mike mcmanus said:
Having just had a minor exhaust pipe experience I have been pondering the relative benefits or disavdvantages of having a balance pipe between the two header pipes.
They
do exist, no doubt ....
mike mcmanus said:
We all well know the problems that are related to vibration and exhaust pipes, I think just about every balance pipe I have seen has been welded after cracking due to vibration.
Never had any problems with mine on a Mk.III - after approx. 76,000 mls, they were still in excellent shape (stainless). However, there are some replacement (pattern) versions out there with mis-aligned balance-pipe connectors - they are out of angle and thus mounting the balancer pipe
forcefully means to put them under permanent torsional stress, which makes them crack after a while.
Otherwise - when perfectly alligned
and mounted appropriately, vibration desn't seem to do them any harm - the exhaust system as a whole can follow the engine's "isolastic" struggling due to the elastic rubber mountings of the silencers.
mike mcmanus said:
Does a balance pipe benefit the perfomance and does it contribute to smoother running :?:
The balancer pipe effectively
doubles the complete exhaust volume available for each cylinder. Contrary to the un-balanced "one cylinder, one pipe, one exhaust" system, exhaust gases are offered the volume not only of
two silencers, but also of
two pipes, since the balancer pipe is located closely to the the twin exhaust ports.
This
reduces exhaust noise somewhat, but, more importantly, it
reduces exhaust gas back-pressure in the mid-to-high RPM range, and thus also somewhat
reduces heat stress on the cylinder head's exhaust side.
However, if you're not using a "hot cam" and if you don't ride your Commando at the rev-limit most of the time, you'll barely notice the effects of these improvements and you might thus consider them negligible. Otherwise, there are unbalanced 1.5" dia exhaust systems out there, easing exhaust gas flow a little.
IMHO, the non-balanced pipes look "cleaner", since they provide an uncluttered view at the engine's exhaust side. If you want to use such an unbalanced exhaust system on a Mk.III, you should be aware of it's unique dimensions: the left pipe's downward section must be approx. 1" longer to stay clear of the Mk.III's fatter primary drive side.