Shorter exhaust opinions for 4-strokes


18 replies to this topic
  • 4literranger485

Posted May 24, 2007 - 11:34 AM

#1

So, i've seen a lot of people commenting on how much they like the shorter exhaust look on the potential 2008 yz450 so i thought of something. in the streetbike world people just cut down the pipe (muffler) so its shorter and put the end cap back on. would this have any adverse affects on the bike?? or would it really just look cooler and be lighter. has anyone done this??

  • never59

Posted May 24, 2007 - 11:52 AM

#2

You would have to be crazy to try something like that if you ask me. Even if you had an extra piple laying around. I am guessing your bike would run like crap but i have never done it so don't let my advice stop you.
The new 1 liter sport bikes have it like you mentioned but there has to be more to it than just chopping an exhaust

  • grayracer513

Posted May 24, 2007 - 12:18 PM

#3

The new, shorter muffler is a baffled type, something like a Flowmaster. Cutting down a glasspack type like almost everyone is currently using might look cool but it will be [COLOR="Red"]LOUD[/COLOR], and you'd run into jetting issues.

Baffled mufflers cannot be shortened because of the internal layout..

  • KJ790

Posted May 24, 2007 - 12:47 PM

#4

Get an aftermarket one. FMF makes some that are relatively cheap ($299 retail) that end at the back of the numberplate and are not any louder than stock. These also do not hurt your performance as cutting the stock one down could.

  • Ranger18

Posted May 24, 2007 - 12:59 PM

#5

I don't think Gray made it clear enough how:crazy: [COLOR="Red"]!!!!! LOUD !!!!! [/COLOR]:ride: your bike would be if you chopped the pipe.:) If you want a shorter pipe, go aftermarket, or wait for the 08. MRD pipes are pretty short; not as short as the 08, but close. Take a look at my garage if you want to see.

  • tys331

Posted May 24, 2007 - 01:01 PM

#6

i had a couple friends cut their muffler so it was barely visible out of the side panel. it did not affect their performance at all but it did make the bike a little bit louder.

BTW this was done on an 99 YZ400F and a 02 YZ426F

  • 4literranger485

Posted May 28, 2007 - 07:47 AM

#7

interesting replies, i for one didnt think it would affect performance that much at all. but i never considered how loud it would be. i've seen people do it on all kinds of streetbikes and you dont really notice the noise that much. personally i've done it to an sv650 and it didnt seem louder. i was just gathering opinions anyhow. i dont really intend to hack up my dr. d haha. but i think most can agree....it does look better!

  • jrny426

Posted May 28, 2007 - 08:02 AM

#8

I recently put the FMF Ti 4 14inch on my 426 and it is alot louder than the burnt out 17 in Q sieries it replaced ,but does have a way more compact look to it.

  • Captaincautious7

Posted May 28, 2007 - 08:13 AM

#9

Me and several others did that modification on our 02 crf 450's. We simply chopped off several inches and reattached the cap. It was very easy to do and I personally did not notice any dramatic difference in noise or performance, although two of us agreed it seemed to increase low end response. I have contemplated doing the same to my 07yzf because of the long cannister, but have not as of yet. I would be curious what anyone thinks of our obvservations on our 02's or were we just imagining the lowend response?

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  • 4literranger485

Posted May 28, 2007 - 11:09 AM

#10

it'd be nice to actually see if there is a noticeable sound level difference, thats probably the deciding factor on whether to do it or not. cause i know the bikes are loud enough as is....i dont need anymore noise. anyone have a decibel-o-meter?? haha

  • Ranger18

Posted May 29, 2007 - 06:36 AM

#11

Me and several others did that modification on our 02 crf 450's. We simply chopped off several inches and reattached the cap. It was very easy to do and I personally did not notice any dramatic difference in noise or performance, although two of us agreed it seemed to increase low end response. I have contemplated doing the same to my 07yzf because of the long cannister, but have not as of yet. I would be curious what anyone thinks of our obvservations on our 02's or were we just imagining the lowend response?


Your probably just imagining the low end responce. If anything you should be getting more top end power. By taking away a few inches of restriction, you are loosing back pressure which inturn kills your low end, but allows for the exhaust to flow more, allowing you to gain top end.

