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dr_penner

Sound testing XR650R (long)

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Hi everyone,

This post is to relate my experience with sound testing my XR650R. I used a Radio Shack sound level meter which measures decibel output from 50 to 126 dB. I attempted to recreate the USFS test with the device held 20 inches from the exhaust tip at a 45 degree angle to the long axis of the muffler. I was rather surprised with the result.

My understanding of the measured output of the two Honda baffles was that the stock restrictive baffle was 82 dB and that this was to allow Green sticker certification in California. I assume that this was measured in the above fashion with the engine revving to some percentage of maximum. I have heard that this Green sticker test for manufacturers instead is done as a drive-by test at a different distance.

Likewise I understood that the HRC competition baffle is designed to meet the AMA racing limit of 99 dB and that this likewise was to be measured from 20” (or am I wrong?) at a certain percentage of max RPM.

When I did my somewhat amateurish test at 20” and 45 degrees I was surprised to find that the stock baffle registered ~73-75 dB AT IDLE! And it took only a tiny increase in RPM (barely cracking the throttle) to get to 82 and above. Even numbers in the 90’s were achieved by briefly gassing the engine; I don’t think I got beyond the midrange.

Later I plugged in the competition baffle and was aghast at the large increase in noise. I immediately expected gendarmes to descend upon my home for ever tampering with an engine in such a sinful fashion. Well maybe not, but you know how people are.

More precisely it reminded me of those open piped Harleys that I loathe so much. Not the exhaust note, just the volume. The character of the sound I adored. Very throaty and macho. More basso profundo. I was surprised that my wife didn’t hear it in the basement of our house; I was in the driveway. Mind you every door and window was closed for the A/C.

The numbers I found for this baffle were even more disheartening. Idling gave me numbers of ~101-103 and gassing it brought it over the 110 mark. Dejected I set out to modify the competition baffle as has been described previously on the Yahoo XR650R group (author “rat4go” :) .

Reflections:

1) That competition baffle is much too loud as is for dual-sport use. Sure would sound nice if it weren’t so loud.

2) I can’t seem to recreate the numbers of the testing method above. I wonder what I’m doing differently.

Mind you the Green sticker test and the AMA competition test likely have entirely different testing methods. It just seems that I’m not in the same ballpark.

Kurt Penner

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Kurt,

I just completed the XR650R group mod to the competition baffle. First I cleaned the baffle in gasoline to remove all the soot. Roughed up the inside of the tube with metal grade sandpaper.

Cut the plumbing pipe (1-1/2" diameter) to a length that did not extend into the screen area, only long enough to fit into the solid steel section of the baffle. Cut the downward curving end to a nice contour , finished with a drill and grinding stone. Roughed up the tube. Used a single wrap of stainless steel wire to keep the pipe centered in the 1-9/16" baffle tube. Used JP Weld to bond the two together.

Looks nice. Forces the exhaust toward the ground instead of creating the omnidirection noise pattern of a straight pipe. Very noticable reduction in noise.

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