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320 Exhaust Mods


virginiatrials
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Has anyone tried removing the perforated tube inside the midbox to make it more like an expansion chamber? With the perforated tube in place it seems that the midbox is really just a muffler. A straight section of pipe would have virtually the same effect performance wise it would seem ,although the exhaust note would be a bit louder(but the bike 2.4lbs.lighter). I am considering combining a gutted midbox and a MX type rear silencer or custom aluminum replica SWM rear box to improve power( and save about 5lbs). I am familiar with making changes to the exhaust systems on piston port engines , but less informed on rotory valve engines, so I am not really sure if this would be a waste of time and effort, or a worthwhile modification. Anyone tried this sort of combination(or any other exhaust mods on the 320)?Any insights /ideas are appreciated. Thanks , Merry Christmas all, Jim

Edited by Virginiatrials
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I wouldn't advise taking out the core from the mid box at all.

In fact it is the opposite that you should be doing by cutting it open , give it a good clean

re-pack and then weld back up.

DO NOT run the midbox empty!!- your engine will eventually pay the price if you do!

(this goes for ANY 2 stroke trials bike - make sure the whole exhaust system is well packed!!)

The best mod to do is run an modern core striaght through type ally silencer.

I have been running this setup for nearly a year and you would not believe the difference

it makes. Bike 'breathes' easier and has a bit more power and revs cleaner.

Another mod i have done is to modify the air box to accept a an air filter with bigger

surface area and fit a less restrictive airbox lid to aid improved air flow.

This combined with correct jetting and the modded full exhaust system

makes a HUGE difference to the bike.

The std silencer is a little too restrictive and heavy , but there is no off the shelf

silencer that will fit , only maybe a flat type TY mono silencer.

I had to get mine custom made-

post-1810-1261119254.jpg

Edited by pedronicman
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Pedronicman,Thanks for the reply. Your setup is exactly what I had in mind with the exception of replacing the midbox with a custom made aluminum through core type silencer with the same internal diameter. The original midbox seems to be nothing more than a heavy, through core type. I removed the airbox lid(as shown on Burgats' bike in the article)last season and it seemed to improve breathing substantially but, I think I will also inlarge the filter surface area as you have. Again,thanks for the help. Cheers, Jim

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As Peter has mentioned, don't muck around with the mid-box; i removed the packing from one i had and the performance suffered (a lot). I had a look at the maddog rear pipe and its good; I converted a WES TY250 rear pipe for the Beta and may now do the same for the SWM.

Have to write up all the mods Peter has done for his 1980 TL320, its made it a very rideable bike

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  • 2 weeks later...

As many have suggested, I opened up my exhaust mid box and found plenty of residue which I removed, What I did'nt find was any sign of packing. Is this correct? Should'nt the box have fiberglass packing? The box showed no sign of having been cut open before. Any suggestions? Thanks and happy new year,Jim

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As many have suggested, I opened up my exhaust mid box and found plenty of residue which I removed, What I did'nt find was any sign of packing. Is this correct? Should'nt the box have fiberglass packing? The box showed no sign of having been cut open before. Any suggestions? Thanks and happy new year,Jim

As i said before-

"I wouldn't advise taking out the core from the mid box at all.

In fact it is the opposite that you should be doing by cutting it open , give it a good clean

re-pack and then weld back up.

DO NOT run the midbox empty!!- your engine will eventually pay the price if you do!

(this goes for ANY 2 stroke trials bike - make sure the whole exhaust system is well packed!!)"

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The core/perforated tube is intact, but no remains of packing were found. What did SWM originally use for packing that would disintigrate entirely? Seems strange that some of the original packing would not be found. Maybe the factory simply accidentally left the packing out of this particular midbox. Thanks, Jim

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The core/perforated tube is intact, but no remains of packing were found. What did SWM originally use for packing that would disintigrate entirely? Seems strange that some of the original packing would not be found. Maybe the factory simply accidentally left the packing out of this particular midbox. Thanks, Jim

It happens, the middle box on my Sherpa had all the packing blown out or burnt away. I suppose it depends upon the type of oil and petroil mixture used over the years as to the state of what's left. Mine on the Sherpa was very clean inside whereas the silencer on a 247 Cota was heavily gummed up and what little packing left was like molasses.

Replacement packing is personal preference I guess, I use Silent Sport wool strands as it is easier to pack in than sheets of fibre matting.

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if it`s in good working order the stock setup works fine.my #1 bike i ride is bone stock and i`ve never needed more power and i`m about 260lbs and ride expert..but if you want to mess around take off the silencer and ride the bike...it`s loud but alot more zap! there`s more power to be found there if you make a different silencer..but don`t ride the bike without one of somekind...

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  • 4 years later...
 

Nope looked at a couple for mine - just out of interest but nothing was close to fitting, to be honest my bike always had that much power when you want it I really don't want any more! I could pull 4th gear up just about any hill you could mention, its possible my disc has been modified as it seems to have a lot more go than the other 280s I had a go on.

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