Muffler Tech?

[mishaparem]

Originally Posted by Salsa

Does anybody know the limits of aluminum for mufflers. Maybe you could use aluminum on the outside and steel on the inside.

Don

My answer is based on material science theory (how I expect the material to act based on the properties of the materials) not hands on knowledge or experience (I've never built custom exhaust, nor have I seen aluminum exhaust).

The material you can use is a function of temperature and thickness of the pipe. Most bikes should be safe to use aluminum exhaust, but I'd still run a foot or two of stainless first. Aluminum does conduct heat well, so you can theoretically attach aluminum heat sinks to the steel exhaust to reduce the amount of steel pipe you use for the exhaust by cooling the exhaust faster and allowing you to use aluminum earlier, not sure if this would be a weight saver or not. Aluminum is a material is lighter as I'm sure everyone knows, but it also conducts heat much better, so you may be looking at much hotter exhaust burns (pipes may or may not be hotter, but they'll conduct more head into your leg in the same amount of time). Aluminum also deflects easier than steel, so you might be looking at louder pipes with a slightly throatier sound (the high/low pressure waves will expand/contract aluminum pipes more than steel pipes). As a result of more deflection, the aluminum exhaust may not hold up as long around bad welds, if I'm not mistaken, aluminum fatigues faster, bad welds will fatigue even faster.

Using aluminum on the outside of the cherry bombs would probably do a better job muffling sounds than a steel can because the can itself can deflect a little.

Take care not to run the aluminum exhaust too early (before the exhaust has cooled sufficiently), and don't weld the cherry bomb earlier than the exhaust has cooled before the melting point of your packing material. A friend of mine had to buy two complete exhaust systems consecutively for his tuned up bmw m3 because he burned through the cat, and one of the welds on his stainless steel exhaust - pipe walls were too thin, cat was welded in too early.

Generally aluminum sounds like the way to go because of it's deflection, the more the pipe walls deflect, the more energy they take from the exhaust stream. i'm surprised more people don't buy aftermarket aluminum exhaust, but maybe there's something I'm missing. Perhaps it's the cost factor, good aluminum welds are hard to do right, so I assume the people who can make those welds have expensive labor costs.

[ktmklx]

Kelly, not sure if you saw this in my thread or not, so I'll throw it up here. This is a home built flow through muffler using perf tube and fiberglass packing. Perf tube and fiberglass are very common in aftermarket MC mufflers.

There are a few knobs you can turn to adjust noise/power levels.

Length of muffler, longer = quieter
Diameter of muffler, more insulation can be rolled into a larger can making it quieter
Diameter of perf tube, the smaller diameter the perf tube the quieter, usually smaller here means more back pressure and less power
length of perf - more perf length will do 2 things increase perf area and increase back pressure, both will reduce sound.



Here are all the parts for the muffler. The are 2 machined aluminum end caps, 3 weldments, a couple o-rings, a spark arrestor, a bunch of screws, insulation, perf tubing and some aluminum tubing.

[larryboy]

2001 1150GS, the cat is a muffler, it's down low and is a bolt on...wham bam, done.

$95, spend time and effort on something else.

http://www.beemerboneyard.com/18127673648.html


If you're super determined to build your own muffler get a SuperTrapp kit from SummitRacing and build one. You can tune it, it's cheap and made from steel, find a steel muffler, gut it and weld the Supertrapp end on it. Don't overthink the thing, it's just a pipe that lets exhaust out.

[kellymac530]

So after reading everyones ideas, reading posted articles, measuring, and shopping around for parts and pieces I found a set of Ducati ST4 mufflers on ebay

http://www.ebay.com/itm/321075154681...84.m1423.l2649

I figured that if nothing else, the SS piping, aluminum outer tubing, and inner perforated mesh is worth about the $80 they cost.

I plan on trying just one muffler on there to see the volume and then decide if I need to cut them up and use the parts to make a splt dual stacked muffler, or a longer muffler with a bend in it.

Larryboy suggested using a stock GS muffler. I would just as soon use my stock RT muffler. Its free and just as heavy and wide.

I want to lighten the bike as much as possible and then I also want to get it as narrow as possible. I am going to make my own panniers keep them a bit narrower than most. To maximize useable space I plan on tucking the muffler up and as tight in to the rear wheel. It seems like I can use these Ducati mufflers and be no wider on the left than the swingarm is on the right so I may not need a notch in the left box.

As far as time...I am still on doctors orders not to ride, probably july until i am cleared to ride, so I have time and I am cleared to tinker in the shop as long as I take it easy and under 30 lbs. So building my own muffler is something I CAN do to keep my mind occupied and get off the couch for an hour or 2 per day while I heal...good for my soul thing.

Besides, if you are going to cut a bike in half, weld up a different frame, custom brakes, suspension, seat, tank, lighting...you can NOT just bolt on a stock muffler...can you?

[larryboy]

Originally Posted by kellymac530

Larryboy suggested using a stock GS muffler. I would just as soon use my stock RT muffler. Its free and just as heavy and wide.

I don't think you understand what I said, you must be stir crazy.


The cat is the muffler, I threw 17 pounds of muffler away that isn't needed, then I could mount the left side box as close to the bike as the right side box.

Look closely, no muffler other than the cat box down low, even the tip is angled in a way that we never smell exhaust:

[kellymac530]

Got it now...I am stir crazy...but I have been just crazy for a long time now and I have the perscriptions and doctors note to prove it...

On top of just being crazy...I have been just riding the couch for 3 months now...my head is about to explode.

I had not thought about just running a cat. How loud would you say it is compared to a full stock muffler?

[larryboy]

Originally Posted by kellymac530

Got it now...I am stir crazy...but I have been just crazy for a long time now and I have the perscriptions and doctors note to prove it...

On top of just being crazy...I have been just riding the couch for 3 months now...my head is about to explode.

I had not thought about just running a cat. How loud would you say it is compared to a full stock muffler?

Maybe 4 decibals louder than through the muffler.

I'll shoot a video for you later today and post it here.


Here you go:

[kellymac530]

Wow that is really good. Thanks for that.
As Arte Johnson would say....Veeerrrryyy Interestink

[larryboy]

Originally Posted by kellymac530

Wow that is really good. Thanks for that.
As Arte Johnson would say....Veeerrrryyy Interestink

Very common mod, I'm not THAT into BMW's...I think it was only a couple of years of the GS that you could toss the muffler and it was still quiet. I'm sure somebody else knows more than me about that, but my 2001 is one of them.

[kellymac530]

I am trying to salvage as many parts off of my R1100RT and recoup some of my custom parts cost by selling them. The muffler and cat are one thing I think I can sell for more than I paid for the Ducati ones I bought, but If the Ducs don't get me where I want on volume, performance and sound then I will use the Rt and cut off the muffler and make a custom end for it.

Great heads up on this option though, thanks.