Though rare, while working on these bikes, I've come upon pea shooters that were not straight through, but rather internally baffled and quite subdued in the sound department. At the time we thought these might be original equipment pea shooters for the 850 before the black caps. They were not much louder than them. As a matter of fact I have a set of these currently doing duty on my TR150. They started out as replacements for the very thin walled and subsequently cracked original black caps on the MK3. They were bought from a Norton dealer around 1977 and they were little to no louder then the originals. If you were to look into the ends you would see a flat baffle maybe 3 or 4" in with 3 smallish notches at the end of the pipe for exhaust. Outwardly they look like any other pea shooter. Anybody own a bought new -'74 850 who has or remembers the original mufflers?
The uncrossovering of the 850
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Biscuit said:
That's interesting Biscuit. The MkI of 73 is the machine in question with its balance pipe and pea shooters. Late 73 the MkIA appeared with black caps and black filter box. So if the baffled pea shooters were fitted to the MkI, it would make sense regarding noise reduction, including the balance pipe fitted to the MkI.
I think L.A.B. is right, in that Norton were more interested in noise reduction than any increased power or torque. But a balance pipe is known to improve performance slightly. My mate Sandy at Staintune has spent years power testing exhaust systems but he says the balance pipe really needs to be further down the exhaust flow.
Phil
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L.A.B. said:
And I guess one other issue, the balance pipe is BLOODY UGLY!!
Just in my humble point of view.
Phil
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baz said:
85 mph! My Atlas with separate down pipes nearly does that in 2 nd gear!
My suspicion is Norton fitted the cross tube for noise reduction, and they fitted it close to the head to enable someone with a grinding tool to enter the main pipe and smooth out the welds and any protrusions of the cross tube into the mainline.
As Yates says....further down the mainline would be preferable for a power boost, but that would involve more manufacturing headaches.
I think we have beat this one to death!
Slick
Reportedly Doug Hele had noted that the location of the crossover didn't seem to make any difference.
Up near the head is about the only convenient place on a parallel twin, there are bits in the way about everywhere else.
I had an 850 Mk1 back in the 70s, and it had those straight through peashooters with only the flutes in the walls,
AND the little mutes in the end of them - town and country style.
Exactly as in the 850 parts book, so those were the factory fittings.
Those internally baffled peashooters were the Campbells aftermarket type ?
This is the Commando dyno chart in Mick Duckworth.
As noted before, no idea when or where these were done, or if they were stock bikes.
Lookit that 850 torque curve - and note the torque is scaled different to the hp calcs.
Someone did a lot of work on an 850 to get a flat curve like that.
Look too at the Combat curve, which keeps on giving after the others have petered out - up into the red zone... !
Thanks to Mick for the loan of his dyno charts.
Up near the head is about the only convenient place on a parallel twin, there are bits in the way about everywhere else.
I had an 850 Mk1 back in the 70s, and it had those straight through peashooters with only the flutes in the walls,
AND the little mutes in the end of them - town and country style.
Exactly as in the 850 parts book, so those were the factory fittings.
Those internally baffled peashooters were the Campbells aftermarket type ?
This is the Commando dyno chart in Mick Duckworth.
As noted before, no idea when or where these were done, or if they were stock bikes.
Lookit that 850 torque curve - and note the torque is scaled different to the hp calcs.
Someone did a lot of work on an 850 to get a flat curve like that.
Look too at the Combat curve, which keeps on giving after the others have petered out - up into the red zone... !
Thanks to Mick for the loan of his dyno charts.
The balance tube has always made me wonder..........
It is my understanding that the tuning guys (dunstall, CNW,) use a 1 3/8 pipe out of the head about 14" in length,
The proportions and proximity of the MK3 crossover seem to have the exhaust volume opening up way too early.
I don't know much about exhaust pulses or that super technical stuff, but for performance, the factory cross-over seems counter productive.
The whole concept to me looks like a pseudo-expansion chamber starting about 6" from the exhaust valves.
I always figured that they put it where they did, not for the optimum functionality of the system, but rather because that's where it fit.
(P.S. I Got rid of the balanced exhaust on my MK3 20 years ago. )
It is my understanding that the tuning guys (dunstall, CNW,) use a 1 3/8 pipe out of the head about 14" in length,
The proportions and proximity of the MK3 crossover seem to have the exhaust volume opening up way too early.
I don't know much about exhaust pulses or that super technical stuff, but for performance, the factory cross-over seems counter productive.
