So recently I was looking up posts of other good motocross (I'm looking into buying a second hand one) and I came across a CRF250 and the guy had put dual FMF on her. He made his own "splitter" on the header to split into dual exhausts. He didn't mention any gains anything, but I was wondering did you guys ever try this on a KLX and if it's actually worth it?

Funny thing is I got a spare FMF PC4 at home from my old YZ250f .. If I could weld aluminum i'd be willing to try it on the KLX if it's even worth it

Anybody got a 5c for this?

 

Would the weight gain be offset by enough of a performance gain?

 

One guy posted here previously about doing it on his bike, joking about how it'd allow 40hp etc.

I have a CRF dual exhaust system here I am going to try as soon I get my new testing area sorted out. It won't fit in the normal position without cutting away the battery frame work, but I see I can twist the Y pipe and muffler assembly to the right almost 90deg and then it'll clear the back tire.

It'll look weird with two mufflers jutting out from the right side-one above the other, but it'll serve the purpose as I only go a km to test it and the twist shouldn't effect the outcome performance-wise.

I won't be able to test a/f ratio with it on because there won't be a bung in the CRF system as mine is in the current mid pipe. Drilling the last hole in ss was such a huge effort-even the machine shop took half an hour to drill a big hole into it. I have more bungs; maybe I could get a hole torched into the ss.

I noticed when I had it in place long enough to start the engine that the bulk of exhaust flow comes out the left hand branch which has the larger ID system-even though it's a longer route as it goes off to the left side. The smaller ID section is a straight shot out the back, yet the exhaust prefers the larger ID path.

I have a small battery pack from MotyDesign I can use if testing the duals shows enough improvement to warrant cutting off the battery frame work. This small battery pack spins the Kaw over faster than the battery that's in it! I think that battery framework could be reattached easily by drilling the tubing on both sides of the sawed off connections and bolting it back in place with some round steel up inside where the tubing meets.


If it doesn't test as a negative to performance I may just put it on for the looks someday.

 

if anything 2 mufflers and pipes will probably be double the cost of a single system
and most are already expensive for single setups

 

An after market dual exhaust system would probably be more expensive that single systems. Used CRF dual systems are cheap on eBay, but relocating the battery could be a minor irritation, and it'd still up for grabs as to whether the duals would yield any gain. Probably not on a 250, but ya just never know what's gonna surprise ya.

I think Honda did it to equal out the weight of the exhaust to both sides initially; rather than a performance gain

The CRF250 head pipe is 1 3/8" OD until it gets around the bend from the engine IIRC, and opens up to 1.5" after that. I have a couple original CRF headers here along with the rest of the dual system, and could have one cut, open up the U bend, and rewelded for cheap to follow the necessary bend to fit on the KLX if I ever run out of other farkles to take up my time.

Or just have a 1 3/8 header made to fit the Kaw for aprx $25. I don't have the original KLX header btw.

- Or just test it with the 1.5" OD header I have on there now, and decide whether any more effort is worth the time and trouble

 

You would not get any performance gains by splitting an exhaust system, that is lunacy. It follows the same 'manly' idea that loud mufflers are faster... sorry to burst all your bubbles.

 

That's a big absolute statement that flies in the face of evidence to the contrary in many applications..

The parts are already here and I'm going to try it

 

Honda has produced the highest HP/Liter engines ever produced. None of them used 'dual exhaust'! Most of them were multicylinder and all used individual exhaust tubes to megaphones, some with reverse cones.
Honda 50 twin produced 16BHP, if there was a performance advantage to 'dual exhausts', they would have used it. I doubt that you will get anywhere close to that number, so I would recommend following others till you can reach their limit.
You will get more HP out of a megaphone exhaust system than 'dual exhausts'.
They were also using flat slide carbs on these models to shorten the intake track & about 50 degree ignition advance due to the high rpm.

 

They are trying to make the race bike quieter. If two mufflers made more power every one would have them. It's a KLX 250, I have done all sorts of stuff to mine and it still won't run with my 520 KTM. KLX 250/330/351 is a great bike ride it forever. Altho it is fun to tinker with.

 

The odds are against it adding HP, but there absolutely will be less back pressure with the dual system. Whether the poor little 250 responds to the back pressure change remains to be seen.

I used to be a regular customer of Burns Stainless including buying megaphones, but I don't have access from here. Some members here think that because I am new to the forum that I'm also new to the world of high performance. I'm a 65yo ex Big 3 test driver who is very familiar with the elements of performance.

I'm just playing around with what I have on hand.