Hitchcocks Forum

Have a bit of a dilemma.

On my 612 I have a goldie pipe fitted to it, even the slightest hint of baffling in the end pipe and it loses performance.

With no baffling whatsoever it runs best, as soon as you baffle the pipe you can feel that the performance suffers, and the engine just does not feel so lively, and my seat of the pants dyno tells me it is down on power.

The downside is of course the noise, it is very loud with no baffling so I try and ride responsibly - no big handfulls of throttle in built up areas.

Does anyone have a solution to this, is there a better pipe than the goldie silencer that is quieter but does not decrease performance.

On a word, no.
Physics is against you here.
There's a reason my racing machines are loud.

I assume you've waded through our hosts' selection of silencers! My normal recommendation would be a short bottle silencer of Indian provenance, though these vary in quality and degree of restriction.

Not knowing where yours came from, I have to say not all Goldie silencers are the same, I had one of our hosts' for my old Electra-X and it was just an absorbtion (i.e. straight through), no attempt had been made to recreate the internal baffles of the original BSA design, unfortunately. Even WITH the baffle supplied it was a bit much for my sensibilities. This was some years ago, I don't know if they still make them the same. However there are others around which do make some attempt to keep he insides authentic, that MIGHT be one answer. The one I use on Not A Fury came from - well, it rhymes with Bautocycle Bengineering. Still a bit loud, and it has spat out its extra baffle twice...

Looking further afield, I wonder whether something like a Supertrapp SC Elite from the US of A might work, they're tune-able, i.e you can vary the number of end discs which act as baffles - fewer discs, quieter exhaust (but more back pressure). more discs, louder, freer-flowing. The downside is that they're really silly money to start with, then by the time you have added exorbitant shipping and HMRC's wedge for a private import it's a lot less appealing. You might find a UK importer.

Hmm. Step forward those clever Chinese, who, apart from their attempts at world domination, have also found the time to come up with a nice stainless steel clone of the Supertrapp for about £70 a throw and free shipping on that auction site. If a private import from far Cathay still bothers you, there's a German supplier who imports them, then you only have to get one sent from the EU which will be fine for a little while yet. For a few £ extra, of course.

Here's one on my Electra Street Tracker proj, with one of our hosts' 20° angled pipe bends.



I'm surprised that a big bad 612 Bullet is so susceptible to a bit of baffle, but I think you will have to be prepared to lose a bit of oomph in the quest for less blatt. Would going down a tooth on the gearbox sprocket help recover some of the urge, maybe at the expense of a little top-end?

A.

My 612 almost immediately destroys then spits out any baffle material I'd care to use so i've just gone with the majorioty decision.

Some sort of Z-flow baffling would probably be best. Minimal restriction to gas flow but causing it to slow and turn before exiting the bike which would remove a lot of the crack. Probably not an "off the shelf" solution though.

If we're talking long-stroke >600cc singles, would a Panther M120 silencer, possibly opened out a little, be an option? It looks like they use 1 ⅞" pipes, so one would need sleeving down for the RE pipe.

A.

PeteF has it spot on.

One of the reasons* high performance engines make power beyond 1hp/ci , is by virtue of the correct lengths of intake and exhaust tract- by true definition, the TUNED length of these items. Any change, in this case, to the correct exhaust length via a baffle/chamber/muffler/etc will result in the engine being down on power. The higher the specific output, the greater the loss.

Andy, you're not imagining the difference- it's very measurable on track or dyno. My engines respond exactly the same way (including my long stroke Bullet)

* This isn't the only reason- multiple factors combine to make a wholistic piece- screw one up and the combination won't perform to its' potential.

Just to clarify the above post, the "tuned exhaust length" is that measurement from the exhaust valve to exhaust tip/open atmosphere. Adding a baffle or any type of restriction into this length changes it, and therefore upsets the tuning of the exhaust.

The actual length MEASUREMENT is critical to get right for maximum performance, varies depending on the engine, and has a narrow window in which it can be correct in.

In the case of in an intake tract, the tuned length is open atmosphere/aircleaner to intake valve.

Thanks for all the comments as "Blown" said, the difference is real.

I have a "test hill" that regularly ride and did 4 runs last week, 2 with, and 2 without baffles.

I made sure there was a gap in the traffic so that I would not be hindered, you could certainly feel the difference between baffles / no baffles, I found myself braking on some corners as I was carrying more speed than riding with baffles.

The baffle I was using is absolutley minimal, but you can feel the difference in your seat of the pants dyno - not very scientific but it can be felt. It would be interesting to run it on a dyno.

In the meantime, I shall continue riding with my ear plugs in and try as much as possible to show consideration for others, it just runs so sweetly without the baffles it is shame to stifle it.

Should I get stopped by the long arm of the law, then hopefully the "it just blew out" excuse will work, the baffle will also be used at MOT time.

Exhaust as mentioned by Adrian, I have a short Indian made silencer you can have for a tenner if you collect; I am on the south coast though

The £10 is really just to cover the baffle I bought for it. Just bought a new silencer from our host.


John