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.

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.





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..

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 curiousity, 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

Great post Mike.
How is the pitch, does it still sound like it's got some balls.

It sounds really really good...balls-a-plenty. Crudely splitting the flow like that I expected it might sound a bit raspy or out of tune, but not at all.

Its just quieter.

Excellent post.

ben

Clever! now if you could only extend the canister a few inches. I bet that would help alot.

Very cool, you should be an assistant on Myth Busters with your skills..
Seriously..

Good work on the muffler mods. We just spent the day breaking in my wife's 150. At 12k rpm this bike really is loud. The freakin muffler outlet is the same size as my 450! No wonder it's loud.

Please go into the aftermarket exhaust business.:worthy:

awesome post (and research):worthy:

Great work and outstanding post Michael. :thumbsup:

I agree!! great job, especially when AMA Sports is going to be very strict with their 99db limit in '07.
Let me know when you have the mod available. Again great job. Tdub

Just one tip on using the Dynojet. Make several runs till your results stabilize. They will be much more accurate and repeatable.

Every one needs to click on the Gas Can in the top right of mikes post and add to his reputation!!! That was an awesome post!!!

That looks awesome! Two thumbs up..

This is one of the best posts I have seen on this site. This is exactly the type of thing we all need to keep our sport alive.

I am writing a letter to Honda about how stupidly loud they made this bike:mad:

Please send the test results to Honda usa, it is very important!!! also send copies to Jimmy Lewis at Dirt rider mag, he is very helpful with the sound issue. I bet he will do an article on your design. You deserve some recognition for your excellent work!!:applause: :thumbsup:

First off, good job. Secondly, because I am the type of person to burst your bubble, here goes: This just confirms that when you quiet a bike down, it kills the bottem-end power, with the least effect at peak power. I would much prefer a quiet bike, but I will not sacifice power spread. Especially on a 150.

Thanks for all the compliments. I'm not planning offering anything like this for sale, I was more hoping that others in similar situations would be inspired to break out some tools and either try out their own ideas or copy mine...losing that last vicious 10db is quite a bit, and might be quiet enough for some?

Isn't that strange how the modified (and I assume more flow restrictive) exhaust carried its power further into the revs than stock? That was exactly opposite of what I expected. I know back-to-back dyno runs with my crf450 show that my race exhaust (ProC Ti4) makes a few more ponies, but more importantly keeps making power long after the curve drops off with the stock pipe.

I don't think we can expect the aftermarkets to get into a battle of who can make the quietest pipe while maintaining stock power until there is significant demand...but if I can lose 10db through an afternoon of guesswork and dumb luck, just think what a few really smart folks who do exhausts for a living could accomplish through a week's worth of trial and error. While I understand that do-it-yourselfers have it a easy since we don't need to worry about manufacturability, unit cost, patent violations, consumer perception, and all the other little issues like the manufacturers do.

Anyway, I'm looking forward to trying some other solutions..and the great thing with the 150r is that even if I do have to lose a few hp in order to get really really super quiet the end result willl still be a very fast, fun, and great handling playbike.

Just wait till a riding area near you get shut down. Then a quiet bike would make all the sense in the world. But it would be to late to do any good. :ride:

Treehopper, it's OK, there's no bubble to burst. Like I said in the beggining, I race loud 450s quite successfully..55-60hp, I'm good enough to use every bit of it, so for me 150s are playbikes. A few horsepower makes no difference to me in this case, I promise you I'll still be very fast on it.

News to me that restrictive pipes lose mostly bottom end. I've only ever experienced the opposite. Even so, remember that the dyno runs posted are 4th gear roll-ons with stock jetting, so don't worry you'll never be going 30mph in 4th on this bike anyway.

My nearest neighbors all claimed that they could either just barely hear me riding, or not hear me at all when I was on my 150f..and I'm gonna do my best to make it that way with the 150r, and my next playbike, and my next playbike. Hopefully by then (if ORVs still exist) I'll be able to simply order a an incredibly quiet pipe that doesn't give up much power.

You should patent your design and then lease the design to the aftermarket pipe companies. You could make a few $$ and hopefully the aftermarket pipe companies will make even quieter pipes.

Great Post! Please keep us informed on the progress. My son rides the CRF150R, close to residential property. Sound DB is a very critical thing. We have lost other riding locations before due to DB.:thumbsup: