Open pipe on a 4 stroke ?

[jimson]

G'day viewers, I'm just after some information on running a 4stroke bike With an open exhaust pipe no muffler. Does this create valve & carbie problems ? Thanks Jimson

[mick25]

TT500 / XT500 seem to come alive with no Mufflers down low that is .
And sound great that's how they got there Nic name THUMPER .

[Oldfart]

They require a tuned length of around 28 inches with a little bit of back pressure.

[80-85 husky]

I think the "you will burn the valves if you take off the muffler " was a furphy to keep mufflers on

[jimg1au]

speedway bikes ran for years with no mufflers yes its is a tuned length will not damage your motor one little bit
you need to tune it properly

[Daryl Jones]

They require a tuned length of around 28 inches with a little bit of back pressure.

Depends on the Revs.   At 11,000rpm  20" is nearer to ideal.



I use a drilled metal cone for a baffle, area of drilled holes is greater than pipe end.
Gives something for the machine examiner to tick the box as an "effective muffler".

cheers, Daryl.

[Oldfart]

An old method was to paint the pipe and were the paint stopped burning was close to tuned length.
 

[Flipper]

An old method was to paint the pipe and were the paint stopped burning was close to tuned length.

I was told by a pretty competent tuner back in the 80's that it was 'look for the heat ring', then 'cut 1 inch beyond that' for the perfect tuned length. Stainless pipes worked well, as the was a very obvious blue/yellow ring where the exhaust gases collected.

[sleepy]

In the 70's when single Hondas where being palyed with, changing the muffler to something more "flowing" generaly required the carb to be richened and some found out if they didn't make thing a little richer the exhaust valve sometimes burnt. With retunning to suit it works fine if you can stand the noise.

Ask Mr Google about organ theory and exhaust pipes. A lot of research was done with books written on the subjects back in the 60's and 70's.

[Tim754]

Pops Yoshimura tuned length for high comp SL125.

Other versions SL125


Oh the prices for the racing crank and close ratio gear sets....

[jimson]

Thanks for your input everyone, I'm trying to get my Honda 350 twin to run right with open pipes. I need to jet the carbbies right & work out if the pipe should be baffled to create some back pressure. Jimson

[80-85 husky]

what about your ears??

[fred99999au]

Pardon??

[80-85 husky]

whaaat??

[fred99999au]

I SAID PARDON?!!!