The uncrossovering of the 850

Original system on my 850, but when I had it off a while back, I could not get the crossover pipes to seal properly at the joints. I thought about using some sealant to stop the popping on overrun but then I decided that it was a pain in the ass to have this setup anyway.

So I swapped to the 750 style and got the long exhaust nuts on there. No doubt there is benefit to having all those threads engaged.

The bike seemed to like it, also. Throttle response seemed more accurate and sensitive and the engine ran great. Interestingly, I leaned it out about 1/8-1/4 turn at idle.

I dynoed the bike awhile back (when it had the crossover system) and posted a chart on the forum. I will dyno it again in the next couple of weeks and share the results.

I think it sounds better this way. Very cool burble on overrun and no popping.

Interesting report, thanks.
Look forward to some dyno chart time.
Popular mod, these no crossover pipes.
Nice cycle

IF IT GOES AS WELL WHY BOTHER DYNOING. Dyno does not indicate have well it performs on the road. It just gives you figures for whatever rev you measure at.

How much that cross over pipe was just marketing speak and how much it actually provided 'more torque'
has been the subject of a lot of speculation over the decades.
We'd welcome a true back-to-back comparison from someone committed to providing real science to the discussion...

I have to dyno it to see what is different and if my butt dyno is calibrated correctly.

This is a Dynojet 250i with load control and a sniffer. I'll toss it up there and do the standard acceleration run in fourth and then I'll probably run the sniffer to see what's what. I never sniffed it because of the leaky crossover. But I could do load at 2000, 3000 and 4000, running 1/4, 1/2 and full throttle at each, and get a hole lot of info. Unfortunately, I have a full time job! So I'll just zing it from 1800 to wherever I feel like I am not making enough progress for the noise.

The throttle feeling is something you don't get on the dyno, you are right. But I do think that if you accurately mark part-throttle increments, getting more power at the same throttle setting would likely mean it felt more crisp and responsive.

Why guess as no one here but maybe me will believe any seat of the pant performance metering especially after spending on an upgrade.
https://www.google.com/#q=motorcycle+performance+meters

Copper Hi-temp silicone on the threads and end of issue-poppings/back -offs etc.

kerinorton said:

IF IT GOES AS WELL WHY BOTHER DYNOING. Dyno does not indicate have well it performs on the road. It just gives you figures for whatever rev you measure at.

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Well I repectfully disagree.

Provided the dyno is set up and working properly and the operator knows what he is doing there will be a direct relationship between the results and performance on the road.

I would be very interested in back to back dyno numbers for single and connected pipes. My reading has seen people claiming better mid range with the connected pipes and also better noise control.

If both or either of these are true I would be interested in applying it to my own bike.

Rohan said:

How much that cross over pipe was just marketing speak and how much it actually provided 'more torque' has been the subject of a lot of speculation over the decades.

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As far as Norton's "marketing speak" was concerned, the balance pipe was fitted: "...in the interests of noise reduction".

Where do you get that quote from ?
Although we are not denying that, that was always part of the package.
But the sole reason ?

There was talk at the time too of a torque increase. ?
And 850 dyno charts around do show a fair old torque increase for the 850, over the 750.
But no back-to-back comparisons

Rohan said:

Where do you get that quote from ?

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"The NEW BIG NORTON" NV press release, Motorcycle Sport, April 1973 (reprinted in: 'Norton Commando Gold Portfolio').

I'm not sure the factory ever claimed it was done to "increase torque" but perhaps you can quote the source of your information?

I'm pretty sure its in Phil irvings Tuning for Speed.
Have to dig it out and have a search.

If one googles 'motorcycle exhaust balance pipe torque' gives about 7.9 million replies.
(Triumphs and Guzzis and BMs and Harleys and others also used balance pipes)
Many quote that increased torque and reduced sound comment.
Its also mentioned in there that Doug Hele was one of the first to design/use balance pipes,
to both reduce sound and find some more torque/power (in Triumphs).
He (supposedly) quotes that that the dimensions of where the balance pipe is located
"makes no difference at all" and "he had no idea why it worked".

The dyno chart in Mick Duckworths book on Commandos does show the 850 is a lot stronger in the low rpm dept than the 750,
far more than +83 cc should produce (745cc vs 828 cc).
Unfortunately, it doesn't attribute exactly when/where the dyno runs were done
(all the same dyno, for example ?)(all utterly stock bikes ??).

L.A.B. said:

Rohan said:

Where do you get that quote from ?

Click to expand...

"The NEW BIG NORTON" NV press release, Motorcycle Sport, April 1973 (reprinted in: 'Norton Commando Gold Portfolio').

I'm not sure the factory ever claimed it was done to "increase torque" but perhaps you can quote the source of your information?

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Triumph added a balance pipe back in 1969, long before noise reduction became an issue. I presume they did this for performance reasons, but have no information to confirm this. My original Dominator had a siamese exhaust system which I changed to twin pipes and actually lost power, just a feel thing, not dyno confirmed. I have one MkIII with balance pipe and one without. But one has peashooters and single Mikuni whilst the other has bean cans and twin Amals. So comparing apples with apples isn't possible. The bean cans will be dumped for peashooters and Amals dumped for twin FCR's, so I'll never know the truth re the balance pipe. But will retain it on Jim Comstock's opinion of its contribution to increased power.

