How to quiet down a Honda CRF150R


Deilke53

The bad news is that the new 150 is very loud, the good news (if any) is that it's so loud stock I doubt the aftermarket companies will be able to make it much louder.

Here's my situation: as a pro-class supermoto racer I'm fully aware that wide open exhausts make a bit more power, and I'm certainly a good enough racer to use every teensy bit of my 450's power at the track, but I'm also very aware and upset over noise issues causing track closures and the constant threat of laws banning ORV use on private property.

I purchased the new crf150r as a playbike replacement for my beloved 150f..and of course after riding the 150r I had the same initial reactions as everyone else "WOW!" better than I could have imagined, and just exactly the bike I've always wanted as a playbike blah blah blah...umm, well, except for the noise:(. I have 20 acres of woods laced with about 2 miles of trails and jumps scaled perfectly for these mid-sized bikes and my son's sx65, but even with 20 acres there is no way that my very cool neighbors wouldn't be bothered by this thing, and there's absolutely no way I'd subject them to it.

SOOO, since nobody is going to offer a truly quiet quiet exhaust, yet another do-it-myself scabrication project begins. The goal is to get very close to totally stock crf150f sound output while keeping as much of the R model's throttle steering/wheelie on demand kick ass power as possible. Enjoy.

Step 1: testing. We used a straightaway to test the stock sound. We made several passes in 4th gear, under load, adjusting our aproach speed so that we'd be in the peak power and truly truly WFO while passing the meter which was placed 50 feet to the side of the track. (a reasonable test, since several of our trails come within 50 feet of a property line) 95dbA!!, yes ninety-F'n-five decibels...at 50 feet!?..good god that IS a very loud minibike. Seems as loud as a 250, only worse since it's almost always pinned.

Step 2: Take it apart.

e.jpg

not much to see here, standard OEM fare, minimal perforation, minimal packing, 1.4" I.D. straight through with a slight curve in the endcap.

Step 3: Try somethin else.

We'll keep it simple and try the basics first. a) Increase exposure to the packing material..I've had great luck using expanded metal to replace stock perf-tubes, it's never ever failed me, and the packing does not burn out as fast as you'd think even on a 450. B) Reduce diameter. Using the new perforated section to taper down, I went from the 1.4" input down to a 1.1" output. c) Divert the flow. it's been my experience that if you let any exhaust flow pass straight through then a great deal of noise will go right along with it..so i've created a diffusing chamber within the last 1.25" of the silencer shell. Now the exhaust flow (which has already seen lots of glass and had its tunnel narrowed a bit) is split by that cone on the center of the back wall and forced to take the long way around to the two (0.7" dia.) exits.

c.jpg a.jpg b.jpg d.jpg

Step 4: Results?

Same test procedure described in step 1.....85dbA. Ten decibels less!..oh, and the bike felt like it hadn't lost any power. Hmmm, off to the dyno..

dyno150r.jpg

All of these runs are corrected hp using the stock knobby..the stock run was done when the bike was new (not broken in yet) out of jetting curiosity, but we did not change the stock jetting. I've seen other stock dyno runs posted (20.7hp broken in with knobby, and BBR got 23hp using a smooth street tire) so my bike seems to be right in line with those other figures. Maybe these exhaust mods lost 1/2hp?..maybe nothing?..either way, -10dbA is much much quieter and also a far greater reduction than you'll ever experience with the typical "optional quiet insert".

Unfortunately, I think WFO85dbA is still too loud for my property so I'll have to try some other solutions, but it's a great start.

-Michael




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