I ordered an FMF Q4 for my '18 KLX back in April. It's been on backorder since (obviously) and for months I thought that waiting was the prudent choice. However, as the new year has rolled around and spring is now only a few months away I'm wondering if this slip on is worth the wait. I see that I can purchase a Delkevic right now, but there's not much to be learned about these other than a few anecdotal 'it's great!' and 'not too obnoxious!'. Is the difference in sound/power significant?

I have the EJK ready to go, the lid can be pulled off the airbox, I just need the exhaust. Making decisions based off of online reviews is never satisfying, so I turn to this forum of like-minded helpful folks. Wait for the maybe never coming FMF Q4 or pull the trigger on a purchasable Delkevic?

 

One thing about the Delkevic, when I looked. You need to get the 14" can to have a USFS legal spark arrestor. Also, like most aftermarket exhausts, they're not DOT approved. I have a Delkevic exhaust on my XSR700 with the baffle in. It runs as good as stock for sure, but the part I was concerned with was too much noise and if the ECU needed reflashed. As it turns out the ECU didn't need reflashed and when I checked the sound with my $1 decibel meter ap in my phone, I found at about 24" and at a 45° angle the sound level was 87 dB at idle and around 96 dB at around 5000-6000 rpm. Totally reasonable and the change in the tone of the sound was excellent.

The claims for the 14" (350mm) can for a KLX250 is found on the UK site and is 98-100 dB at around 5000-6000 rpm. I'm not too hot on the shortie mufflers, because it just makes the bike obnoxious to others and that drone about 3 feet from your ears when riding longer road rides can drive you nuts. Not too big on the carbon fiber, may be trick, but vibration and such can cause wear at the rivets and eventually fail, where the stainless can won't have much problem at all.

 

Thanks for the feedback! I was looking at the 14", and maybe you have swayed me away from the carbon fiber (I have the camo bike). Good to hear about the sound levels, and performance. The FMF and Yoshi seem to get the highest praise, but are they worth the hype?

 

FWIW... The problem is carbon fiber is strong, but brittle. Vibration around fasteners can crack and elongate the area around holes and eventually cause failure of the holes. The other problem is carbon fiber usually costs more. So you can save money and have a product with longer life.

I think you will get better performance per dollar with either no air box lid or the big KDX200/220 snorkel. I don't know enough to say if it is needed, but an EFI tuner like the EJK would also probably be better money spent. Then the exhaust. If course if part of the thing with the exhaust I put on my 700cc street bike is nice sound, that changes things a bit. That was my reason for the exhaust. I think it looks better and definitely has better tone without being obnoxiously loud, so it was worth it for me. I wasn't going for performance increase, the bike wheelies quite easily and around 70 hp is fine by me. A small bore dual sport, power might be more important.

I also recommend buying a buck phone ap to do a sound check if you pull the baffle. My ap was "noisee". Just checked sitting here watching a baseball replay at lower volume, it was around 55 dB. In my shopping for my exhaust it wasn't about increased horsepower or even volume, but rather the sound coming out. I wanted a nice rumble, but at a level that wouldn't bother someone standing near me, like people at a crosswalk in town.

 

I'd wait for an FMF Megabomb Header.
All of the aftermarket mufflers are the same in that they are a beercan with a perforated tube running down the middle and some fiberglass wadding stuffed around it.

I'd get a Delcovic. They're cheap, good looking, well made stainless steel mufflers (most FMF's are aluminum). Be sure to get one with a quiet insert. They offer lots of different ones. I ran this one that did not have an insert and it was insanely loud!

 

I still like the disc style muffler set up @tooter has. Tune the sound as well as the power. And from what I read in another forum, more discs doesn't make for more power. There will be a number that provides the best performance for what one wants. The posting I read, the rider found his best number for the bike he was running was 7 discs, six would reduce performance and eight would also reduce the performance. But regardless for most riders tuning for the sound is the nice part, thye can determine just how loud the bike is. My 650 ran 8 I think, been a while, and wasn't too loud according to my wife, the neighbor, beside whose bedroom window I'd start the bike at 6:00 am, and from what I heard when a friend did a drive by. It actually was a bit too loud for me as a rider, having the exhaust a couple feet beneath my ears.

 

I tried every combination of disks, and 3 works best for my 300. It revs freely to redline while idling and running only slightly louder than stock. Too many disks kills off low rpm torque.

Supertrapp disk technology is fascinating.

How They Work

The tunable disc design was developed 30 years ago by an avid dirt bike rider and aeronautical engineer. The gap between the radial discs is smaller on the inside than it is on the outside. This creates an expansion chamber which allows the exhaust gases to move faster from the high pressure inside of the exhaust to the low pressure outside. The low pressure helps pull the exhaust gases out of the motor which in turn allows more fresh air and fuel to enter the motor on the next stroke. This is what is meant by a scavenging effect. More exhaust out. More fresh air and fuel in. More torque and horsepower out

 

You should have seen the first muffler/silencers Dr. Paul Moeller, founder of Supertrapp, made. The first was the Xduser, which looked like a sideways mini-pie tin. Super quiet and blew smoke rings when the throttle was blipped on my TM125. Worked great on two strokes making them totally civilized in volume... and smoke ring blowing cool.



The first Supertrapp was one of those clamp on short silencers that actually looked like a sweet potato, thus the one on my friend's 125 Pursang was dubbed the sweet potato. I can't even find a picture of one.
Then came the first 3" disc black glass packed megaphone with the disc setup. From there it progressed to what is now the Supertrapp setups with the 3" still available and four inch for most motorcycle use, a five inch for automobiles.

 

He seemed to be onto the concept of exhaust exiting radially rather than linearly. However old, it's still a novel idea. Today, most of Supertrapp's marketing is focused on Harleys.



I even adapted a Supertrapp to my Honda Ruckus. It ran great with it.

 

They're also into the car market as well. Both racing and street.