Taming the twin pipe Sport muffler..

[Vipergrün]

Well, I love the sound of my AJUSA twin pipe Sport muffler. Is it loud? Yes. Is it obnoxiously loud? Not to me It has that raw, Porsche ralley sound.

Others, however, including my wife said *enough*!

So, on a quest to tame the beast I ended up purchasing some Samson Exhaust 10" baffles from the local Harley shop. I had trim to 9.5" for a good fit. A 1/4" hole is drilled in the exhaust pipe at the muffler end for the set screw.

Made a substantial difference in the raspiness of the original sound, but is still sweet. No obvious loss in power, perhaps a bit more torque on the low end due to increased back pressure, does that sound right?

So, this is a recommended tip for anyone else wanting to tame their sport muffler. BTW, a couple twists of the screw is all it takes to remove them for track use.

Here is a pic. I went with *A*.

[pbs911]

Great idea Brad. I'm actually going to go with the baffles in the pipes exiting the muffler on my Fabspeed set up. Although the sound is great, I am going to see if I can quiet it down just a touch. Can you give % of how much the baffles tamed the sport muffler? Why did you go with A over the other choices?

BTW, I'll bring the tips up to Ingo's for you.

[Vipergrün]

Thanks Paul...

According to the *wife-O-meter*, the sound, both at idle and driving appears to be reduced by about 1/3. Not so much of that Piper Cub sound at idle and that raspy sound at 3K is mellowed out. Kinda like the Prozac affect, just takes the edge off...

I went with that choice based soley on the pipe diameter, it was the only one that would fit. They have a pretty good selection, including a Shortie version which may work well where this is not as much exhaust pipe.

Here is their URL;

http://www.samsonusa.com/samsonhome.html

[Doug Zielke]

I ride H-D, and Samson pipes have a rep for being pretty obnoxious themselves. The baffles they offer probably work better on the AJ muffler than the Samson pipes.

(Message to Jasper....pay attention to this thread. You will be asking me where to get these baffles before long. )

[Randy Webb]

No, increased back pressure will not raise the torque.

Unless you are willing to sacrifice performance for sound, your options are the factory stock muffler and the factory sport muffler.

[jmz]

Are you sure that added back pressure can't produce more torque? I always thought that was the case.

[Vipergrün]

Originally posted by jmz
Are you sure that added back pressure can't produce more torque? I always thought that was the case.

JMZ, that's what I thought as well. I know it's all subjective, but it *feels* a bit stronger at the lower end now. I'm sure a dyno could tell the truth. I am sure of one thing, though, this muffler, with and without baffles gave me an increase in torque and HP throughout the range.

[pbs911]

Brad, I forget, are you running SSI or pre-74 exhaust? I noticed an increase in torque with both.

[Vipergrün]

I'm running set of custom Stainless HE's which I picked up from Mike Z. Definately an improvement adding those, but I think I can feel a subtle difference in the muffler, with and without the baffles.

[Randy Webb]

What makes you think it would increase torque? Consider this: too much back pressure will inhibit evacuation of the exhaust.

Now, it is possible that the superposition of the pressure troughs will change and somehow be more favorable to cylinder filling -- but there is no reason to think that will happen -- it's possible that random hammer blows to the MFI will improve it too...

[campbellcj]

My understanding is that muffler backpressure doesn't add torque, it moves torque up or down the powerband. And if exhaust restriction becomes excessive, impacting exhaust gas velocity and cylinder charge evacuation, then torque & power will decrease significantly.

[David Ceruti]

The discussion on back pressure may be a bit OT for this thread but I have 2 cents to spend.
There may be a bit of a misconception going here from two different understandings of back pressure. The one is increased pressure caused by restrictions in the pipe. Now I can see that putting the silencers in the outlets will probably raise peak pressure in the system and I can't see that this will improve things at all.
Tthe other understanding of back pressure is the pressure waves that are formed in the pipes by the pulses when the exhaust valves open and close. When these pressure pulses hit a change in the pipe, usually at the collector, they reverse back up the pipe. If the headers are the right length the negative pressure wave gets to the Exhaust valves just in time to get more exhaust gas out and the positive wave arrives just as the valve is closing and stuffs any of the fresh mixture that was "leaking" into the exhaust back into the culinder. A well designed pipe will increase power and torque by maximising this effect.
Now adding anything to the end of the system is going to have so little effect on these pressure waves as to be insignificant.
My guess is that the increased torque you felt is just the seat-of-the-pants dynometer being influenced by the lack of talk from the wife-o-meter
Enjoy the (relative) silence
David

[jwetering]

(Message to Jasper....pay attention to this thread. You will be asking me where to get these baffles before long. )

That's funny Doug....I was just thinking about how I'm going to find a set of these here in Vancouver. I especially like the discussion about torgue and back pressure.

This hotrodding is fun!

[Cornpanzer]

Too large of an exhaust can cause a loss of HP. A friend street/strip VW engine went from approx 200 hp to 214hp by putting a smaller collector on the exhaust. The concept as I understand it is that the smaller collector causes a venturie effect which will create a negetive pressure in teh exhaust which helps scavange the gasses. I doubt that this theory would apply to tailpipe inserts however.