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rwhitlock

Quiet exhaust for the YZ426

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I ride with 2 buddies. One has the YZ426 and the other has the DRZ400. The YZ kills the DRZ by the way (as if you couldn't have guessed..).

However, that YZ is sooooooo damn loud!! I am getting a new bike in the spring (leaning towards the WR or the YZ 426.

Does anyone know what the stock decibel level is?? Also, are there any aftermarket exhausts that quiet the bike down? I don't motocross, but rather agressive mountain riding and can't stand the loud noise.

Oh, the good thing about the DRZ is that it is quiet... :-)

Thanks!

Rod

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we meet again!

have a look at the archives on the WR site. go back about 60-90 days or put in 'stroker exhaust ' in the search box.

clarke has quiet & quick pipe. by combining the powerbomb header & the stroker taipipe (c/w spark arrester).

Taffy

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Taffy, Do you know what kind of jetting changes would be required with that combo? I here Stroker sends all new items for this with their S/A but that is for running the stock header. What does the power bomb add to the equation? From what I've read, the

Stroker S/A makes the 426 VERY smooth down

low. Enough to almost make it ridable on tight trails. How much do you think would be given up on the track? Thanks in advance.

dirtdad

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I run a corked up WR400 pipe on my YZ426 for compatibility-with-humans riding situations. It bolts right on. It's about as quiet as a DRZ400 in that form. The dB change is immense. The power is mellowed a bit on top (as expected from the high rev extra back pressure). You have to rejet a bit, I went one main leaner and dropped the needle one clip. Runs just fine and wheelies and roosts on demand.

I suspect the U.S. 01 WR426 will have the pipe already, with removable insert (which when removed makes it pretty much exactly as loud as the YZ - I measured them both) and will have trail friendly transmission ratios vs the YZ. However, the WR probably won't have the suspension adjustability of the YZ. Unless they change the rear shock for 01. There's always some tradeoff. Another big issue is the rock hard but agile to ride on YZ seat/tank vs the wider, guppy WR tank. There's plenty of discussion of that here.

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Dirtdat

Jetting as follows:

PJ = 48

Fuel screw at 3/4 to 1.5 turns out

DVP needle fifth clip position from the top

178 to 180 MJ

DVP needle is Yamaha part # 5BE-14916-DP

Make sure the needle has DVP stamped on it in the last three letters

I have a 99 WR 400 with YZ cam timing and it is puched out to a 420 running a 13.5 to 1 Weisco piston.

Clark

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Pro Circuit has recently offered a quiet core for their T-4 system, so you can run it one of three ways:

1. Open (loud)

2. With the screen insert (still loud)

3. With the quiet core/screen combo (29.95 extra). I've inquired PC about the quiet core, because I'm planning to try enduros and some (all?) have noise restrictions. They claim the quiet core will give a decible reading of under 92. I imagine it would hurt top end power a bit, and possibly require compromise jetting, to work with or without the quiet core.

You have to buy the entire system (header and silencer) with the T-4.

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By corked up I mean it has the little insert still installed. Without the insert, the outlet is about 1 1/4" dia. and it's super loud. No, there's no packing in the WR400 muffler, just baffles. I'd say it scores low 90's dB and would pretty much be about the same as option 3 of Holeshot 's posting, except maybe it weighs more than the Pro Circuit T4 system. The screen always stays in the WR400 pipe, unless you take off the entire rear plate! If a guy goes that far, might as well put the YZ pipe on - no screen, loud, high revving low restriction, run bigger jets again, lightweight and change the packing every so often.

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