# 4
After hours of testing, the only real advantage of useing a 2 into 1 Exhaust is the weight saving.
He went on to say ... No HP advantage was gained as there is no Extractor effect.
This is what I remember. I think.
AC.

I'm not sure I'd pay that. And you don't say what model this is for....

BTW, in the early 1960s a 2-1 was a FACTORY option exhaust.
Vic Willoughby took a 2-1 equipped 99 for a spin, and reported it was faster.
7 mph faster.
He was mystified it was an option over the standard 2 separate exhausts.

The factory figures quoted that the torque is improved at higher rpm.
Without actually quoting any outputs.
Lower rpm torque is slightly less, however...

So what were the Duntalls doing ??

Yes well I don't really put much faith in what someone says when they come back from a ride Rohan, do you ?
I also don't put much faith in Factory options, If they are any good I would think they'd be on the bike.
I do remember Dunstall was refering to Early 750s including the Commando.
I know I had this book around the very early seventies.
Hey I'm not arguing, just stating what Paul Dunstall said.
Perhaps, as with lots of things, things have changed.
Edit... Just found what I think is the book ....... Norton Tuning by Paul Dunstall, back in print at Andover Norton.

Vic Willoughby was the Technical Editor for the big magazine at the time.
And was quoting the factory rpm figures where the torque picked up.
And compared factory bikes for speed, at MIRA.

I'd say that was pretty conclusive ?
7 mph faster at over 100mph is a pretty fair increase in hp.

The torque was lower at lower rpm though, so for pobbling through the villages the 2-1 may not be so good.

P.S. I seem to recall the Dunstall 810 with 2-1-2 zorst was quoted at 133 mph.
They wouldn't have fitted it if the factory pipes were no different ??

Cheers.

http://www.eurospares.com/graphics/dunst750.jpg

From the link that Matt has supplied about racebikes, was this quote about the Dunstall 2-1 pipe.

This 750 Norton in the "drain-pipe" frame has a 2-1 high level exhaust developed by Gordon Blair. You'll notice the megaphone is fitted right at the collector - my friend Craig's dyno experience indicates this isn't the proper way to do things, and that is why my 750 Laverda racer has a large OD tailpipe between the collector and the megaphone (photo in the section devoted to my bikes). Photo from the 02 Sept 70 Motor Cycle. 64K jpeg file

Totally different setup to the option Norton 2-1 pipes for roadbike Dominators in the early 1960s.
Nortons obviously knew better how to do things...

Rohan wrote:They wouldn't have fitted it if the factory pipes were no different ??

Sure they would, they were after all selling these things

Jean

Don't think that Dunstall actually sold any exhausts like the 2-1 type pictured ?
And, after all, they said it didn't work !!

The 2-1-2 with Dunstall Decibel silencers was a mean looking bit'o'kit......

Rohan wrote:I'm not sure I'd pay that. And you don't say what model this is for....

BTW, in the early 1960s a 2-1 was a FACTORY option exhaust.
Vic Willoughby took a 2-1 equipped 99 for a spin, and reported it was faster.
7 mph faster.
He was mystified it was an option over the standard 2 separate exhausts.

The factory figures quoted that the torque is improved at higher rpm.
Without actually quoting any outputs.
Lower rpm torque is slightly less, however...

So what were the Duntalls doing ??

hi all,i think the 2-1 exausts offered by the factory in the 60s were what we called { siamese pipes } i think these pipes were aimed mainly at sidecar riders,for obvious reasons,not only norton but bsa too, from what ive read on 2-1 3-1 or 4-1 is that they improve mid range torque with a slight loss of top end hp

chris plant wrote:hi all,i think the 2-1 exausts offered by the factory in the 60s were what we called { siamese pipes } i think these pipes were aimed mainly at sidecar riders,for obvious reasons,not only norton but bsa too, from what ive read on 2-1 3-1 or 4-1 is that they improve mid range torque with a slight loss of top end hp

The magazine article that Vic Willougby wrote on the factory siamese exhaust fitted Norton Dommies (which is a 2-1 exhaust) quite clearly spelled out that the torque improvements were all at the top end of the rev range, according to the rpm figures that Nortons supplied.
Maybe sidecars drivers like to fang it anyway...

Rohan wrote:

chris plant wrote:hi all,i think the 2-1 exausts offered by the factory in the 60s were what we called { siamese pipes } i think these pipes were aimed mainly at sidecar riders,for obvious reasons,not only norton but bsa too, from what ive read on 2-1 3-1 or 4-1 is that they improve mid range torque with a slight loss of top end hp

The magazine article that Vic Willougby wrote on the factory siamese exhaust fitted Norton Dommies (which is a 2-1 exhaust) quite clearly spelled out that the torque improvements were all at the top end of the rev range, according to the rpm figures that Nortons supplied.
Maybe sidecars drivers like to fang it anyway...

The bike that Vic Willougby refers to, if my memory serves me correctly is an 88 SS.
The 750s that Dunstall sold exhausts for at first had a balance pipe just below the exhaust port (Atlas) later a 2-1-2 for a 750 Commando which was done in conjunction with Dr Blair at Queens university at Belfast.

Bernhard wrote:
The bike that Vic Willougby refers to, if my memory serves me correctly is an 88 SS.
The 750s that Dunstall sold exhausts for at first had a balance pipe just below the exhaust port (Atlas) later a 2-1-2 for a 750 Commando which was done in conjunction with Dr Blair at Queens university at Belfast.

Yes the Norton factory siamese exhausts were for the 88 and 99 models.
Interesting they didn't produce a version for the 750 models.

The 2-1 Dunstall that Matt appears to be referring to was the early 2-1 that Dunstalls tried.
http://www.eurospares.com/graphics/dunst750.jpg
(In conjunction with Dr Blair)

Their later efforts were a much more elaborate 2-1-2, as you say.
Which did give an improvement in power....

[quote="chris plant"][quote="Rohan"]I'm not sure I'd pay that. And you don't say what model this is for....

BTW, in the early 1960s a 2-1 was a FACTORY option exhaust.
Vic Willoughby took a 2-1 equipped 99 for a spin, and reported it was faster.
7 mph faster.
He was mystified it was an option over the standard 2 separate exhausts.Quote.

No disrespect to Vic Willoughby and their ilk, but I would take this statement with a very large pinch of salt, on the basic that there is no other scientific proof other than a reading of an everyday reading of a Smith’s Speedo! These are manufactured to within plus or minus 10% that means at 100 mph that is + 10mph or -10mph!
Even if is better than that, say, on the two bikes each Speedo is +3.5% and the other -3.5% --that’s 7 miles per hour difference accounted for. And then there is a whole host of other factors to be taken into consideration, the slower bike could be a Monday morning or Friday afternoon job, have the ignition set just a shade too far advanced or retarded… I could go on. These are hardly laboratory conditions to compare by, are they?
The only way I will believe that there is a difference between the two exhaust pipes (2-1 Siamese and 2-2) is if someone uses a more scientific method using the same bike on either an engine dyno or a rolling road on the same afternoon with exactly the same barometer pressure and the same air temperate and humidity with only the exhaust pipes changed. And only then can the two different readouts be compared.
As for Dunstall, what I have to say about his Norton parts offered, (and I naively have brought them in my younger days) is unprintable!
If any thing, his Dunstall road cam for a twin I purchased was so far out on the cam lobes that they bear no relation to the actual timing in his catalogue. When fitted, it made the bike slower!
His race cam was a flat grinded on every 5 degrees!!!…. A serious engineer?- I beg to differ.

Bernhard wrote:As for Dunstall, what I have to say about his Norton parts offered, (and I naively have brought them in my younger days) is unprintable!
If any thing, his Dunstall road cam for a twin I purchased was so far out on the cam lobes that they bear no relation to the actual timing in his catalogue. When fitted, it made the bike slower!
His race cam was a flat grinded on every 5 degrees!!!…. A serious engineer?- I beg to differ.

You are too harsh, after a few turns of the engine, those flats would have blended into a smooth curve

Jean

PS I must admit all of the stuff I bought from Dunstall looked a lot better in print and lasted a lot longer in my mind than in real life.

Bernhard wrote:No disrespect to Vic Willoughby .

This was at MIRA. (Motor Industry Research somethingorother.)
Speedbowl.

They had things called stopwatches, and would well have been the only place in Britain where the TRUE TOP SPEED could be established ??

P.S. The MotoGuzzi V8 500cc lapped there at a near constant 187 mph.
Full dustbin fairing of course.
Hands up all that don't believe that speed, out of ~70 bhp.
When the flag drops, the bullshit stops, the stopwatch doesn't lie........

You are too harsh, after a few turns of the engine, those flats would have blended into a smooth curve

Jean

PS I must admit all of the stuff I bought from Dunstall looked a lot better in print and lasted a lot longer in my mind than in real life.[/quote]

Sorry if you don’t agree with me, but if you think about it when you state ‘after a few turns of the engine, those flats would have blended into a smooth curve’…….I ask you, where does all the metal swarf go?
While we are on the subject ever seen the damage when a camshaft snaps in two while being ridden? Yes… it was from P.Dunstall!