  • Captaincautious7

Posted May 29, 2007 - 11:40 AM

#12

Don't doubt it, but is it all simply about the total length or do you need to seperate the two parts and draw the conclusion based on the length of each part. For instance, I see what you mean about total length, but why do the different manufacturers of aftermarket silencers and headers claim so many diverse performance traits about their own systems and the performance gains of each seperate part when sold seperately and together such as the : silencer and header.Many silencers are sold in different lengths and yet seem to change engine characteristics. When you cut one open their doesn't appear to be any type of spectacular engineering inside although it might just not be obvious to someone like myself. I know the core diameter is smaller on my 07 450 and assuming what you said to be true;would not back pressure have been increased on the 07's as opposed to the 06's therefore increasing low end performance which is exactly the opposite and largest complaint about the 07's?Hey, just asking.

  • grayracer513

Posted May 29, 2007 - 12:58 PM

#13

There is far more to the question than either core diameter or back pressure. If an exhaust system is actually constricted enough to produce any significant back pressure at all, it will have a more deleterious effect on top end than on the lower speed range. The response of an engine to having that pressure relieved will depend on how it was done. If the core diameter is increased, or the exhaust shortened, the benefit, if any, will more than likely occur at the low end of the scale. The reason the top end is less likely to enjoy this kind of thing is founded in how four-stroke exhausts are tuned.

To simplify tremendously, a pressure wave is created when the exhaust valve first opens. This wave travels the length of the pipe at sonic speeds (roughly 1000 fps). When it leaves the end of the pipe, it creates a wave of negative pressure (a partial vacuum) which travels back toward the valve. If this wave is timed correctly, it will reach the exhaust valve just before it closes, and while the intake is beginning to open, and lower the combustion chamber pressures, which will in turn help get the intake charge moving into the chamber more rapidly.

Arbitrarily changing the length of your exhaust system is going to have an effect on this timing that may or may not result in something that you want, even if it does actually lower any back pressure at all.

  • Ranger18

Posted May 29, 2007 - 01:26 PM

#14

Don't doubt it, but is it all simply about the total length or do you need to seperate the two parts and draw the conclusion based on the length of each part. For instance, I see what you mean about total length, but why do the different manufacturers of aftermarket silencers and headers claim so many diverse performance traits about their own systems and the performance gains of each seperate part when sold seperately and together such as the : silencer and header.Many silencers are sold in different lengths and yet seem to change engine characteristics. When you cut one open their doesn't appear to be any type of spectacular engineering inside although it might just not be obvious to someone like myself. I know the core diameter is smaller on my 07 450 and assuming what you said to be true;would not back pressure have been increased on the 07's as opposed to the 06's therefore increasing low end performance which is exactly the opposite and largest complaint about the 07's?Hey, just asking.



Yamaha did decrease the core diameter of the exhaust for 07, which did increase the low end slightly. They did this because the test riders/teams/consumer, wanted more low end than the 06 was offering. So even though the 07 still might need more low end, the 07 has more than the 06. (at least this is what they are claiming, because I have never been on an 07)

  • Captaincautious7

Posted May 29, 2007 - 03:03 PM

#15

I was under the assumption from what I have read here primarily,that the 06's actually had a more radical lowend response as opposed to the 07's smoother transitioned power. It seems to me with what Gray is saying that the most definite negative aspect would be the noise increase and the power characteristics could swing either way. I would be curious to see just how much more of an increase in noise there actually would be in comparison to the change in power characterists considering that you would start with a significantly quieter exhaust as the 07 has to begin with.It would be interesting to try if you had an alternative aftermarket silencer to fit on to your machine after the experiment. You would think that Yamaha has quiet a bit of testing on the length of the silencer but then again they might have just reduced the core and never experimented with the length. I haven't measured an 06 cannister but they appear to be about the same in length with the smaller core. What if Yamaha never tried a shorter length? Interesting topic.

  • grayracer513

Posted May 29, 2007 - 04:45 PM

#16

To the best of my knowledge, the core of the silencer is the same size on both the '06 and '07. The '07 has a smaller end cap outlet diameter, and the rest of the exhaust leading from the head to the muffler is a different configuration as well.

Before making any assumptions as to the root of the power differences, also consider that the '07 has different cams.

  • 4literranger485

Posted May 30, 2007 - 06:34 AM

#17

i didnt expect to get this much information from my thread, thanks gray and all others.

  • Captaincautious7

Posted May 30, 2007 - 01:15 PM

#18

We just need a guinea pig to shorten his silencer and let us know what observations they hear and feel.

  • NAFLASH

Posted May 30, 2007 - 01:39 PM

#19

trust me, it will be a lot louder, takes a little bottom end power away but then again i didn't really notice because it was on a 426... the choice is yours.





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