WR426 and DRZ-E Sound testing completed.

I finally did the sound testing on my DRZ-E and my Son's WR426. I tested both bikes 3 ways.

1. Pure stock

2. Custom made exhaust cap

3. Exhaust restrictor (cap) removed.

All testing was done with a Radio Shack analog meter set to "A" weighting, 20" away at a 45 degree angle. The 1/4 trottle setting is just an estimate but all testing was done at the same setting.

Lets talk about the DRZ first. The custom cap consisted of a plate with a piece of 1.5" i.d. thin wall tubing 2" long welded to it. The spark arrestor is stainless steel screen welded to the inside. The air box snorkle was removed and jetting richened up.

Stock at idle = 84 db

Stock at 1/4 throtle = 96db

Custom cap at idle = 85 db

Custom cap at 1/4 throtle = 96db

Stock cap removed at idle = 93db

Stock cap removed at 1/4 = 102db

The WR426 gave very interseting results. The custom cap (actually an insert) is a plug with a 3/4 inch hole drilled thru and retained by the stock restrictor screw. Stock jetting and stock air box.

Stock at idle = 83 db

Stock at 1/4 throtle = 116 db

Custom insert at idle = 85 db

Custom insert at 1/4 throtle = 110 db

Stock restrictor removed = 92 db

Stock restrictor removed at 1/4 throtle = 116

I can't understand why the stock insert and no insert gave the same reading. They have a different sound, but the little stock insert is very loud in a different way. I suspect that the frequencies are different to our ears but the meter can't tell the difference? Tests were run several times to make sure of the results.

Any way, that's what I did. Any suggestions or comments are greatly appreciated. I will post this at the Yamaha site and on DRN as well.

I'm not sure if it's the way you held the meter in relation to the exhaust or if it's the meter itself but your decibel readings seem way high for the Yamaha and about right for the Suzuki. If I remember correctly Dirt Rider did a test many months ago on open exhaust systems for a CRF450 and the loudest they came up with was something in the 108-110db range. I don't think stock uncorked Yamaha exhaust is anywhere near 116db, at least the way the Rangers do the test. I run the FMF powerbomb and Q-pipe and was sound tested at 95db. Eric


To be sure of your readings you need to use a tachometer and hold the revs at 4500 rpm for the WR and basicly the same for the DR, although I ought to look up the proper rpm for that bike model. The WR should test much quieter, definitely sub 100 dBA with stock pipe but should be just over 100 dB with the insert removed. The results are very sensitive to rpm as you saw from idle vs your estimated 1/4 throttle (revved a bit) speed. On the WR you'll get the loud result with the SA in and the insert out, no need to pull the SA too. All your idle readings look correct.

When I had ranger Rick sound check mine, it was way lower than 1/4 throttle. Hardly twisted the throttle until the wire RPM tester started going around in circles. My guess is that the Yamaha revs higher at 1/4 turn than the Suzuki.

Ok, I looked it up. It's 4000 rpm (testing rpm) for the DRZ400E engine prefixes k416/k417 and the little wire was a resonant sirometer that did what you saw when it got the right frequency vibration off the bike, i.e. ranger Rick set the specfied rpm into the thingy just before he tested your bike and used it as a portable tachometer.

Try to purge this 1/4 or "part" throttle concept as being a component of the test. It's purely rpm based.

For reference it is 4500 rpm for 98-00 YZ/WR400/426 models. 01/02 WR426 is 4250 rpm, 01/02 YZ426 is 4500 rpm, 01/02 WR250F is 6500 rpm, 01/02 YZ250F is 5250 rpm (I think there was a publishing error on the 250 values - reversed). The 03 values aren't published yet. The 01/02 DRZ400E are still 4000 rpm and the DRS400S's are all 3750 rpm (as if they need testing!).

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