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Drilling out the muffler (diffuser?)

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What do I have to do to drill out the diffuser in the muffler? Does it make a difference?

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Look here: http://www.rickramsey.net/CRF250Xmymods.htm#diffuser

I only had a 1/2" drill so I used that and then filed it out until it was flush with the inside of the tube.

I don't know about the performance difference because I haven't ridden it yet. But I have done similar mods to other bikes and it made a big difference. You do need to change the jetting after doing it but the jetting is too lean already and needs changed anyway.

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I have a question about drilling the defuser out. Why drill it out at all? It is easier to just cut the bottom half off of the defuser. That is the part that you normally drill. It still runs very quiet and flows much better. what are the pros and cons of cutting the bottom off as apposed to drilling?

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I thought the same thing. If you look inside the muffler you will see baffles that line up with the rings in the diffuser. It looked to me like the exhaust is being directed in/out/around things to quiet it. The more you cut off the less restriction and thus the louder it will get. I figured if I wanted it loud I would just take the whole diffuser out. Also, you can always cut more off but you can't put it back on. So I thought I would start small.

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I have cut the back off of mine already. I was running with the defuser removed for a long time. I decided i didnt want it obnoxiously loud anymore but i didnt want to give up performance. I got lazy though and cut mine. It is still very quiet. (just a tad louder than stock) I was just wondering why others dont do it that way or recomend it to others. I wonder what a side by side comparison would show.

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A side by side shows really no change at all. My uncle has the same bike and his was the same speed with mine completley removed and his in stock form.

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A side by side shows really no change at all. My uncle has the same bike and his was the same speed with mine completley removed and his in stock form.

I have to ask: Did you rejet and open your airbox too? If not I can completely agree with your statement, but if you rejet and open up your airbox I would think you must weigh more than him. When I did my bike, I could completely tell a difference in it. It seems weird to me that an uncorked bike would perform the same as stock, and weirder that it only "feels" like it fo rme.

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I have to ask: Did you rejet and open your airbox too? If not I can completely agree with your statement, but if you rejet and open up your airbox I would think you must weigh more than him. When I did my bike, I could completely tell a difference in it. It seems weird to me that an uncorked bike would perform the same as stock, and weirder that it only "feels" like it fo rme.

I think you are joking but

they were both jetted properly. My air box was not opened up at the time. We even switched bikes and raced on each other's bikes just to see and they were still the same speed.

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Where is this defuser? In the end of my pipe? Is it the baffle? I have to drill it out. Sorry guys I'm confused.

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You guys are saying pull the defuser out and actually cut some off the end? I'd like to make the bike louder but not obnoxious loud.

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Look under the end of the pipe, at 7 o clock there is a torx screw. Remove it and pull the baffle and you'll see what everyone is talking about. You can drill the blocked end or cut it. I cut because it would be easier to restore to stock if I wanted. I don't think it did anything for me performance wise, didn't effect the jetting still have that small exit diameter. Still didn't like the sound to much like stock, so made a new one with a bigger core diameter.

If you run without the baffle, like many do, there's a little chirp hiss rattle noise in the pipe that some have commented on. Traced it down to the hole where you removed the torx, plug that hole and the sound goes away.

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You guys are saying pull the defuser out and actually cut some off the end? I'd like to make the bike louder but not obnoxious loud.

Very little noise difference it's just a bit louder than stock but under the 96db.

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Yes it does make a differnce. I feel a differnce with the defuser cut or drilled as apposed to stock. I dont notice a huge differnce between defuser cut and defuser removed though....Defuser removed is just louder...When I was wondering about a side by side comparison I was more thinking of noise level and tone. I had already assumed that the cut defuser would make more power than the stock one.

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We even switched bikes and raced on each other's bikes just to see and they were still the same speed.

This is an expected result. There is generally no measureable performance gain with a cut or removed diffuser. It is louder, which makes it "feel" more powerful - same reason all the kids immediately "pipe" their dirtbikes. I read an article a few years ago that showed the 250X to run the best with the stock corked pipe, and actually made less power on the dyno with something like 5 of 6 open (and LOUD) aftermarket pipes. Some do like the louder exhaust note, and that is about the only valid reason to drill the diffuser. If you do drill a hole in your diffuser, no jetting modifications will be necessary.

If there is a power increase from an open exhaust, it will be at the extreme high end of the RPM range, and will typically be accompanied with a loss in low-end power. If you are a trail rider, modifying or removing the exhaust diffuser is the last thing you want to do.

JayC

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Does the bike run better with-out the baffle?

Yes just take it out its not that loud

Its quieter than the r :confused:

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