Sports Mufflers

[Ross]

Did this today up the Old Pacific Highway. I just slung my camera over my back. Plus it picked up some wind noise too. Should not have had baked beans....

This is what my staintunes sound like with panniers fitted as these do alter the noise etc.

http://www.youtube.com/watch?v=Br68K6gacnw

[mattcfish]

Any buddy try any of "Flat Racer's" mufflers. It's a good selection of after market megaphones.
http://flatracer.com/#/exhausts/4537795367

[jjwithers]

While we are on the topic of mufflers, i am thinking of adapting a set of mufflers to a /5 engine from an old BMW R12 (from the 40s). It will be more of a stylistic decision vs anything else.
Will the difference of back pressure be a cause for problems when it comes to tuning a /5 motorcycle with pipes meant for a smaller engine?
I can see it adversely affecting the horsepower a bit...?

Thanks

-josh

[Motorhead]

Keep the Balance tube so even a little higher back pressure won't hurt if you jet right

besides a earlier muffer can have less back pressure depending whats inside so I'd be suprized if it did have more

[jjwithers]

Keep the Balance tube so even a little higher back pressure won't hurt if you jet right

besides a earlier muffer can have less back pressure depending whats inside so I'd be suprized if it did have more

I didn't think an earlier muffler would have more back pressure. I'd guess less because of a smaller engine...
But what is a Balance tube?

[Motorhead]

Are you kidding me? Look at your Cafe exhaust headers, the balance tube is what connects both sides most are in the front like your cafe, later years back farther between the tranny some front and back

I recently went to a 17" taper from a Harley with a Mac header with balance tube.......... the motor responce is Crisp

[jjwithers]

AAh, the crossover pipe. I've never heard of it being called a balance tube.

[vanzen]

While we are on the topic of mufflers, i am thinking of adapting a set of mufflers to a /5 engine from an old BMW R12 (from the 40s). It will be more of a stylistic decision vs anything else.
Will the difference of back pressure be a cause for problems when it comes to tuning a /5 motorcycle with pipes meant for a smaller engine?
I can see it adversely affecting the horsepower a bit...?

Thanks

-josh

Theoretically, given that the ports and pipes match, and all else being equal,
a smaller diameter pipe (within defined practical limits) will increase exhaust velocity,
the engine will begin producing more torque at a lower RPM,
and the torque peak RPM may be lowered somewhat.
Conversely (as torque and HP delivery are related) HP, or rather, top end speed may suffer
by virtue of the volume of gasses exceeding the capability of the pipe to carry them
and the possible adverse effects this situation will have upon exhaust scavenging.

These statements grossly oversimplify a very complex situation
and should not be considered as a replacement for testing –
Exhaust system changes need to be carefully calculated
and then objectively quantified with comparative dyno testing.

The term "Back-pressure" will frequently be misunderstood in any real productive / performance sense.

The "Crossover pipe" is intended primarily to modify the torque delivery curve and torque peak delivery RPM,
i.e. provide more torque at a lower RPM to enhance drivability,
and place the torque peak at a reasonable and usable RPM for street driving.
Later dual-crossovers were added with essentially the same intentions
and with the purpose of compensating for other engine changes (necessary to satisfy the EPA)
while retaining consumer performance expectations.

A piece of hose connected between the vacuum ports on the intakes
will do an effective job of "balancing" (vacuum) differences between cylinders.

[Ken in Oklahoma]

A piece of hose connected between the vacuum ports on the intakes
will do an effective job of "balancing" (vacuum) differences between cylinders.

Can you elaborate a bit vanzen? I'm familiar with the balance tubes found between the twin carbs of a British vertical twin, and I believe that I understand why and how a balance tube works. And I certainly noticed the absence of a balance tube on my first airhead.

My guess for the reason why airheads don't ever have a single carb (with long tubes feeding the cylinders) is that the tubes are too cool and would have a tendency to de-atomize the fuel from the fuel air mix; and also that the atomized fuel, even at higher temperatures, would still have a tendency to wet the intake runners and alter the mix. The effect would be (at least) to make the engines much more temperature sensitive.

If I thought about it much at all, I thought that a carb to carb/intake manifold balance tube would cause similar problems due to the fuel in the fuel air mix dropping out of suspension and upsetting the mixture. This would especially be the case of unbalanced carbs where, instead of shuttling back and forth, the balancing fuel/air mix would have a net flow from one side to the other.

Or, to pose my question in many fewer words, why do you suppose BMW didn't do it?


Ken

[vanzen]

My thought will be that BMW didn't need to add the vacuum intake balance hose -
My experience is that a hose thusly connected does help to equalize vacuum signals between cylinders
and ease the task of tuning & balancing the carbs ...
even as the benefits may not be readily apparent or, for that matter, even significant
... until headers without a cross-over are fitted.

... even as that function of the cross-over
still cannot be considered it's primary reason to exist.

It's a tiny hose after all:
I do not "see" fuel-mix traveling between intakes / heads / cylinders -
so much as a moderation of the vacuum / pressure signals to instruct the carbs' jets on how to behave.

Unbalanced carbs are destined to cause any engine to run like CRAP.

I once installed a single 2-barrel Holley to power a Gold Wing –
talk about long intakes ... it ran very well ... as do many single carb auto engines.
Witness the VW flat-4 fitted with a single 1-barrel Solex.
Having said that, the intake path on a BMW flat-twin would be long and, perhaps, fairly convoluted ...
and without ever having tried such a thing ...

And bless Jim Crey for introducing a perforated straight tube glass pack in a BMW can onto the market ...
although the first recorded instance of the use of such a "gutted can" may have been in 1976 - on old #83.