MAC 4-1 wrapped the baffle.

Hey guys, I got some aluminum screen and supertrapp muffler repack matte. She's nice and quiet now, and has WAY more torque, but, if I get her up to 5k and really open the throttle, it seems like it looses a couple cylinders.

I'm assuming, when I wrapped it, I've not given it enough space in the muffler to expell all that exhaust gas when it's opened right up. (Too much back pressure) Would that sound about right?

Also, I can definitely hear a distinct sound coming from what seems like the front of the engine, possibly where the headers attach. I can only describe it as an engine under heavy load. It never made a sound like that without the matte material around the baffle. So I'm guessing it has to do with the back pressure as well.

Thoughts?

Thanks all!

 

i think you've got the right idea but how to fix it is another story.
i had a mac with nothing in the muffler and got tired of trying to jet the carb to the muffler so i bought a super trapp muffler and problem solved.

 

Buying a new muffler isn't in the finances at the moment :/. I can just pull the baffle back out and adjust to give it more flow, not today tho lol.

Hope it doesn't louden it any, it's sooooo nice and quiet now.

 

This is the stock innards.

http://i21.photobucket.com/albums/b265/ ... G_0806.jpg

You can see how making that screen too tight would choke it. Basically the only space from in pipe to out pipe, is the space between the pipes

 

So I took half the packing material out and tried it again yesterday. Still too much back pressure. I took all the packing out today, but left the screen in. We'll see how it runs.

Sucks that it won't be nice and quiet, but I'd rather have an engine that revs to 10k properly lol.

 

I have that exact same muffler, and I not only wrapped the "core" I also made another "glasspack" in front of it by wrapping expanded metal drywall mesh and fiberglass mat around a shovel handle.

I didn't take pics, but It was really quiet at first, then as the packing settled-in it started to have a nice note. While riding you hear just the engine.

 

Yep, it was nice to just hear the engine, and not the exhaust. How did you possibly stuff that much into the stock baffle and have enough room for 4 wide open cylinders to breathe out?

 

My previous Seca 900 had a Kerker exhaust.
Inside there is a venturi - (2 funnels together) so small that I couldn't stick my thumb thru. I made my front baffle larger than that.

 

Ahh so it wasn't the stupid offset/overlap MAC design. That's what makes it neer impossible to add packing to this muffler.

The drive in today with no packing was fine to rev all the way to 10k. Guess i'll just have to live with the loud till the MAC rusts out and I have to buy a new can.

 

read your plugs in a few days

 

Oddly enough, the packing didn't change my mix much, I did colortune with full pack, half pack, and it was the same colouration. I will check with colortune this weekend again tho, and check the sync again as well.

 

colortune isn't going to tell you what the 4/1 did. at idle there is such a small volume of exhaust compared to mid range and wide open where he pipe comes into play

 

What "new can" is available? I thought MAC's were about it for XJ exhaust systems these days.

 

I'm sure i can get some kind of supertrapp that would fit the same header.

That's more what I meant.

And that's very true Polock I've run it stock for years, so it shouldn't be much different than before.

 

More muffler tech and research than you'll ever need at this link - -

http://naca.central.cranfield.ac.uk/rep ... t-1192.pdf

 

Daaaaamn, that's a lot of info lol

 

Along the same lines, has anyone made, or tried to make a long straight flow chamber that can be wrapped like a conventional bike muffler?

 

My "unique" muffler design won't fit on a bike, but under a car/truck.
The exhaust goes down a straight tube into a "P" shaped pipe that is in a box. Sound is reflected off the top "dead end" back to the engine, and the sound waves endlessly travel around the circle of the "P" The inside of the circle has the holes, or louvers and vents into the box, which is lined with fiberglass. Eventually the exhaust exits the center of the circle thru a pipe.

It would take alot of welding, but it seems the sound waves would get chopped-up, dissipated, and absorbed.

 

The "Swiss" muffler for European ultralights.
Easy to fabricate, light weight.

http://www.piteraq.dk/flight/muffler.html

 

Just something to think about: the original stock Yamaha mufflers that came on our bikes accomplish the whole thing without the use of any sort of "packing." There is nothing inside but a series of baffles, plates, tubes and holes. Much of what went into their designs is specifically covered in the NACA study.

BTW, for those of you unfamiliar, NACA (1915 - 1958) became what we now know as NASA.

(Maybe this IS Rocket Science, after all?)