Re-packing aftermarket mufflers

[scooter2131]

We are, or should I say were, running a Yoshimura RS-3 muffler on our f4i this year until I tested for noise today. We're sitting up around 119-120dB at 11k. Has anyone ever re-packed this muffler or any aftermarket mufflers? Is it worth it? If so what is the best packing to use?

[Jay Fleming]

I dont know the best packing to use, but I know it's not that hard. I don't know the specific muffler you're talkin about, but I'm assuming taking the end cap off is only a matter of a few bolts, so it's real easy. But you should be able to go to any motorcycle parts store and get whatever they have. But to actually pack the muffler, take off the end and the packing will pull out with the center tube. Just take the old packing off, rewrap the new packing on as tight as possible and use bailing (or similar solid wire) to wrap the ends of the packing so it won't unravel (sp?). Then just put the packing and tube back in the can and bolt the end back on. Easy as that. Probably 30 mins work, maybe a bit more if the end is riveted on.

[Daves]

We are also using a Yoshimura muffler. In order to repack it, I believe the rivets must be removed and the end must be taken off. However, we have noticed a +/- 10 db difference with our decibel meter compared to the SAE judges'. Instead of repacking, we are going to take custom baffles to competition with us. They fit on the end of the muffler and are of various designs.

[scooter2131]

I was talking to my buddy last night and we decided we'd try out some baffles before we tore the muffler apart. Have you tested your baffles? Are they keeping you leagal w/o killing power?

[Handles]

i wouldnt think that repacking would allow you to drop 10db, after having a lot of trial and error last minute experience and a couple of comps!!!
the major problem i have found is the noise from all the other sources in the engine bay, ensure that your muffler exit is as far back as possible in order to isolate the exhaust noise, i know you can save many valuable dbs by addressing this
good luck with it http://fsae.com/groupee_common/emoticons/icon_wink.gif

[Andycostin]

Baffling will kill power by creating resistance and therefore backpressure, unless it is done so that it doesn't restrict the flow, eg. by creating separate compartments on the outerside of the straight through pipe. This works in an acoustic way, but will prob be difficult to drop more than 10dB.
You'll also have trouble dropping 10dB with packing, we managed 2 or so last year, and could've probably got more, but didn't need it.
Cam Angles and Timing can have an effect on it too, but I guess you're probably well past being able to do that, and it may cost you power or increase exhaust noise.

Good luck

[scooter2131]

Turns out Yoshimura sells a low-volume insert for about $20 and should lower the volume about 8dB. I'll follow up w/ actual results this weekend.

[Agent4573]

Scooter, we had to run a baffle last year in a last ditch effort to get us below sound. We came in 10th in acceleration and like 14th in autocross with the baffle in place so it didn't hurt the power that much, we just needed more suspension tuning. The baffle I made dropped us 6 decibals on our sound tester...

[Jay Fleming]

What would a baffle look like to fit this type of application? Is it basically a flap or something inside the exhaust?

[Daves]

http://images.google.com/images?q=tbn:yPGkjpAaJp8J:www.yoshimura-rd.com/products_images/teckit.jpg

[scooter2131]

Hey everyone,

Sorry my reply took so long, but I'm sure you can all attest to many things slipping your mind in the wake of FSAE. We only dropped 6dB with the Yoshimura insert. Thanks to a forgiving inspector at noise test, we read 109.8 dB when the measurement was taken outside the rear wheel.

During the awards banquet there was mention of changes to be made with regards to the noise testing of production engines (or something along that line). Does anyone remember more specifically what was mentioned and/or care to speculate as to what rule changes we might see for next year?

[MikeWaggoner at UW]

I think that was mainly affecting industrial engines. So if you're racing a John Deer, or doing something strange with a Briggs, you're ok.

[Engine Dude]

Hey Guys,

Did you guys source your Yoshimura's from a wrecker or did you get it new?

Has anyone approached them for sponsorship?

Thanks

Sam

[scooter2131]

We bought our Yoshi new from Yoshimura-RD in Cali. They offer a discount to all FSAE teams; I believe on the order of 25%. I'd tell you who to contact, but in the past year I think at least two guys have left the technical sales department. The last guy I talked to was Aaron Austin if that's any help. I've not approached them as a sponsor for a couple reasons: They already offer a good discount and I don't know many teams that run their products w/o trying to modify them to pass noise test.

Anyway, their website is
http://www.yoshimura-rd.com

Hope this helps and good luck.

[CMURacing - Prometheus]

i believe cal poly pomona has had them as a sponsor in past years, but they're neighbors...

[Bubba]

Hey Scooter, this year we ran the Yosh model with "Zyclone" baffles and we passed at 106db with our 2003 F4i. After getting pretty well beat down in the last 2 competitions because of sound, we played it safe this year. I wouldn't recommend getting one from the scrapyard though. We noticed the Yosh get much louder and raspier just through a couple weeks of testing with it.

*Edit- We did NOT modify anything other than chop off the 2 feet of plumbing that came with it.

[Bryan Hagenauer]

http://www.csupomona.edu/~bjhagenauer/CalPolyPom-01.JPG

Yes, Yosh R&D and the Yoshimura Suzuki team are just a few minutes away from us, and we've had a few alumni work there.

EDIT: in 04, right before comp Yosh repacked our TRS muffler for us, we only passed noise by a few tenths.