Silencer bleed off?????

[bclapham]

Hey Guys:

has anyone seen that quite a few of the newer aftermarket 250 shorty silencers have some type of washer welded into the end- i assume it is supposed to help overrev and will bring piston temps up a bit?

is it a worth while mod? it doesnt look hard to do and i am sure BillyHog wont mind firing up the lathe and welder, any ideas on a formula to use or do i cheat and go and measure one up at the shop????? :) :clue:

what about 125s???? i bet they will ping, LOL!!!

thanks

 

[billyghog]

I havn't seen this washer thing you're talking about. E-mail me a picture or post a llink or something. If it really works, then I'd love to make a few. :thumb:

 

[bedell99]

I was wondering the same thing Bruce. I figured it gave the exhaust system more back pressure, which would enhance the "supercharging" effect of the pipe at higher rpm's. Any other thoughts on this.

Erik

 

[Rich Rohrich]

As you change the bleed characteristics you also change the amount of heat trapped in the chamber. Piston crowns have the nasty habit of turning into molten puddles when you get too aggressive playing with this. It's best to tread lightly in this area. :thumb:

 

[bclapham]

Rich:

ive seen this setup on quite a few aftermarket silencers- it seems like it is a trick, just like the SST setup that has the necked down section at the end of the expansion chamber. ive compared a couple of pipes- on the SST and the fatty, the front and mid sections are the same, but the SST is longer and then it has the thinner section- doenst theory say that the shorter pipe should rev better, but i and others have found that the longer SST pipe is more of a topend pipe than the fatty.

as Bedell suggests, it seems like they are trying to do a similar thing with the silencers- run a shorty and get the improved bottom, but have the reducer in the end to trick the engine into thinking it has a longer unit at higher RPMs.

as for piston temps, that wont be a bad thing since my YZ250 runs real rich- i assume because Eric has ported it and the scavenging is improved, once again, ive run out of needle to lean it out.....i was going to ask you how the scavengin works, but ive managed to convince young Billy to buy the Graham Bell books- i just need to convince him to lend them to me now :)

 

[billyghog]

but ive managed to convince young Billy to buy the Graham Bell books- i just need to convince him to lend them to me now :)

Those books are evil - They keep distracting me from doing all the other things I am supposed to do (school, work, etc.) :)

I'll have to read up on the exhaust chapter.

 

[2strok4fun]

seems to me to be just a shortcut way of altering stinger diameter. Maybe a solenoid controlled butterfly valve could give a little overrev, or hole up a bunch of pistons.