exhaust systems question

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richieschrein

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Apr 11, 2008
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i have 73 850 interstate presently with crossver pipe between cylinders could i use ehaust pipes without the crossover im told theyre more $ and more diffecult to find. not sure what changes if any it would have on performance please advise
 
The cross over pipes are considered to be a pain. They make taking the head off more time consuming and they will leak.
I used to live in your area and went to MAP for parts at a fair price.
Good Luck, Mike[/img]
 
The balanced pipe system was introduced on the 850 models from 1973 purely as a measure to reduce exhaust noise.

If the balanced pipe system is changed to unbalanced then you are unlikely to notice any difference in power output if you have peashooters fitted? And no jetting changes may be necessary.
 
Got rid of my balance pipes this year and switched to plain pipes. My 74 850 Mk 2A Interstate now feels a lot sharper to ride than it did (I have peashooters fitted).

As LAB says there is no need to rejet he carbs.

Getting rid of the balance pipe and fitting peashooters will certainly give you more power then if you are running with original blackcaps and a balance pipe (I have been quoted a much as a 6 bhp increase if you do both) and it is certainly easlier to get the exhausts off and back on if you need to do any work on the head!!

I have been told that the balance pipes were introduced as part of measures designed to reduce emissions for the US market but I don't know how true this is.
 
mike916sp said:
I have been told that the balance pipes were introduced as part of measures designed to reduce emissions for the US market but I don't know how true this is.
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I think it as actually done to comply with European (noise emission) regulations, and was the reason we (in the UK) eventually got the 'A' (IA & IIA) models in UK/Europe with the black airbox and black caps but the US continued to get the non-emission MkII model?

When I changed my unbalanced pipes to balanced pipes on my MkIII using the same peashooters I can't say that I noticed any difference in performance at all, except it was a little quieter at low revs.
 
I've swapped around. My impression was that low speed pick-up was a little more forgiving of throttle position with the balance pipes but nothing critical.

The differences between Mike's and L.A.B.'s experiences could be due to different black-caps. The originals were said to be not too restrictive but they haven't been around for more than twenty years so most of us have had pattern examples on.

The balance pipes were fitted to all 850s, even those with reverse cones but I think that their primary benefit was to noise levels with the Annular Discharges fitted.

I wouldn't hesitate to use non-balanced pipes. I've never come across anyone who has wanted to change back, apart for reasons of originality.
 
79x100 said:
The differences between Mike's and L.A.B.'s experiences could be due to different black-caps.
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Neither Mike nor I had the black-caps fitted though (see previous messages).
 
L.A.B. said:
I think it as actually done to comply with European (noise emission) regulations, and was the reason we (in the UK) eventually got the 'A' (IA & IIA) models in UK/Europe with the black airbox and black caps but the US continued to get the non-emission MkII model?
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On the black air box subject - has anyone any experience of getting rid of that and fitting K and N's or bellmouths. I think it may give me a bit more of a power boost. I'm not going down a camshaft change route at the moment - just looking at simpler methods
 
L.A.B. said:
79x100 said:
The differences between Mike's and L.A.B.'s experiences could be due to different black-caps.
Click to expand...

Neither Mike nor I had the black-caps fitted though (see previous messages).
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That would be correct - the bike did not have blackcaps fitted when I bought it. It did have original Norton peashooters though which I managed to stick a finger through when polishing them. Talk about corroded, only the chrome holding them together. Pattens on now - English ones though :D
 
Ages ago , when my rusty and often rewelded exhaust headers with crossover (balance ) tube needed replacement , I asked myself the same question .
So I made a valve in the crossover tube that I could open and close with a choke lever .
Riding at different speeds and keeping the thottle constant , If there was any difference in power , I should have felt the bike accellerate or decellerate while operating the valve . Well , I felt NO difference at all ! . ( mufflers where open peashooters )
 
thank you

im a commando forum virgin no longer youre response in a matter of maybe one hour was unreal youve helped me out but there is one thing that puzzles me im not sure what you would classify a pea shooter i feel a bit ignorant but when i bought the bike in 74 would it have had pea shooters in either case im convinced i can get the exhaust pipes i want thanks to all richie:D
 
Re: thank you

richieschrein said:
im not sure what you would classify a pea shooter i feel a bit ignorant but when i bought the bike in 74 would it have had pea shooters
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If your '74 model had peashooters or not would depend on whether it was originally a Mk I or MkII (normally MkII for '74) with metal perforated airbox, or an emission IA or IIA model that would have had black caps (known as bean cans in USA) and black plastic airbox? Generally the US models would be the non-emission MkI & II models for '73 & '74.

The 1975 MkIII would normally have had the black caps and plastic airbox for all markets, so no 'A' model MkIII.

Examples here show Roadster models with peashooter silencers/mufflers in the first five photos, and the last two photos show the black caps/bean cans: http://www.nortonmotors.de/ANIL/NCRoadster.htm
 
Rich
If you choose to use the pipes without the balance you may need to use the 750 style Pipe Retaining Nuts. The Threads are a little longer. The Bronze ones are nice as they expand at the same rate as the head. My two cents.
Cheers,
CNN
 
back to the peashooters

thanks to all who responded but one more time i have 73 commando interstate red and silver i bought the bike in 74 its gone everywhere i have it had 1000 miles on it im assuming the mufflers were stock wich they are straight funnel type halfway and just tapered in at the very end im still convinced from everyones input its cool to drop the crossover pipe with little or no difference :D
 
Re: back to the peashooters

richieschrein said:
assuming the mufflers were stock wich they are straight funnel type halfway and just tapered in at the very end
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There was another type known as the 'cigar' silencers/mufflers?

They would have been fitted as standard to '72-'73 Interstate only models: http://www.nortonmotors.de/ANIL/NCInterstate.htm 1st, 2nd and 3rd photos

The most commonly preferred replacements for all types are the peashooters.
 
Those 'cigar' silencers (short taper / long cone) are said to give the same performance as the reverse cones with long taper / short cone. Based on riding behind them, I think that they're a bit noisier.

By the way (and I think it's been asked before), who first referred to the reverse cones as "Pea Shooters" ? My pea-shooters were straight tubes with a mouthpiece. I reckon that a (large) pea in a Commando silencer would make some sort of whistle rather than an accurate missile launcher :)
 
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