The whole concept to me looks like a pseudo-expansion chamber starting about 6" from the exhaust valves.
I always figured that they put it where they did, not for the optimum functionality of the system, but rather because that's where it fit.
(P.S. I Got rid of the balanced exhaust on my MK3 20 years ago. )
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An't read much of prior post but a simple crossover is mainly known for lowering exhaust tone and bark and more low-mid torque d/t two exits of less resistance. To get the best out to them- dual exhausts hot roders draw cranyon mark down each pipe then see where gets hotest quickest then cut holes and connect cross over. Usually stuff in the way so about awhere along exhaust pipes pays back detectablly. W/o special placement there is not much to do with tuned Y exhausts using opposite jug blast to pull out the next one.
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Rohan said:
Well I don't know who 'they' were, but the 850 torque curve on Mick Duckworth's graph shows '830' torque peaking at around 3,000 RPM and then tailing off above that figure which appears to be somewhat at odds with other published graphs and figures that have 850 max. torque at 5,000 RPM. In fact I'd go as far as to say the torque curve on that graph looks as if it could have been drawn back to front.
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The crossover in the 850 exhaust was not done as an aid in tuning. At least not pulse tuning.
It was simply there to relieve the back pressure that resulted from restricted peashooters or black cap mufflers that were mandatory in some markets.
If you are running unrestricted mufflers then the crossover does not seem to make much difference from what I have seen.
If you run the restricted mufflers without a crossover the bike will run hot and the engine will struggle to turn over 5000 rpm. Jim
It was simply there to relieve the back pressure that resulted from restricted peashooters or black cap mufflers that were mandatory in some markets.
If you are running unrestricted mufflers then the crossover does not seem to make much difference from what I have seen.
If you run the restricted mufflers without a crossover the bike will run hot and the engine will struggle to turn over 5000 rpm. Jim
L.A.B. said:
The graph would be just as mysterious if it were drawn reversed ?
Seems a heck of a jump in some places by the 850 from the previous versions of 750's.
Thought I'd try drawing the torque curves and power curves to the same scale, for a better comparison.
And see if your reversed idea can be made to fit.
And why the OP here back-to-back dyno charts will be somewhat interesting to see, and welcome.
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comnoz said:
Jim
Sounds like a good reason to get rid of an eye sore that's doing nothing but relieve clogged mufflers, unless you are of course using clogged mufflers. Anyone interested in performance would not be sporting bean cans.
Phil
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Yep or messing around on later extra heavy and fragile complex 850's.
The splayed out exht ports has prevented almost anyone fitting a one piece solution but I found on Peel with the header lengths meeting about bottom frame bend in normal bend back section they were springy enough to spread the port splay and snap in with some manly muscling. In Peel case was like drawing back a 60# bow and hold steady to aim a second or so - if not they can spring apart partically engaged trapped in threads to hang up so then have to grind flanges across threads to finish. Another hobot one in a row Peel feature, one piece 2>1> into what ever ya want from there back. With a longer runs to the 'joint' it would be rather easier to spread- aim- clear to fit/remove and likely add some softer deeper sounding more low down grunt as longer tubes are known for and Peel enjoyed by taking a good bit of the hollow megaphone bark out down low by combined back/back jet blasts seems to have assisted each other exiting about a foot beyond end cap.
[video]https://www.youtube.com/watch?v=Y0Va3sDhqwI[/video]
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hobot said:
Yep or messing around on later extra heavy and fragile complex 850's.
True hobot, or go one step further and say messing around with Commandos at all. But we do because we love them and they have attributes offered by no modern bike. If we didn't love them we wouldn't ride them.
I noticed another thread in here with no end of descriptions about how to start your Commando, not to break your side or centre stand at the same time, how to do it with damaged legs etc etc. One bloke even hangs off the side of trucks to get up speed before dropping the clutch for a start. Some folk are very slow learners, there is an alternative.
So hopping up a MkIII, retaining its obvious advantages but getting more performance at the same time is an interesting project. The discussion so far on the balance pipe has been very informative to me. It would appear it is achieving virtually nothing if retained with less restrictive mufflers than bean cans fitted. So keep it or chuck it I guess, performance wise it matters not. Noise wise marginal. Appearance wise? Chuck it, for me anyway. Staintune will design an entirely new header pipe system for me if I want, with a balance pipe further down the exhaust flow, and then mufflers to match. But it becomes impractical.
Phil
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