Shortened Silencer

[2-Stroke Tom]

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.

The pipes/silencers the Team Green bikes ran depended on who was sponsoring each individual rider. Since I bought my bike off Brian Brown who was sponsored by FMF, it had an FMF pipe and turbine core. Destry bike was the only Team Green bike that I saw that consistently had the welded on sparky. You can clearly see in the picture I pasted (you'll have to copy and paste the whole link) that Destry's bike has the stock silncer with a Cobra sparky welded on. Also, in picture 14, you can see a Team Green rider (don't know if it was Brian Brown, Abbott, Esposito, etc) stting on his 500, and you can seee the sparky insert inside the pipe.

[Motoroost1]

Here is a video of the bike with the shortened silencer out on the trail . Not loud at all . http://youtu.be/Te0J2P0d_7M

[Foxx4Beaver]

sounds good!....I take it that's an old railroad bed?....it'd be cool if you could go in there with a bobcat and set up some doubles/triples to make those long staights more fun!

[Motoroost1]

Yep , it's part of the "rails to trails" program . It is designed essentially for everyone's use with little to no investment by the government to change it or maintain it . So , it is what it is . It's far from the best trail out there , but , it's close to home and provides an easy location to "test and tune" . I have not been on a bike for 30 years , so this is a good way to get my head and body back into the swing of things safely . Better trails are coming

[cobbs]

that video of a stock rm80 smokin that piped ttr220 is just funny that's just solid proof of 2 stroke power!

[Motoroost1]

Stock and worn out . The Suzuki only had 150psi of compression and the TTR230 is brand new That was like salt in the wound for the TTR boys They were doing some seious trash talking for weeks prior to the race   Not any more .

[Polar-Bus]

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 ) .

Personally I think the custom shorty silencer and more power thing is a bit too bold of a claim for a KX500. I'll bet all's your hearing is elevated noise rather than actual power gains.... my favorite bolt on performance comment "It's far easier to loose 4hp than gain 2"...

[Motoroost1]

Now that I've had an opportunity to ride the bike on decent length trail rides ( 30 miles ) with both silencers , my original feeling stands . The engine is slightly stronger in the mid rpm range with the shorty . It's is slightly louder , but minimally . The difference in sound is very small . Does it make more or less top end power ? Who knows ? The mid range is where I spend the vast majority of my riding time , and here , the shorty feels better to me . The great part is that I have 3 different silencers on the shelf . The shorty , a Power Core and a Turbine Core . So , in minutes , I can change at any time if I decide to . I am not trying to convince myself or justify a performance improvement in the shorty simply because I made it and it HAS to be better . Personally , I couldn't care less which one is on the bike . Performance is all that matters and at this stage of the tuning , under the trail conditions that I have ridden ,  the shorty works better . Not sure why . Perhaps it's just the interelationship of some of the key components ( air filter , Rad valve , Gnarly pipe , jetting , riding style etc ) that favors one silencer over the other .  But , no matter how you slice it , like it or lump it , there is a performance difference between the 3 silencers.
I am certainly not suggesting that everyone go out and chop 4" off their Power Core expecting miracles . Until I get develop a better understanding as to why the shorty seems to work ( on my bike ) , it is nothing more than an oddity .  But , an interesting one ( to me at least ) . Everyone has an opinion and I respect that , but , unless it's based upon personal hands on exhaust system development experience , saying it doesn't work , means next to nothing . How would anyone know , unless they've actually done it ? So , here's an opportunity for those with hands on knowledge , to step up and provide real data to explain why things should and shouldn't work . This way we all can learn so our bikes get better and that's what this is really all about . Right

[turdle]

if you had access to a dyno you could find out the difference between all 3 silencers. i am going to  cut and weld a sparky on mine. and i should have access to a dyno this summer. if i get on the dyno i will post up my results.

[Motoroost1]

Unfortunately , I don't . One of the local motocycle shops do have an in house dyno , but , it is reserved exclusively for the street bike guys and they have been unwilling to put an off road bike on it . ()  So , at this point , it's not much of an option unless something there changes .

[RoostDaddy]

you have tried it and noticed a difference, I have too.  Does it make more power, probably not.  But it does allow the motor to work better in certain areas and conditions.  Also, doesnt work quite as well in others.
To me its like running a woods pipe vs. desert pipe.  Do the both work good?  Yes, but depends on where you want power and what type of riding you are doing. 

[Motoroost1]

Yes , exactly