Shortened Silencer

[Motoroost1]

I've got a spare stock silencer for my 2003 K5 , and was putting some thought into cutting 4" off the end , and re tig welding it back together again .  Just curious if anyone has ever done this before and what it did ( if anything ) to the power . When I put a PC R304 shorty on my 2007 KX250 , the engine worked better . Just wondering if the same thing would happen with the K5?
My engine already has an FMF Gnarly woods pipe and a Boyesen Rad valve and is rejetted .

[Motorrad]

http://www.kxriders.com/forums/index.php/topic,9171.0.html

[Motoroost1]

Thanks for the link . I've cut 4" off the length and tig welded it all back together . Installation will be in the morning and a test ride soon afterwards . It will be interesting to see how it works compared to the full length silencers .

[dave916]

Thanks for the link . I've cut 4" off the length and tig welded it all back together . Installation will be in the morning and a test ride soon afterwards . It will be interesting to see how it works compared to the full length silencers .

don't think the kx5 revs high enough for the silencers to have much effect on power, saying that there is alot of differant lenghts for the cr500 claiming to vary the power

[Motoroost1]

Did the fabrication work last night and the install this morning . Sounds great and looks good Better than stock or either of my FMF full size silencers  ( Power Core and Turbine Core ) . The sound is not really louder , just deeper . It's rained for a week now so I'll have to wait a couple of days for the trails to dry up to see how it's effected the engine performance ( if at all ) .

[Motoroost1]

To my surprise , a local trail was dry enough to try the bike out . There is no question about it , the engine is stronger with the shortened silencer . The trail was a hard pack service road , and it was easy to see that lower to upper midrange torque was definitely better and the bike accellerated noticeably quicker . It reved more like my 2007 KX250 . This was a GOOD mod that was well worth the small effort to do . Looks better , sounds better and makes more power . I'm happy

[martyestes]

I'm planning on taking off about 3 inches from my Pro Circuit 304.  I'm not into "loud" but I do want to hear that incredible sound when I'm out there with a sea of loud 4strokes.  Back in the early 90's when I raced a CR500, the silencers were quite a bit shorter and the bike sounded incredible. For off-road use, I have a long/quiet Spark Arrestor.

[suva57]

I shortened my stocker at one point too, I forget how much but I cut enough off the front of the muffler so the rear mount lined up with the front mounting hole, then I welded the front mount behind what was the rear mount so that it lined up with the other mounting hole. I cut from the front so I could keep the nice looking stock rounded end and to minimize welding. It sounded awesome, a little louder than stock but with a much sharper bark. It improved low-end power but definitely hurt the top end.
   I ran it for a while like that but eventually switched to an FMF spark arrester when I got tired of welding the core back together.

[cobbs]

fmf and pro circuit silencers suck they are way overkill (too long and congested)for something that should be a performance part I will never run them again Im using an hpd silencer much better performance, sound and look but that's cool you guys actually decided to make them better buy shortening them

[Motoroost1]

I'm not familar with an HPD silencer . Do they have a website ?

[2-Stroke Tom]

I know that Team Green thought shortening the silencer was a good mod. In the link below you can see a picture of Destry Abbott's KX500. You can see how they cut off about 3 inches off of the stock silencer and welded on a Cobra Sparky. They claimed the Sparky had zero effect on power loss, and the stock silencer with 3 inches removed was the best they tested. I also started to throw a bunch of my other pictures of Team Green KX500s onto my photobucket site. Enjoy!

http://s1246.photobucket.com/albums/gg620/rjhansens/?action=view&current=n9n1.jpg#!oZZ15QQcurrentZZhttp%3A%2F%2Fs1246.photobucket.com%2Falbums%2Fgg620%2Frjhansens%2F%3Faction%3Dview%26current%3DKX500e_mail2.jpg

[Motorrad]

The pipe I have off hamels bike.  1. Has a turbine spark arrestor welded on. Not a cobra sparky.   Never seen a cobra on a team bike.  2.  It's stock length.


Just a FYI of the parts I have in my hands..

I know that Team Green thought shortening the silencer was a good mod. In the link below you can see a picture of Destry Abbott's KX500. You can see how they cut off about 3 inches off of the stock silencer and welded on a Cobra Sparky. They claimed the Sparky had zero effect on power loss, and the stock silencer with 3 inches removed was the best they tested. I also started to throw a bunch of my other pictures of Team Green KX500s onto my photobucket site. Enjoy!

http://s1246.photobucket.com/albums/gg620/rjhansens/?action=view&current=n9n1.jpg#!oZZ15QQcurrentZZhttp%3A%2F%2Fs1246.photobucket.com%2Falbums%2Fgg620%2Frjhansens%2F%3Faction%3Dview%26current%3DKX500e_mail2.jpg

[Motorrad]

Didn't mean that to come off short..  Typing on phone

[cobbs]

hpd does have a website hpd inc. But they have changed their inventory a lot they don't sell the silencers I have anymore but they still sell a couple I would take over a fmf or pro circuit but they have to be modified to fit and if I was going to try some thing new I would go CPI , RDZ or FTZ all of those companies are REAL high performance companies with way higher quality, than the generic fmf and pc sorry if any of you guys are fmf or pro circuit fans I just don't like them the pipes aren't too bad but I can't wait to get rid of my fmf gnarly pipe for a cpi cr pipe or rpm pipe then my bike will be complete

[Motoroost1]

So , what's the theory behind silencers ?  If I compare the standard PC 304 unit on my 2007 KX250 to the PC R-304 race unit , the R-304 is much shorter . So , logically , I would assume that less core size would mean less back pressure and potentially greater flow at high rpm . Right ?

If that's the case , why do most people say that the shorter silencer is stronger in the mid rpm range ? In theory , does this mean that it is actually weaker at higher rpm compared to the longer silencer ?

I hate to sound stunned , but , I am new to 2 strokes and I want to make sense of this as best as I can . If the shorter silencer makes more power , why isn't everyone using it ? In my experiment , the shorter silencer was stronger in the mid range for sure . But , I've only done very limited testing so far under one basic riding condition ( service road ) .