Super-quiet muffler to shut-up Yamaha 450

[Charles Kaneb]

Last year, we unsuccessfully tried several GYT-R and FMF mufflers to try to make our Yamaha 450 single pass sound.

None of them worked. We ended up using a stock YFZ450R "Forest Service ATV" muffler, which weighs almost 10 lbs by itself, and barely passed sound at 108 dB at competition.

The 2013 car's structure and shielding may be even louder. Even the "Forest Service" muffler may not pass sound this time.

I've seen many cars over the past few years pass sound with little, light mufflers on singles. Even the big-wing teams with lots of opportunities for sound reflection appear to get away with it.

Is there a COTS muffler that's really, really quiet? We can stand to give up several horsepower to restriction, but I don't want to have a muffler that appears to have come off of a Cadillac Eldorado (because it did) mounted on our smallest, lightest car yet.

[Drew Price]

When I was competing we put a new-ish stock Yamaha R1 muffler on the Suzuki LT-R450. They have a titanium case and header pipe and are very light, and pretty light, ~3 lbs if I remember right.

We got them for free from a motorcycle mechanic who swapped out for some Yoshi's, and they were light and quiet enough. And the price was right, of course.

These ones, currently on eBay for $40 for the pair. This ad says '04-'06, not sure if this series was used more or not, but this is what they looked like.

http://www.ebay.com/itm/YAMAHA...em257cf1cc15&vxp=mtr

[Mbirt]

108 dB with the plugged-up stock muffler (.5" outlet)? That's pretty astonishing. We've had a quiet single using a stock baffled streetbike muffler like Drew mentioned. It was a mid-2000's R6 muffler with an aluminum shell.

You need to attenuate other noise sources if last year's car blew 108 with a peashooter. We were 105 at MIS last year with a straight-through absorptive muffler with 1.5" OD tailpipe on a WR450. There was a team running a single and an aluminum monocoque that tested astonishingly high at MIS in 2011, close to 130 dBA IIRC. They diagnosed a resonance issue in one of the large, flat surfaces of the monocoque and then passed sound. Then there was GFR's long tailpipe extension at West in 2011 to route the microphone away from their diffuser and pass noise.

It's worth investigating what could be resonating at 7000 rpm on your car.

[Racer-X]

Like others have said you might want to try a baffled muffler or putting the spark arrestor/silencer insert back in your FMF.

If that doesn't do it you have something else on the car making that noise, or a crazy tune...

[Charlie]

Something else is your primary noise source. What type of intake do you run? How is it oriented?

[coleasterling]

It was nowhere close to 108 with the stock muffler. I don't remember what it was at Lincoln, but we were testing around 103 and were often lower than that.

The stock YFZ450 muffler is, in fact, a fully baffled steel behemoth, but it works REALLY well. In this case, the after market mufflers we tried were right on the edge or just over with the quiet insert, so we decided not to risk it and gained some more rear weight bias.

Charlie, the intake was oriented up with the filter fitting just under the top of the roll hoop and the restrictor and plenum in-line. It was made of aluminum and quite stout. I have serious doubts about it resonating significantly.

[Mbirt]

Originally posted by coleasterling:
I was on that team and it was nowhere close to 108 with the stock muffler. I don't remember what it was at Lincoln, but we were testing around 103 and were often lower than that.

The stock YFZ450 muffler is, in fact, a fully baffled steel behemoth, but it works REALLY well. In this case, the after market mufflers we tried were right on the edge or just over with the quiet insert, so we decided not to risk it and gained some more rear weight bias.

Charlie, the intake was oriented up with the filter fitting just under the top of the roll hoop and the restrictor and plenum in-line. It was made of aluminum and quite stout. I have serious doubts about it resonating significantly.

-Cole

These noise levels make more sense. In this case, the fmf muffler and quiet core in conjunction a 90 deg elbow tailpipe routing the noise vertical and away from the microphone should pass.

[Charles Kaneb]

Originally posted by coleasterling:
I was on that team and it was nowhere close to 108 with the stock muffler. I don't remember what it was at Lincoln, but we were testing around 103 and were often lower than that.

The stock YFZ450 muffler is, in fact, a fully baffled steel behemoth, but it works REALLY well. In this case, the after market mufflers we tried were right on the edge or just over with the quiet insert, so we decided not to risk it and gained some more rear weight bias.

Charlie, the intake was oriented up with the filter fitting just under the top of the roll hoop and the restrictor and plenum in-line. It was made of aluminum and quite stout. I have serious doubts about it resonating significantly.

-Cole

Cole - we'll have the sound meter calibrated fairly soon and as soon as -12 runs again I'll retest. It's got a fuel pressure problem. I remember the car coming surprisingly close to the noise limit even when we could barely hear the exhaust.

[Dunk Mckay]

We recently moved from making our own carbon housing ones which barely got us passed scrute, to using a titanium akrapovic. Dropped our average from 108/109 to 103.

We run an R6 and have done for a long while now. But there is a smaller akro silencer lying around. Not 100% sure why but we did used to run a 450, could have been for that. Whether it was effective or not is another question. But the bigger one we use now is good.