virginiatrials Posted December 18, 2009 Report Share Posted December 18, 2009 (edited) 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 December 18, 2009 by Virginiatrials Quote Link to comment Share on other sites More sharing options...
pedronicman Posted December 18, 2009 Report Share Posted December 18, 2009 (edited) 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- Edited December 18, 2009 by pedronicman Quote Link to comment Share on other sites More sharing options...
virginiatrials Posted December 18, 2009 Author Report Share Posted December 18, 2009 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 Quote Link to comment Share on other sites More sharing options...
malcra Posted December 18, 2009 Report Share Posted December 18, 2009 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 Quote Link to comment Share on other sites More sharing options...
chewy Posted December 18, 2009 Report Share Posted December 18, 2009 It's only a distant memory but when we were riding them as the latest thing we restricted the very last bit of the rear spark arrestor for smoother bottom end. Quote Link to comment Share on other sites More sharing options...
virginiatrials Posted December 31, 2009 Author Report Share Posted December 31, 2009 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 Quote Link to comment Share on other sites More sharing options...
pedronicman Posted December 31, 2009 Report Share Posted December 31, 2009 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!!)" Quote Link to comment Share on other sites More sharing options...
virginiatrials Posted January 1, 2010 Author Report Share Posted January 1, 2010 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 Quote Link to comment Share on other sites More sharing options...
woody Posted January 1, 2010 Report Share Posted January 1, 2010 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. Quote Link to comment Share on other sites More sharing options...
b40rt Posted January 2, 2010 Report Share Posted January 2, 2010 At a push you can use the yellow loft insulation. Probably wont last more than a few months though. Quote Link to comment Share on other sites More sharing options...
jbswm Posted January 2, 2010 Report Share Posted January 2, 2010 jim,when i redid mine i used packing from fmf that i got at the local bike shop.works fine for me..remember if you build a new silencer make 2...johnnyb Quote Link to comment Share on other sites More sharing options...
gups Posted January 6, 2010 Report Share Posted January 6, 2010 Hi is there any advantage in changeing the tail pipe or is it best left alone ? Quote Link to comment Share on other sites More sharing options...
jbswm Posted January 8, 2010 Report Share Posted January 8, 2010 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... Quote Link to comment Share on other sites More sharing options...
iconic558 Posted November 30, 2014 Report Share Posted November 30, 2014 holy thread resurrection Batman.... since this was posted has anyone come across a replacement tailpipe that's a reasonably close fit...I won't add lighter...could anyone make a heavier one Quote Link to comment Share on other sites More sharing options...
twinshock giles Posted November 30, 2014 Report Share Posted November 30, 2014 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. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.