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#837082 01/17/21 6:10 pm
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Would unbalanced down pipes have an effect on the performance etc for my T140v "74" Mk1 carbs i'm running it with balanced at moment but thinking of changing to unbalanced your thoughts would be appreciated

Many thanks Dave


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I run my 72 unbalanced and with the old style sausage mufflers. Runs MUCH better. I switched it back to stock a while back just to see what it looked like.
Lasted about an hour.


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Thanks desco did you leave the joining rubber pipe on the carb to barrel inlets too ??

Thanks Dave


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Carbs still joined.


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Hi guys,
I never liked the look of the ex. balance at the head but thought I understood it's reason for being, my Dunstall swept backs had one at the head, a nice stainless flex tube and the bike ran well.

My question, for anyone knowledgeable, is this...is the X type connector vs. the H connector (before mufflers) or the cross pipe at the head type of equal efficacy? Less obtrusive (except for main stand issues) would be the H balance tube just prior to mufflers...just kind of thinking of future exhaust system.

Thanks David for the conversation...I hope someone sets me straight on balance pipes and types...Mark R.

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Photos of Triumph's "Thruxton" unit 650 Bonneville racers in the 1960s show them running with "balanced" exhausts.
Those "Thruxtons" were also the first with Triumph's dual leading shoe front brakes.
Like the balanced exhausts, they also became standard on 650 Triumphs beginning in 1968.

Whether the original reason for those balance tubes only had something to do with racing at high speeds is open to question.

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I suspect that the balance pipe is more about low-speed and idle smoothness.
It also helps to keep the pies in place on T140s and BSAs with the push-in pipes. Whose idea was that?


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Originally Posted by DavidP
I suspect that the balance pipe is more about low-speed and idle smoothness.

[Linked Image from images-na.ssl-images-amazon.com]

(1969 Exhaust System)

"With worldwide sound level legislation closing in on the manufacturer, and the sales climate demanding ever increasing performances, the next step on the precarious ladder of achievement of both ideals was the introduction of the coupled exhaust system...

...The improvement in noise level achieved allowed the home and general export market to utilise as standard equipment the sports straight-through absorption type muffler equipment previously reserved for the U.S. market for the preceding three years"

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With the balance pipe each firing stroke effectively exhausts into an exhaust system twice as big as if there were no balance pipe----hence lower overall noise levels.
But--also very useful for keeping the exhaust system in the head.

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The noise levels are generally accepted nowadays in the UK with these old thumpers as when MOT'd it's usually down to the testers discretion i would imagine with push over pipes the clamps work pretty effective. I managed to source a set of S/S unbalanced down pipes looking forward to trying them out.Another point is would be surely this would give a more clear indication of the mixture of each cylinder with the colouring of the pipes.


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If noise is not a problem then IMHO there is no downside in not using the unbalanced pipes.
Bear in mind that the noise tests back in the day were carried out in a fixed manner---well removed from everyday life.
If your MOT man approves it then great.
We dont have that concern over here in New Jersey--there is no testing of motorcycles.
The only constraint on noise is the opinion of the cops.
But most bikes here are Harleys and a lot of them are unsilenced and many of them owned by cops-- so no problem!
i have not heard of a motorcyclist in NJ getting a ticket for excessive noise.

However judging your carburation from the coloring of the pipes is a bit of a blunderbuss approach---it would for example not discriminate as to what stage of the carburation was causing what coloration.
Best of luck with the bike!

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There is no doubt a properly placed balance pipe can increase mid range power.However 4 inches from the head might not be the proper place.....


79 T140D, 89 Honda 650NT ,61 A10 .On a bike you can out run the demons
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But a V8 engine is a good start for me
Think I'll drive to find a place, to be surly"
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Originally Posted by Hillbilly bike
There is no doubt a properly placed balance pipe can increase mid range power.However 4 inches from the head might not be the proper place.....

My thoughts exactly and saved me some typing. An X pipe further down the system would have a much better effect than the balance pipe right next to the head. Probably why some Japanese bikes had an expansion box between the two pipes and before the silencers, that way you don’t have to bring the down pipes close enough together to achieve a decent X arrangement.


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Someone...maybe it was Dunstall?...made a set of pipes that placed the balance tube further back, near the rear wheel.

That kind of agrees with Allan's assessment of where it SHOULD be, and WHY.

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My findings on the balanced exhaust systems is that for speed and torque, there's little in it compared to unbalanced pipes and straight through silencers. With the 71-72 silencers, or mufflers (as noted by a US bike magazine; "the British term silencer, is an exaggeration") a balance pipe may be useful, and for the later more restrictive long mufflers, a balance pipe is a must.
Noise may be reduced with a balance pipe and straight throughs, but sometimes they can set up resonances that is annoying to the rider. I've come across that a couple of times, but it does depend on how the mufflers are constructed.
Doug Hele put the balance pipe up by the exhaust ports for a reason, but I'm prepared to believe that it was the second best spot, and done as a compromise. Remember that the system was developed for the Thruxton, so must have had merit.
As an aside, I built an exhaust system for my 973cc R3 using 1 3/8" pipes but to the same configuration as the standard manifold. It had a nasty hole in the midrange around 4-5000 rpm that I couldn't tune out. I saw that the then new 900 Triumphs had a very similar system but featured a balance pipe underneath the gearbox. I placed mine in the bend in front of the crankcase because it was easier, but it worked. Experimenting with size and placement would no doubt have yielded even better results, but the bike went well and I was happy.

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Originally Posted by Stein Roger
a balance pipe may be useful, and for the later more restrictive long mufflers, a balance pipe is a must.


SR
Interesting theory that SR i'm running stock mufflers on at present (do like the sound)i do have a set of early T120 type to try though.Iv'e always thought that blueing of header pipes is generally caused by extreme heat passing through therefore weak mixture can result in this,albeit the best check is the condition of the plugs as this does indicate air/fuel mixture levels


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Originally Posted by Dave Lid
Originally Posted by Stein Roger
a balance pipe may be useful, and for the later more restrictive long mufflers, a balance pipe is a must.


SR
Interesting theory that SR i'm running stock mufflers on at present (do like the sound)i do have a set of early T120 type to try though.Iv'e always thought that blueing of header pipes is generally caused by extreme heat passing through therefore weak mixture can result in this,albeit the best check is the condition of the plugs as this does indicate air/fuel mixture levels
I too enjoy the sound of a standard T140 these days, but when I was (even) younger I couldn't get them loud enough!
Blue exhausts comes from heat, but there are different causes; mixture too weak, ignition timing wrong (retarded is usually worse), and hard use. Other factors are the quality of the chrome and the wall thickness of the pipe. Just the right amount of blue is, in my opinion, beautiful and indicative of a well cared for and well used machine.
A very restrictive exhaust system won't let the engine produce as much power, so I don't believe it will heat the pipes more. I could be wrong though.

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Two clues that a balance pipe was for performance were that both the Thruxton and the Dunstalls both had them at the head back when sound wasn't the issue it is now.

Dunstalls could be had in 2 types, one with balance tube at head and one without but with primaries merging in a Y just in front of the engine into a slightly larger OD secondary that then Y'd again under the gearbox and went to a Dunstall muffler on each side, my memory thinks that the Y type may have been considered the better performer but I don't know.

A Triumph with TT style pipes in 1 5/8" OD with an 'X' pipe under the engine with a small reverse cone muffler splayed out each side of the front tire would be nice looking but if 'just as effective' an 'H' connector would be easier to fabricate. I'm pretty sure that placement of the merge is important so just designing for aesthetics may be silly but for a stock looking Triumph it would be interesting to dyno a Bonnie with a straight balance pipe between the headers and just prior to the mufflers as this would be less unsightly then in front of the head...Mark R.

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About 5 years ago, a 70 Triumph with a 750 kit...I fabricated the cross over with a slip joint for disassembly. No comparison test but the engine ran very nicely...

16390008352_1d50ba7a64_c.jpg

79 T140D, 89 Honda 650NT ,61 A10 .On a bike you can out run the demons
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But a V8 engine is a good start for me
Think I'll drive to find a place, to be surly"
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That' a very nice job Hillbilly that it allows the very hot gases to move away quicker from the head in theory putting the cross over joining pipe a lot lower it also increases the air flow around the fins.Using stainless steel could cool the gases better than stock mild steel chromed headers too.
Very bloody nice indeed sir


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Originally Posted by Hillbilly bike
About 5 years ago, a 70 Triumph with a 750 kit...I fabricated the cross over with a slip joint for disassembly. No comparison test but the engine ran very nicely...
I made mine the exact same way on the Rocket, only forward of the cases. I'm planning to do your version on my Trident. It's running real well but I had a Hyde 3:1 when my R3 was a 750 and it pulled harder in the low to mid-range. Would be nice to replicate that while keeping the standard exhausts. If it works I'll be happy, if it doesn't work I'll still be happy, as I'll have learned something.
By the way, the Hyde system left a big hole in the midrange, felt like reversion. I tried other mufflers and different lengths, but gave it up.

SR

SCN_0016.jpg
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SR, years ago I had a T150, I put a three into one header on it...A huge hole in power around 4000 rpm....I fabricated balance pipes from one inch tubing and placed them about 16 inches from the head. It really helped but cut power very slightly on top end. I didn't eperiment with carb jetting......


79 T140D, 89 Honda 650NT ,61 A10 .On a bike you can out run the demons
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HEY. Hillbilly,

If your under-bike crossover will clear the center stand, that looks like the way to go.

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Originally Posted by Hillbilly bike
SR, years ago I had a T150, I put a three into one header on it...A huge hole in power around 4000 rpm....I fabricated balance pipes from one inch tubing and placed them about 16 inches from the head. It really helped but cut power very slightly on top end. I didn't eperiment with carb jetting......
I had a similar situation with the 3:1 header on my Trident. Felt like reversion to me so I put the needle clip in the top groove. Flat spot gone. laugh
BTW: BMW puts the crossover pipe down at the front of the crankcase on the air heads.


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Dave Lid at 7:27
Stainless steel has a significantly worse thermal conductivity than steel so the gases would stay hotter. As gases cool, their specific volume drops, so stainless exhaust pipes would have a higher velocity at their end than the equivalent steel ones would. That means a tuned exhaust for stainless would have to be different dimensions to a steel one, but the difference probably isn't that significant up the top end.


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