Final results - Sound - 01 WR426

"Q" series pipe, power bomb (stainless) header, repacked loosely with MSR silent sport packing. 94.5 db at 4250 rpm. 20 minutes prior with same setup except repacked tightly with FMFs 4-stroke packing - 97.8db. All same parameters with original packing - 96.6 db. Same place, roughly same conditions. Guess I don't need that KTM after all, I can't afford it anyway.


Now, here's a guy who knows how to get meaningful data! Thanks, Tom, for the info. I knew it was pretty quiet compared to that empty Powercore 4SA! Sounds like I may have a chance at passing after all.


Absolutely you can pass and we have the loudest bikes on the planet. Really, my aim was to go as quiet as possible and still have a shred of performance. I have data from the stock pipe as well from the same location - 88db with insert 104db w/o.

My friend has a 2001 YZ426 that tested at 94.5 db as well with a brand new "q" and stock header. Just for info new 426 and 450 yz's were not passing with the pro-moto billet endcap and diffuser. I thought that was pretty interesting. Anyway , we also invested in a sound meter, a tuning fork for RPM and an "official" copy of the SAE spec sheet.

As someone said before knowledge is power.


Tom, do you know how a stock Canadian pipe compares with your stock US pipe that tested 88 db with the insert?

Tom, is 4250 rpm the level that all WR's are supposed to be checked? Here in Salida Co, the park service is testing at 6000??? I told the guy I thought it was lower, but I wasn't sure. :)

its 4500 for the wr and the yz

I can t find the link and I thnk its posted here on one of the yamaha forums

Thanks for good info. In Michigan they use 4500 RPM. I had some 426's tested stock with stinger, stock w/o stinger and got very similar results to yours. I also did stock pipe with vortip and got 93DB. I am getting setup to do more testing. Question, are you using Radio Shacks analog or digital meter, and if not what are you using. In Michigan rangers us a resonance tachometer that they place upon the transmisson set to vibrate wildly at 4500 rpm. I have searched everywhere for that unit. Do you know anything about this type and is it what you use. If you are using an electronic tach or whatever could you tell me what you use so I can go that route. Thanks

Jim, what are the sound limits in Michigan? CCC rides I think are 94 db, is this CCC or Michigan requirement?

According to the MIC handbook and supplement sheet:

98-00 ALL YZ/WR 4xx 4500RPM

01-02 WR426 4250 RPM

01-02 YZ426 4500 RPM

01-02 WR250F 6500 RPM

01-02 YZ250F 5250 RPM

IIRC the test RPM is based on one half the max horsepower RPM.

More info can be found at the Motorcycle Industry Council website

Ice box I have no idea about the canadian version of the motorcycle.

As for the sound meter it is the radio shack digital meter and we calibrated it with the rangers on the last weekend while we were up there. It is very close to the rangers. (within .01) The tachometer we got from an engine shop, it is the same as the one you mention, it was relatively cheap.

Obviously it is not the same as the rangers but, again, we are close. Make sure you know your RPM, BEFORE you get tested.

Tom Maguire

Do you know anything about this type and is it what you use. If you are using an electronic tach or whatever could you tell me what you use so I can go that route. Thanks


Go to any small engine repair shop. They can order you one from Briggs and Stratton or the like. I paid about $14 for mine.

Thats exactly the one I have.


The sound level for Michigan is 94dB and this is the legal limit for public riding areas (MX tracks not included). The CCC just abides by that limit.

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