Dr. Blair 2 into 1 into 2 Exhaust System

I had one of them, put it on my Combat, advertising claimed some 5 more hp.

I remember liking the looks and the extra power, but also the hassle of no center stand.

Don't know who Dr. Blair was, anyone else here buy one of those exhausts back then?

The late Dr. Gordon Blair was quite a guy. I've enjoyed his technical papers and books on high performance engine development for years.

There's a good writeup on him here.

http://www.profblairandassociates.com/GPB_Tribute.html

Ken

1up3down said:

I had one of them, put it on my Combat, advertising claimed some 5 more hp.

I remember liking the looks and the extra power, but also the hassle of no center stand.

Don't know who Dr. Blair was, anyone else here buy one of those exhausts back then?

Click to expand...

I put this system on my '73 750 (MkV 220627) in '83. It has noticeable power gain at higher rpms. Same thing as you, removed it in favor of a center stand. The welds kept breaking as well on the pipes.

Yes, a respected name from the past.

For the Norton system, what were the dimensions, diameters, lengths?
Would be good to have them "out there" in the community.

I had the prvilige of meeting and corresponding with Dr. Gordon Blair. First met him while wrenching on my Norton Seeley in a parking lot in preparation for Daytona in 2005 and again at Daytona a few years later. He was always ready to help a racer. He designed the cam for the 500 Norton ultra short stroke that Herb Becker built for me. Great guy and great loss.

from lcrken's link:

By the end of the nineteen sixties Gordon Blair's research work on engines had produced validated computer simulation programs which were helping design more powerful engines and providing theoretical and design insights that were giving the Queen's University team advantages over even the biggest factory motorcycle teams. In 1969 these research and design efforts began bearing fruit when Queen's rider Brian Steenson finishing second to the great Giacomo Agostini in the 1969 Ulster GP at Dundrod on a QUB 4-stroke bike.

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Other merits of the system were clearance in corners and a beautiful sound. In theory the centre tube acts as a collector pipe as used on most performance V8 type engines which continues to draw exhaust gases out after the end of the exhaust stroke preventing burned gases from re-entering the combustion chamber due to valve overlap on intake. The top pipes that are welded to the flange that fix to the head are 1 1/4" ID pipe. The mid section uses 1 3/8 ID pipe and the final Y section uses 1 1/2" ID pipe. When you do the math the wall thickness is 1/16" so each piece is a snug fit into the next.I ran one for quite a while with only one Dunstall exhaust fitted to one side with no noticeable change in performance. On another thread Comnoz reported having no noticeable advantage with the system on his race bike and opted for a custom tuned set for his particular engine. I ran these for years in the 70's and 80's and never had any problems with breakages or splitting welds. I learned to fit them by assembling them loosely and then grabbing the middle section underneath the bike and shaking vigorously while pushing upwards, then tighten the header nuts, top pieces, mid section and finally the exhaust pipes in that order and using everything you've got to keep the upward pressure on the whole time. I never raced but did lots of 2, 3 and 400 mile road trips with zero issues. The biggest drawback for me was the low ground clearance which I learned to work around. Most used sets you see are dented on the bottom piece. I never used a center stand so that was a non issue and I didn't miss it.

xbacksideslider said:

Yes, a respected name from the past.

For the Norton system, what were the dimensions, diameters, lengths?
Would be good to have them "out there" in the community.

Click to expand...

Since you asked...
Here's the rough dimensions, keep in mind the camera perspective distorts a bit. Everything was placed at the inch marks of the edge of the tape. To replicate the system one would want a system such as this to copy from and a bike in situ to test fit to. There is tape residue on the ends so on the fitted shot of the complete system, 1st photo above, I didn't add any measurements as it wouldn't be accurate as when fitted to a bike.



To get the deflection on the middle section at 90' I supported the tube with sections of the other parts and then unceremoniously removed them in photoshop because the image was just too busy. The bend is about 6.5 inches (minus the diameter of the middle tube -1 3/8") so 5 .125" bend.

I had one in the 70's. Sounded great with Dunstall decibel silencers. Bike felt a bit quicker. Lack of centrestand was a real pain & it snapped at the welded joint just after cylinder head twice. I heard of others having the same problem. I gave up on it after the second failure & changed to peashooters.

Ian

The Dunstall 2-into-1-into-2 looks similar, are they related ?

