Dunsall-who had them built to a price

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not sure which particular hair you are trying to split. Surely everyone knows that Dr Blair was only responsible for the design and Dunstall for the manufacture

Fast Eddie said:

This is the underneath, inc centre stand, of the Dunstall Cdo in the basement at Barber.
Quite clever / neat I thought...


View attachment 7596 View attachment 7598 View attachment 7599

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Looking at the pipe diameter beyond the collector - the motor would have no top-end. It needs to have the same cross-sectional area as the sum of the areas of the two header pipes or you lose too much.
When you talk about Paul Dunstall, you are talking 1960s. We did not know much about Commandos back then and most of us also knew almost nothing about two-strokes. If you have a look at what Kenny Cummins at NYC does these days, he is way ahead of where Paul Dunstall ever was. Dunstall just happened to be amongst the first to try and get Commandos going and turn a dollar doing it. What he did was OK, but Gus Kuhn achieved more success.

Geoff Lather said:

Does anyone know if the Dunstall 2-1-2 ex system really did work well or was it all just marketing B.S.?

Thanks Geoff

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This has been an interesting read.
The answer is Yes, it works.
I ran it on my 73 850 in the 70's. Bumped the main to a 270.
Lost a bit on the lower end but picked it up in the middle and ran harder on top, all the way to valve float....
I often wondered how they'd work with more cam and compression.

This system was designed to work with the 'Dunstall' mufflers.
The system was tuneable as you could expand the connections. This was mentioned in the instructions.
Mine worked better with everything lengthened.
However, this dropped the center pipe and made it more susceptible to speed bumps and steep drives leveling off at the top.

Too all the naysayers, look no further than the High Po Twins from Aprilia, Ducati, RC-51 etc. All run 2-1-2 systems.

But alas, the maintenance... Mine were always working loose, rattling, dragging on speed bumps etc...
A real pain for one's only rider. Can only the imagine the hurt that looped center side could cause.
Tried the Dunstall muffs on the stock pipes and what a revelation. Picked up the bottom end and ran out better on the top VS. the Pea Shooters.
Not as strong as the 2-1-2. Admittedly, the Pea shooters looked better, the Dunstall's outperformed.
This is how I ran it till I sold it, spring of 1978.....

MichaelB said:

Lost a bit on the lower end but picked it up in the middle and ran harder on top

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More or less what I found, although I had / have reverse cones on my system, but in 1 5/8" diameter.

With all this positivity about the dunstall 2 into 1 into 2 system I may be tempted to give it another go
I still have the down pipes somewhere but the rest of the system is gone
I'll remake the centre pipe etc and I have a pair of replica dunstall decibels but that could be the fly in the ointment as I have no idea what how the baffle would compare with a dunstall!

C M R CD C 2002 a young bloke had a Commando , with a TWIST ,

The Dustall set up with upswept tailpipes & stainless or C F cans .
As it was the latest dew cati hot sh*t super set up , I thought it pretty cunning .

Obviously , like any other Exhaust , combining the pulses reduces the amplitude or whatever it is ,
then the dual mufflers with greater aplob can silence it more effectively with less restriction, or
Impediment ! For Hot Sh*t .

2002 was WET , it actually had a alloy cradle & NSR monoshock & front end , Roadster tinware.Blacl ' paint ' .
Was the i think 18 yr olds ' Ride to work ' bike . Was real smooth and going past everything on the track like they were standing still .
Used good precise throttle control . Mostly W F O .

Any Kiwis find a picture of this , or know the dudes name . Must be top of results in his class . 2002 or 03 was the wet year?
Pukekohe

Had the mufflers set like this , mightabeen car mufflers .

' one ' can see how it adapts to the Dustall set up , No sweat . If modernisms your thing . Though perhaps Not Modern , Now .

850commando said:

sadly even in centres of higher learning and disciples like engineering there are individuals who squeak through because they passed the course material, but are totally inept when it comes to real life... the old joke, Hi! i'm an engineer and here to help comes to mind or was that Hi! i'm from the government...and here to help
we still say,
Those that can, do , those that can't, teach , and those that can't teach, consult...

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What myself ask on the seats of higher learning is, why so many people graduate with a degree in one subject, yet go and find employment that is totally different and nothing to do with what they spend all their time getting a Phd in, for example I know of one person who became a Dr. in English literature, got yet another doctorate in yet another subject, yet has being doing a job in a university for the last 10 years where he is responsible for the whole of the university’s computers!!!!

At least Dr. Blair achieved many professional engineering distinctions including:

He was a Chartered Engineer (CEng).

• In 1974 was made a Fellow of the Institution of Mechanical Engineers (FIMechE).

• In 1978 he was made a Fellow of the Society of Automotive Engineers.

• In 1982 he was made a Fellow of the Royal Academy of Engineering - a very prestigious award.

• From 1991-1992 he was Chairman of the Automobile Division of the Institution of Mechanical Engineers (UK).

• From 1993 to 1997 he was a Member of the Board of Directors for the Society of Automotive Engineers.

• From 1994 to 1996 he was a Member of the Technical Committee of the Royal Automobile Club and was their Chairman from 1997 - 1999.

• In June 1995 he was awarded a CBE in the Queen's Birthday Honours List.

Bernhard said:

What myself ask on the seats of higher learning is, why so many people graduate with a degree in one subject, yet go and find employment that is totally different and nothing to do with what they spend all their time getting a Phd in, for example I know of one person who became a Dr. in English literature, got yet another doctorate in yet another subject, yet has being doing a job in a university for the last 10 years where he is responsible for the whole of the university’s computers!!!!

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i'd say we are off topic ... but don't you wish you had possibly branched into other endevours throughout your working life? some of these stiffs just did it early on...

I worked with an old engineer who's advice was "engineering is the worlds greatest education, don't make it a profession" and now looking back i believe what we learned other than all the calculus, was how to solve a problem... which can be applied anywhere...


now back to the regular program of Dunstall 2-1-2

850commando said:

i'm still debating how i'm going to deal with the 2-1-2 exhaust and main stand once the Dunstall is reassembled.
i have read a number of comments that the dunstall stand for the 2-1-2 was flimsy and tipsy. current the bike only has the side stand which is badly worn and floppy, i may end up making a race style stand which utilizes the original main stand bushings and race type slide under lift.

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if, and I’m only saying if, you decide to use the 2-1-2 you might want to get them professionally re-chromed –you may then have the only Dunstall that doesn’t show signs of rust coming through