Phil

phil yates said:

My original Dominator had a siamese exhaust system which I changed to twin pipes and actually lost power, just a feel thing, not dyno confirmed.

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The Dominator Portfolio Book tests that Dommie with a siamese exhaust (which is different to a balance pipe system, note),
and also runs an article from Vic Willougby (MotorCyclings Technical Editor).
Nortons claimed a few more hp from the siamesed system, but only above 4500 rpm,
and Vic Willougby confiirmed this by lapping MIRA (banked oval) at quite some speed...

I've had a few bikes with balance tubes, and keeping them leak free has been a bit of a battle at times....

Rohan said:

I'm pretty sure its in Phil irvings Tuning for Speed.
Have to dig it out and have a search.

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But that's not exactly "marketing speak" :? . Marketing speak would imply this to be a claim made by the Norton factory.

Rohan said:

phil yates said:

My original Dominator had a siamese exhaust system which I changed to twin pipes and actually lost power, just a feel thing, not dyno confirmed.

Click to expand...

The Dominator Portfolio Book tests that Dommie with a siamese exhaust (which is different to a balance pipe system, note),
and also runs an article from Vic Willougby (MotorCyclings Technical Editor).
Nortons claimed a few more hp from the siamesed system, but only above 4500 rpm,
and Vic Willougby confiirmed this by lapping MIRA (banked oval) at quite some speed...

I've had a few bikes with balance tubes, and keeping them leak free has been a bit of a battle at times....

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The Siamese system was found to make more power on the Dominators that came before the downdraught head. After the downdraught head, (650SS, later models of 88ss) separate pipes were the preferred exhaust.

Glen

According to jet mixing theory (BTW....I consider myself an expert in that niche of science, having used it in my doctoral thesis), the crossover tube functions like a 2 into 1 exhaust arrangement, but the scavenging effect is much reduced owing to the limited area shared by the two exhaust streams.

jet mixing, or entrainment, works by the action of viscosity acting over an area shared by two fluid streams moving at different velocities. The area of the crossover tube is much less than the area of siamesed pipes, thus the entrainment is less, all other factors being equal.

I would expect the position of the crossover tube to have little or no effect on the amount of entrainment, except if the tube is very close to the head, as it is (or was) in Whitworth Ranch's Cdo. Close to the head, the little entrainment that occurs with the limited shared area, is further negated by the smaller volume of gas between the exhaust valve and the crossover tube junction. The volume of gas downstream of the junction, is a poor target for entrainment as a reversed flow is necessary to entrainment it.

In summary, theory says some increase in power can be achieved by a crossover tube, but don't expect too much.

Slick

PS: Any reduction in exhaust back pressure gained by the crossover tube can be potentially erased if the joining of the crossover tube to mainline tube is poor quality...I.e., weld slag on the interior side of the joint, or cross tube protruding into mainline. Such flow disrupting imperfections might even increase the back pressure.

A few years ago when I worked on these bikes, customers who needed exhaust pipes to replace ugly rusty bits would often opt for single pipes over the balanced units. Most already had various brands of straight through pea-shooters and when those same mufflers were used with the new pipes the exhaust gained a sharper report. Maybe it was a bit louder too but mostly sort of a "rap" was added at higher revs. My bike still has the original pipes, crossover pipe and all, and some Emgo pea-shooters. It sounds pretty good and is not loud. As far as seat of the pants power, in my opinion, no difference. I can see why the increases sharpness of the exhaust report from an unconnected system may make the engine feel more responsive though. (seat of the pants perception enhanced by the ears) Back in the day, I can't see Norton spending more money on an exhaust system for such a maybe slight gain on their stock motor. Most likely they had to do this for noise although the most compelling argument for power, I think would be, as others have said, would be to maintain power while exhaling through such restricted, black-capped mufflers. Just my thought's, not reading any books to back this up.

Biscuit said:

I can't see Norton spending more money on an exhaust system for such a maybe slight gain on their stock motor. Most likely they had to do this for noise although the most compelling argument for power, I think would be, as others have said, would be to maintain power while exhaling through such restricted, black-capped mufflers. Just my thought's, not reading any books to back this up.

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My thoughts exactly!

Slick

texasSlick said:

Biscuit said:

I can't see Norton spending more money on an exhaust system for such a maybe slight gain on their stock motor. Most likely they had to do this for noise although the most compelling argument for power, I think would be, as others have said, would be to maintain power while exhaling through such restricted, black-capped mufflers. Just my thought's, not reading any books to back this up.

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My thoughts exactly!

Slick

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The hitch regarding this theory of maintaining power with black caps fitted, is that the balance pipe actually appeared on the MkI 850 which still had peashooters. Black caps and black box air filter came out on the MkIA 850.

Phil