White Brothers E-Series Exhaust ?

Just picked up a 99 WR400 with YZ timing and carb mods. Got checked today by the USFS, Exhaust too loud, 105db, limit 96db. It has 10 disc's including the closed end disc.The bike seems a little lean, will removing disc's quiet it up, and how many? Thanks :)

Good luck. The E-Series comes in two types, the S bend and the ProMeg. Yours sounds like the ProMeg. Max disc count is 18, the minimum is four, and it sounds like you're running nine. The closed end disc is the spark arrester. The Promeg by design is a maximum horsepower "race" pipe and is very loud. I have a ProMeg on a four stroke quad with a quiet core insert ($40 from White Bros.) and 7 discs and it reads about 93 dB(A) at 4000 RPM's. The quiet core really chokes exhaust flow down as it quiets it and is said to be good for a 6 dB reduction. As far as reaching 96dB without the quiet core, I don't think you'll be able to do it. You can take it down to four discs but you'll have to rejet and I would expect the power to be down quite a bit. I would ditch your pipe and buy something legal. Because of the sound issues, I will never buy another one. Here in MI our limit is 94 dB, which is almost half again quieter than your limit.

(A 3 dB increase in sound is TWICE as loud. Sound Pressure Level (SPL) is not linear.)

It's the S-bend. Put the stock exhaust back on? The person I got the bike from did all the mods prior to the exhaust. Runs a little lean with the exhaust...Thanks

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