Were balanced exhaust pipes used on late model 750's?
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lcrken
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Good question. The only parts book I have that shows both 750 (after engine 212278) and 850 parts shows balanced exhausts for the 850 and un-balanced (no crossover tube) for the 750. But you can't always take that as truth. The factory did produce variations that don't show up in the parts books. In the advertising brochures for 1973, the only picture of a 750 model is of the short stroke 750 engine in a red roadster, and it does not have the crossover pipe. Unfortunately, that picture appears to have been taken from a show model, and as near as I can tell, the factory never actually produced any regular Commandos with that engine for sale to the public. Maybe one of the listers here who was involved with the factory back then can offer some insight.
Ken
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trident sam
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In the early 80s I owned a late 750 Commando, it had a balanced system. I don't know if it was original to the bike, but in them days exhausts etc used to stay on the bikes till they fell off (in the UK at any rate). The idea of changing a system for the sake of it wasn't a consideration.
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Mr. Rick
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When it was time to replace my headers for my 850, I got the original style w the crossover, figuring it was a good idea performance-wise in addition to being stock.
As everyone knows, it's a PITA to deal with. Can the experts tell us if the crossover really does help? And if not, why was it introduced in the first place?
As everyone knows, it's a PITA to deal with. Can the experts tell us if the crossover really does help? And if not, why was it introduced in the first place?
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L.A.B. said:
In a way it was done to reduce noise.
The crossover was used on bikes with noise reducing, restrictive mufflers. [Like the black cap mufflers and the peashooters with the small thumb sized hole in the end]
The crossover allowed each cylinder to exhaust through two mufflers -making then quieter, yet flow about the same as a non-restrictive muffler with no crossover. Jim
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L.A.B. said:
No doubt you know better than I do.
So I guess two mufflers in parallel likely are a bit quieter than one.
My Mk3 with a crossover and un-restricted peashooters is still quite loud.
I do know that if you install a restricted muffler without a crossover it really kills the top end. Jim
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Well I don't know much about the particulars in restricted mufflers. Any restricted mufflers I ever had soon became unrestricted.
I do know that the explanation I gave concerning the crossover and restricted mufflers was something Brian Slark told me back when he was pedaling parts in Ca.
I do know that the explanation I gave concerning the crossover and restricted mufflers was something Brian Slark told me back when he was pedaling parts in Ca.
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comnoz said:
That's the early 750 type (a 1970 Norton service bulletin gives instructions on how to open them up with [Edit] a 13/16" (not 1-3/16") hole cutter on an extended drill bit!).
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As you said, the later 850 Mk2 (06-4609) peashooters had reduced (1-1/8" instead of 1-3/8") outlets. I don't know if there were any internal differences.
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I have some unrestricted short peashooters on my hybrid SS clone and they are LOUD!!!!! with lots of backing honk on off-throttle such as when one shifts.
I always thought any kind of connected exhausts, such as the 850 and early Dunstall crossovers had the potential to enhance performance via added extraction. Paul Dunstall and Gordon Blair obviously thought so when they produced the 2-into-1-into-2 pipes.
I always thought any kind of connected exhausts, such as the 850 and early Dunstall crossovers had the potential to enhance performance via added extraction. Paul Dunstall and Gordon Blair obviously thought so when they produced the 2-into-1-into-2 pipes.
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Danno said:
The subject has been discussed a few times, here's what 'ludwig' had to say in a previous discussion:
Balanced or unbalanced headrers?
What's the difference between these two? Was looking at complete exhaust from Commando Specialties for my 850. I see that they don't have the balance pipe between the two headers. Does this make a differnce in tuning or idling or anything else? I also don't see how they mount without the built...
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Danno said:
It will enhance performance if the mufflers are restrictive or if the crossover is in the correct place to work with the wave activity in the exhaust.
Unfortunately the 850 crossover is not in the right place to help with wave tuning so your not likely to see much difference unless you have restrictive mufflers.
There have been several threads here on the performance/torque aspects of balanced and non-balanced exhausts.
As far as we can tell, no-one has shown any back to back comparison dyno charts that nail it down though.
On otherwise stock bikes. Once there are too many mods, too many things to consider.
Even a published dyno chart which should have shown any differences was flawed, one of the torque curves was mirror imaged !!...
As far as we can tell, no-one has shown any back to back comparison dyno charts that nail it down though.
On otherwise stock bikes. Once there are too many mods, too many things to consider.
Even a published dyno chart which should have shown any differences was flawed, one of the torque curves was mirror imaged !!...
comnoz said:
Isn't Doug Hele in print saying it didn't seem to matter where the crossover is, the effect is similar.
Again, without any published dyno charts to back up this statement !
My guzzi has 2 crossovers in the exhausts, one just near the ports and another back under the gearbox.
Perhaps they were doubling their chances of quietening it down ?
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