Plan to install balanced pipes on my '73

In the next few days I will install the original-type balanced pipes on my '73. I have been wanting to try them for years and now have all the parts so I'll probably do it tomorrow and then take it out for a run. It's a matter of curiosity for me; I realize that most people say they are a problem as far as cracking/etc but I want to at least try the engine like it would have been originally.

Dunstall claimed a noticeable power improvement in balanced vs unbalanced but I don't expect anything from it. I will do some timed acceleration tests in 3rd gear from 2-6000 RPM to see if there is any difference between the balanced/unbalanced. It's the closest way I know of to do some somewhat scientific testing of changes. The butt dyno on it's own is more often wrong than right in detecting actual power changes, often confusing peakiness with increased power. The classic case of that is putting a too-large carburetor on an engine where it loses low end but then suddenly accelerates as the RPM get's high enough - the actual acceleration is less than stock but because there is now a hole in the power curve, the "sudden" acceleration feels stronger to the butt. I've seen a ton of cars where the owners claimed increased power that they could feel and the dyno/track showed a power LOSS.

In any case, as I said, mostly it's just a curiosity thing.

Mine came with balanced pipes, but after cracking the left pipe 3 times (repaired once, replaced once) I gave up and put on 750-style pipes with the corresponding exhaust nuts.

Replaced my mufflers last year, and found I couldn't get over 80mph. Comparison of the old and new showed the new had a restrictor plate with a 5/8" hole in the center. This would have been fine with a balanced exhaust, but too restrictive with separate pipes.

I took a Klein stepped drill bit with a 12" extension, and drilled these holes out to 7/8" - Now I can go as fast as I want. (5/8" hole is about .307 sq in, 7/8 hole is about .601 sq in).

Dependent on how your carbs are set up, you may need to richen your mixture if you use the balanced pipes with your same mufflers.

I had balance pipes on my bike since new with no cracks. I kept one of the crossover pipe clamps loose because the bolt was so frozen I couldn't tighten it.
It never cracked. It did finally break the flair on the left pipe though.
I do like the look of the balance pipes

My '75 still has the original balanced piped exhaust. It cracked a bit at left side curve just above the balance pipe itself. Once welded it's been fine for about 25 years now . A bit of the chrome plating actually flowed into the repair so no rust either. I think the biggest thing you'll notice, depending on your mufflers if you have straight through pea-shooters, is the sharp crack of the exhaust note will be softened a bit. Something I actually appreciate.

If you get a power increase, it will probably be due to exhausting through two mufflers on each firing instead of only one - less back pressure. The bike will probably be quieter, and I suggest that might have been the reason for the crossover in the first place. If your mufflers are straight through with no baffles, I don't think you will discover a difference unless the bike goes slower because the harmonics are stuffed up. I've always liked those fish-tails they used to use at Brooklands in the 30s.

Balanced pipes are installed and bike run up on the center stand. I have to admit that my initial impression - totally subjective since I don't have a Db meter here - is that there is no difference in sound volume from the peashooters, at least when at idle/blipping the throttle. It may be different under load. Unfortunately, I have other things to do today so a ride is not possible - maybe tomorrow but not sure; it's my wife's birthday. She likes riding ('12 BMW F650GS) but we have other plans as well so possibly no ride until Tue.

But one thing I DO like for sure - I think the bike looks "meaner" with the balanced pipes. I like the look! I'm sure others disagree.

Strange co-incidence!
I just fitted an original balanced system on my MkIIA, but I also fitted the 'correct' black-cap silencers.
Partly because I had the pipes and silencers already, and partly because I'm curious as to how they performed 'out of the crate'.
As I use the bike a lot with my son or daughter on the back I'm happy to sacrifice a bit of go for a quieter life, and it's certainly quieter!
Once I've got new carb rubbers fitted (old ones showing their age) I'll get some miles on it and report back.

I also think they look pretty good

Did a 140 mile ride yesterday with my "new" balanced pipes.

I did nothing to the carbs after installing the balanced system and during the ride - twists/straights/up/down from 6400 feet to 8500 feet - it was clear that the carb settings/jets are leaner than they were with the straight pipes. There is a lot of popping on coast down that did not exist perviously and there is now a very noticeable flat spot if the throttle is wicked to WOT under load.

So a richer adjustment/jetting will be needed which, in turn, indicates there should be a slight power increase compared to the straight pipes. But, since this was stated re balanced pipes back in the early '70s in Dunstall's tuning book, that's really not new information.

The popping on decel would be an indication of a too lean condition at the idle mixture screw. Try turning them both in a bit. Your idle may get a bit rougher and fall a little so you may have to raise it a bit to compensate. On my bike,when the pilot screws are set to an smooth almost Honda like idle (quite lean), It runs badly at anything off idle and pops a lot when off the gas. Richening up the idle mix lost me that idle but bike runs absolutely stellar everywhere else and the over run is just an even burble. Flat spot when opening the throttle is a symptom of a too lean slide in the book, BUT, I doubt that would be the issue in your case as balanced 850's all came with 3 1/2 slides, probably what you have already. You may find richening the idle mix solves your new running quirks. Richer mains won't do anything to stop the popping or flat spot but they may still be needed for correct high speed metering.