Didn't the Dunstall have a special centrestand that let you keep a centrestand ?

One and the Same .

" 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.dunstall.com/

By Golly ;

" In April 1969, Paul added to his range of Norton Machines with a 750cc conversion to the 650cc Triumph. It used the existing cylinder head but with a different gasket, rings, gudgeon pins, circlips, 10:1 Hepolite pistons and light alloy barrel with lip-flanged steel liners. The Bore/Stroke was 82 by 75.5 mm yielding 740cc. A 0.020-in overbore gave 750cc and a 0.040-in overbore opened it up to 760cc. The 1969 catalogue featured an expanded range. It still included the 750 Triumph and the Dunstall Norton Sprint (Atlas), but also included a Dunstall Norton Export 750 based on the Atlas but designed as a racer with a top speed of 130 mph, and for the first time, the Dunstall Norton Commando. This had similar engine modifications to the Atlas versions and was fitted with twin hydraulic disks, a balanced exhaust system with 'Decibel' silencers, rear-mounted footrests, a 4 gallon glass-fibre tank and a new dual seat which replaced the Norton version. The machine also boasted a glass-fibre GT fairing and front mudguard, alloy top yoke and wheel rims. "

Thanks for the data. Took some trouble, it is appreciated. Love that last pic; I drooled over my Dunstall catalogue back when!

Back in the day, I slowly Dunstallized my 1971 Norton, ( Not Combat), First with the Hot Street Cam & 810 kit. Then with the 2 into 1 into 2 exhaust with Decible silencers.
It was pretty quick and I could always blow off the Harleys and most other Brit bikes.
But when I put the Dunstall head on with the re angled ,oversized valves, it really got fast. It had no problem with the 750 Kaw. 2 Smokes or the 1000 cc Kaw 4'cyl.
and it ran an 11.70 at New England Drag Way with stock street tires.
I always had problems with the exhaust threads in the head with the two into one set up. I think when the pipes got hot, that they pulled on the exhaust nuts too much. Also the single pipe under the engine & gearbox was always grungy. and the chrome peeled off the pipes in places.
When I went back to the stock two into two set up without the cross over. The bike was noticeably slower.

Back in the 1960s Brian Steenson on the QUB 500 Seeley in the 1968 I.O.M. TT

http://www.youtube.com/watch?v=0Yv6fXm2JBY

Looks related to a Greeves ?
Doesn't show the expansion chamber, which is where all the development and predictive work was paying dividends.
Not much to do wif a Commando ?! :roll: :roll:

Not Q.E.D. , Q.U.B. , the Lair of the notorious Dr BLAIR !

He was at it again . Just couldnt leave those Zorsts alone .
Damn Irishman . Where would we be without them .
Itll be the McCandless Bros NEXT .

Viking makes a copy of the Blair/Dunstall 2-1-2. I was going to order one but realized that the reduced ground clearance would make it a non-starter for me. The pipe would be crushed closed in the first 5 minutes after leaving the house. If the bike still lived in NY instead of San Miguel de Allende, I would have one.

I got Paul Bryant to make me a "Dunstallesque" 2-1-2 system but with peashooters.
The bends from the head are tighter than the original and I asked him to tuck the single pipe high up underneath the engine with the "y" piece sitting higher to the Z plates also and of course custom peashooters. The pipes went correctly 1" 3/8 to 1" 1/2 to 1" 5/8.

The exhaust note definitely is softer than stock, and it is possibly very slightly down on torque until it approaches 5,000 rpm but then the exhaust note changes and it really pulls well up to the red line. Definitely more power than stock....it just seems to come on song beautifully around and after 5K.

The only issues that I've had are the pipes not sitting level when standing behind the bike (I've since got this sorted by altering the "Y" piece slightly), all connected together OK and never comes loose and has not cracked.

As my Photobucket links seem to have stopped working, it can be seen near the bottom of this page.
pictures-your-norton-commandos-t6210-165.html

Incidentally, I never thought it was a problem not having a centre stand except for when touring, and I didn't like to put excessive strain on my side stand with the tank bag and panniers loaded, so then I just re-fitted the standard exhaust and centre stand for the trip.

When in the workshop, I offer the centre stand up (whilst bike was on the side stand) and loosely put the bolts and spacers in but without the spring and you can then put the bike on centre stand. That takes about 2 minutes.

Just my experience. :lol: :lol: