Two into one exhaust systems on a Commando

acotrel · Jul 2, 2024

I have previously made coments about gas flow not being the most important factor in exhaust system design. I suggest the Kadence effect also happen in exauhst sytsems on four-stroke motors. The comments about resonance effects and exhaust pipe sizes and lenghts in this video are interesting :

worntorn · Jul 2, 2024

I've only tried one 2 into 1 and that was an original but somewhat beat up Dunstall system.
The Dunstall ad for the system claimed it would knock a full second off an otherwise stock 850's quarter mile et.
That would mean an et in the high 11 second range. The Wallace racing calculator agrees with period tests in that a 58 crankshaft bhp machine weighing about 615 lbs with rider will et at about 12.8 seconds.
To knock a full second off the calculator says an additional 17 bhp is needed. Wouldn't that be nice with just an exhaust change?

The sound was fabulous and the seat of pants impression was good.
Unfortunately the measured performance on Dyno Hill wasn't great.
The Dunstall 2 into 1 produced only about half of the acceleration achieved with a stock pre Black Cap system.

I would like to try one of the other 2 into 1s to see if they work better than the Dunstall, or perhaps even better than a stock system.

Glen

hybridracer · Jul 2, 2024

worntorn said:
I've only tried one 2 into 1 and that was an original but somewhat beat up Dunstall system.
The Dunstall ad for the system claimed it would knock a full second off an otherwise stock 850's quarter mile et.
That would mean an et in the high 11 second range. The Wallace racing calculator agrees with period tests in that a 58 crankshaft bhp machine weighing about 615 lbs with rider will et at about 12.8 seconds.
To knock a full second off the calculator says an additional 17 bhp is needed. Wouldn't that be nice with just an exhaust change?

The sound was fabulous and the seat of pants impression was good.
Unfortunately the measured performance on Dyno Hill wasn't great.
The Dunstall 2 into 1 produced only about half of the acceleration achieved with a stock pre Black Cap system.

I would like to try one of the other 2 into 1s to see if they work better than the Dunstall, or perhaps even better than a stock system.

Glen

I made a copy of the Norton 2 into 1 exhaust from the 750 formula racer (another Dunstall/Blair QUB design I believe) for my 500/750 racer. That replaced separate pipes/megaphones and, subjectively, widened the power band without loosing any at the top end. The main advantages were in weight saving and it tucked nicely out of the way. I don't know of any other 2 into 1 systems being used on the Commandos.

worntorn · Jul 2, 2024

There's the Maney system.

ashman · Jul 2, 2024

When a new neighbour moved in across the road I knew he had a 750 Commando but it just didn't sound right, it had a 2 into 1 system on it but the muffler made it sound not right, it just lost that lovely note a twin system makes on a Commando, at the time I was on the last stage of building my Featherbed 850, he knew I was riding a 650 Triumph at the time and he came over to interduce himself, I said come with me and I took him up into my old shed at the time and as soon as he seen the 850 motor sitting on the engine stand on my work bench put a big smile on his dial, then we went over to his place and drank beers straight from long neck bottles.
We went for a ride next day up the Mt Mee range, he was a diesel fitter by trade, but to me his Norton just didn't sound right and lacked something in power, not sure if it was the 2into1 or something else going on, not long after he separated from his wife (drinking and gambling problem) and haven't seen him since, that was back in 82, his wife and kids live there for about 15 years, but I never seen him again.

Schwany · Jul 2, 2024

The 2 into 1 on my 750 does not sound like a Norton unless it is idling and even then one does need to use their imagination and look at the tank badge. Blipping the throttle it sounds like a 4-cylinder drift car. I would think the Maney system sounds similar, but is probably a bit quieter since it has to pass race track noise rules.

I need to get a Go Pro and a YouTube account, because I doubt anyone that isn't already ignoring me believes much of anything I say. If it isn't on video it didn't happen.

maaseyracer · Jul 2, 2024

The math in that video suggests for an 850, stock exhaust for peak torque at 4000 RPM, 1.5" for peak torque at 5000 RPM and 1.625" tubing for peak torque at 6000 RPM.

Most of what I have built exhausts for I have done a 2 into 1 setup, and have been slowly working towards an X pipe as I have wanted to try it. I not sure I have a the valves or the crank to support 6000 RPM peak torque, but I would play with 1.5" OD tubing.

baz · Jul 2, 2024

ashman said:
When a new neighbour moved in across the road I knew he had a 750 Commando but it just didn't sound right, it had a 2 into 1 system on it but the muffler made it sound not right, it just lost that lovely note a twin system makes on a Commando, at the time I was on the last stage of building my Featherbed 850, he knew I was riding a 650 Triumph at the time and he came over to interduce himself, I said come with me and I took him up into my old shed at the time and as soon as he seen the 850 motor sitting on the engine stand on my work bench put a big smile on his dial, then we went over to his place and drank beers straight from long neck bottles.
We went for a ride next day up the Mt Mee range, he was a diesel fitter by trade, but to me his Norton just didn't sound right and lacked something in power, not sure if it was the 2into1 or something else going on, not long after he separated from his wife (drinking and gambling problem) and haven't seen him since, that was back in 82, his wife and kids live there for about 15 years, but I never seen him again.

Just goes to show
Those 2 into 1 exhausts can also wreck your home life

Two into one exhaust systems on a Commando

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