My bike was originally fitted with a balanced exhaust system.
However, my experience with aftermaket balanced systems, was that these were a very poor fit.
Itwas almost impossible to fit these pipes in such a way that they were not under stress,and the new pipes cracked in no time at all, so i decided long ago not to bother and fit an unbalanced exhaust system, and I never looked back.
Initial experience was that the noise level went up a little bit though.

Ditto that, the popping may well be caused by an air leak.

Yes, the popping could be an air leak in the exhaust itself though I checked all that very carefully and don't believe there is one.

As far as fit - the oem balanced tube system fit with no strain at all. In fact, I was surprised at how easily it all went together. With the header pipes tightened into position, the balance tube connectors would still easily slide back and forth between the header pipes/tube which showed that the pipes aligned perfectly and that there was no strain applied by tightening the balance tube assembly.

As I said earlier, I couldn't really tell any difference in noise volume while riding the bike.

I like balanced pipes. To live with them so far, and prevent cracking... I've compromised. Thermally ... the mechanical set up is crazy. The hot head expands and the steel pipes do so.... but less than the head. If you constantly flex rigid clamped up steel pipes then who is actually surprised they break?
I only clamp up the balance pipe on each end... at one side of each end joint. The other bolt for show only.
Well lubed up with hi temp nickle based anti seize, this is my standard assembly routine and so far (since 1995) I have not had cracked balance pipes. More power(if tuned)...quieter....what's not to like.

I am just now putting some on a friends MKIII, and they fit fine. I did learn you must change the whole black cap bracket set-up to earlier peashooter brackets. My 5 mile late MKIII also came this way...peashooter muffler with earty style peashooter brackets. Not as MKIII factory parts list shows....

"
Well lubed up with hi temp nickle based anti seize, this is my standard assembly routine and so far (since 1995) I have not had cracked balance pipes."

Hmmm...that's a good idea - I put a good smear of anti-sieze on the connectors but it didn't occur to me to allow each side to "work" with expansion. I'll be loosening one bolt on each connector!

Good luck with that - as soon as you hear any popping and banging you'll know where to look. !
We notice Dave didn't actually say how many miles he has done to test this setup,
and if the antiseize ever cooks off and loses its zing.

We still haven't seen a dynochart anywhere to show there is any torque advantage to this setup either.
The siamesed pipes that dommies had back in the early 60s were actually faster than the twin separate exhausts,
and Nortons quoted the dyno figures to prove it.
Under 4500 rpm there were a few less ponies though, so it didn't suit everyone.

Be interesting to see a decibel chart for balanced and unbalanced pipes too.
Although peashooters vary somewhat internally these days anyway.

Re a Dyno chart - I agree, I have never seen one. All I have seen are Dunstalls statement that there was an HP gain and the balanced exhaust was his recommendation at the time for optimum power on a Commando street bike - several years before Norton adopted it.

Also, the fact that my engine is now running leaner at the mid range/top end than it was with regular pipes says the engine is receiving insufficient fuel for the amount of air now pumping through the engine. So increasing the fuel appropriately means more/fuel/air being burned per combustion cycle = more power.

Whether that adjustment will make any noticeable difference, I have no idea. Spark plugs are showing much leaner now as well...

It'll be another week before I have a chance to mess with the carbs. At the moment the needles are on the leanest (top) setting and the jets are 240s. These worked well with the oem pipes at the approx 7000 ft altitude where the bike lives. I plan to raise the needles a notch/try 250 mains.

mike996 said:

All I have seen are Dunstalls statement that there was an HP gain and the balanced exhaust was his recommendation at the time for optimum power on a Commando street bike - several years before Norton adopted it.
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Click to expand...

Dunstall pipes, as they supplied them though were that fancy 2 into one into 2, that went down under the engine.
These were proper tuned length pipes, didn't QUB (Queens University Belfast) do the testing that produced these.
And the Dunstall Decibel 'silencers' fitted.
So that wouldn't be the balanced pipes as Nortons later produced. ?

Replying really late to this thread. Dunstall sold the Blair designed 2 into 1 into 2 exhaust later. Early on they made a conventional balanced exhaust, it's pictured in Dunstall's Tuning Notes book with the claim that it was the best system for a street Commando.

ewgoforth said:

Replying really late to this thread. Dunstall sold the Blair designed 2 into 1 into 2 exhaust later. Early on they made a conventional balanced exhaust, it's pictured in Dunstall's Tuning Notes book with the claim that it was the best system for a street Commando.

Click to expand...

At the time, stock pipes were unbalanced individuals. (I'm sure we all know a few of those :lol Later, factory balanced pipes were similar. The theory is that the balance pipe would allow exhaust pulses from opposite cylinders help extract more volume from the next-door-neighbor cylinder. But the crossover pipe also gets hot and the cylinder head doesn't receive a flow of cool, clean air, raising it's temperature and lowering it's efficiency, especially in a hotted-up motor. The Blair exhaust does the same thing only better and with less hot air on the head.

Concept of expected behavior of 2-2 vs 2-1, good parts after 3 min mark
http://www.dailymotion.com/video/x6xpmh ... e-2-i_news