Motorcycle muffler mods to reduce noise
 

Hi all,

I've been stuffing about for a while building up a Japanese style custom bike, based on an old Honda CB400F.

The muffler was rusted out when I got the bike so I replaced it with a cheapo ebay unit. I think it looks OK but it is REALLY loud.

As you can see from the pics, it has a perforated tube which bolts in to the position I've shown in the third pic.

Assuming I'm not Tim Hancock and only have mere mortal fabbing skills (at best), what would you suggest to bring the noise level down a bit.

http://forums.pelicanparts.com/uploa...1283316312.jpg

http://forums.pelicanparts.com/uploa...1283316322.jpg

http://forums.pelicanparts.com/uploa...1283316331.jpg

http://forums.pelicanparts.com/uploa...1283316339.jpg

http://forums.pelicanparts.com/uploa...1283316348.jpg

that is a pretty cool scoot, how about some baffles, maybe with some fiberglass packed in there.

Throw the whole system away and start over. That header design is among the worst I have ever seen and the "muffler" needs a float test in a pond. It's hard to believe it will even run, looking at that baffle design.

The nifty thing about motorcycles is that it's not all that hard to graft a part from Bike A to Bike B, if you do a little homework. You might even find a new system, or a good used one, for that model of bike. Early Honda fours have a fairly decent following.

JR

Without knowing exactly what the internal structure is, my first thought would be to shove a washer shaped piece of steel or varying lengths of solid steel round stock maybe 2/3 of the way into the perforated tube and see how it sounds. You could use some wire to temporarily hold it in place. If that worked, you could permanently weld it in place.

My guess is that the exhaust dumps into the larger outer section of the muffler, then is forced through the perforated tube and then exits through the short narrow tip. Reducing the area by blocking perforated holes that the gas must pass through should IMO quiet the sound.

In my opinion, it will be an exercise in trial and error as far as performance goes. At this point, I assume you are not too worried about eeking the last ounce of performance from the bike and simply want to quiet it down a bit. (I am in the same situation with my nearly completed cafe project.) It seems exhaust system design is somewhat of a black art and often involves trade-offs relating to where in the powerband the exhaust works best.

My suggestion for quick/easy/affordable: Supertrapp;)

Hey! I posted that last night but it is gone!!?? Hahahaaa. I wasn't even drinking!
Danny Ocean suggested steel wool. OP said he tried it and if tight it choked out the engine and if loose it did nothing. I agree with Java and Roux, start over. With salvaged parts you could get out less than 200, even if you bought a brand new supertrapp.

"My guess is that the exhaust dumps into the larger outer section of the muffler, then is forced through the perforated tube and then exits through the short narrow tip. Reducing the area by blocking perforated holes that the gas must pass through should IMO quiet the sound."

That's right Tim, the muffler is otherwise empty aside from the perf tube. However, I can't wrap the tube as it pushes in, with a light interfence fit, from the muffler outlet.

I'll try blocking a bunch of the holes with an internal sleeve.

I thought of Supertrapps but they seem hard to come by here (Australia).

Wrap course steel wool or muffler fiberglass packing around that perforated sleeve and it'll quiet it down a lot. Or spend a bunch of money like others suggest. Up to you ;)

It's good that you are trying to quiet it down. You know what they call guys with loud obnoxious bikes nowadays, right?
They even changed the definition in the dictionary. I saw it on TV!

Lets see more pic's of the bike :)

put a turbo on it