trialtrial Posted April 30, 2015 Report Share Posted April 30, 2015 This story starts off in the enduro world, but takes an interesting turn into the world of trials bikes... I am trying to fix an issue on an 2T enduro bike by improving its lower RPM exhaust scavenging. As I was reading about pipe modelling and design, I came across an interesting article by which an engineer from GM improved the effectiveness of the expansion chamber at lower RPMs by attaching a tuned resonator to the side of the expansion chamber. The article went on to say this was used on a number of production trials bikes and a few enduro bikes. Has anybody seen anything like this hanging off an expansion chamber of a trials bike? I would it expect it to be sometime in the 90s. thanks! Quote Link to comment Share on other sites More sharing options...
lineaway Posted April 30, 2015 Report Share Posted April 30, 2015 http://www.totallyamaha.com/snowmobiles/aaTECH/BoostBottle/boost_bottle_theory.htm Quote Link to comment Share on other sites More sharing options...
axulsuv Posted April 30, 2015 Report Share Posted April 30, 2015 Isn't O'le TT above talking exhaust scavenging and not intake ? From experience I know that anti reversion Headers on a multi cylinder 4 stroke can be used to completely change the torque curve , But I remember some of the 2t exhaust back in the day were kinda weird . But if it worked , wouldn't it still be being played with ? Glenn Quote Link to comment Share on other sites More sharing options...
lineaway Posted April 30, 2015 Report Share Posted April 30, 2015 I was suggesting something easy that would be a positive addition. I was not going to include dialog as my opinion is it would be very hard or lucky to make that work on a 2 stroke. But good luck any way! Quote Link to comment Share on other sites More sharing options...
dadof2 Posted April 30, 2015 Report Share Posted April 30, 2015 (edited) Firstly intake boost bottles. These appeared on Yamaha MX bikes in 1980s. An importer of another leading MX marque when asked when asked why their bikes did not have boost bottle replied "you would be better having a s??t before the race" The volume and shape of a 2T exhaust determines the power characteristics but as the exhaust is a fixed size optimum power is only achieved over a given portion of the rev range. If you had a variable length or variable volume exhaust you can extend the rev range over which power is produced. Hondas variable volume system was called ATAC and was valve operated. Other makers just welded a chamber to the exhaust pipe and relied on the speed of the exhaust gases to act as the valve to the chamber. I am not aware of any of these systems ever being fitted to a production trials bike. I would guess the volume of the resonator to be about 160 to 200cc on a 250 MX bike with connected close to the exhaust port with about a 20mm dia pipe 20 mm long. Low RPM scavenging is usually more to do with transfer port size / shape and expansion chamber outlet diameter / area. Water injection into the exhaust to control exhaust gas temperatures and volume can be used to give similar effects. Edited April 30, 2015 by dadof2 1 Quote Link to comment Share on other sites More sharing options...
lineaway Posted April 30, 2015 Report Share Posted April 30, 2015 Firstly intake boost bottles. These appeared on Yamaha MX bikes in 1980s. An importer of another leading MX marque when asked when asked why their bikes did not have boost bottle replied "you would be better having a s??t before the race" A boost bottle is an intake resonator. Funny about your 80`s comment. This is still a huge market in the world. There are hundreds of different bottles made today! Google boost bottle. Quote Link to comment Share on other sites More sharing options...
p@ul250 Posted April 30, 2015 Report Share Posted April 30, 2015 Is this the sort of thing you're on about? It's fitted to a Yamaha TYZ outfit. Quote Link to comment Share on other sites More sharing options...
mcman56 Posted April 30, 2015 Report Share Posted April 30, 2015 I tried a boost bottle on on a Rev 3 and it did have some effect. I would not say there was more power but it would take very large throttle openings at low rpms and condinue to pull cleaning. Quote Link to comment Share on other sites More sharing options...
trialtrial Posted April 30, 2015 Author Report Share Posted April 30, 2015 p@ul250 - yes I think that is it - I will take a closer look. thanks! 1 Quote Link to comment Share on other sites More sharing options...
steve_earle Posted April 30, 2015 Report Share Posted April 30, 2015 The later TYZ'S had a resonator, Mine was a 98 and it had one, My mates 96 didn't. It gave a better bottom end torque than the standard pipe. 1 Quote Link to comment Share on other sites More sharing options...
trialtrial Posted April 30, 2015 Author Report Share Posted April 30, 2015 The later TYZ'S had a resonator, Mine was a 98 and it had one, My mates 96 didn't. It gave a better bottom end torque than the standard pipe. Perfect - thanks for the info! Quote Link to comment Share on other sites More sharing options...
dadof2 Posted April 30, 2015 Report Share Posted April 30, 2015 Firstly intake boost bottles. These appeared on Yamaha MX bikes in 1980s. An importer of another leading MX marque when asked when asked why their bikes did not have boost bottle replied "you would be better having a s??t before the race" A boost bottle is an intake resonator. Funny about your 80`s comment. This is still a huge market in the world. There are hundreds of different bottles made today! Google boost bottle. Boost bottles, perhaps better described as intake resonance reducers, did presumably work to some extent as several manufacturers, mainly Yamaha fitted them for extended periods. I have never seen independent test power graphs that showed after market bottles gave an overall power gain. Although a lot are advertised, I don't know what actual sales are. There is a lot of stuff offered for sale that does not actually work such as oil additives and magnetic fuel savers. Quote Link to comment Share on other sites More sharing options...
tony27 Posted April 30, 2015 Report Share Posted April 30, 2015 I tried a boost bottle on on a Rev 3 and it did have some effect. I would not say there was more power but it would take very large throttle openings at low rpms and condinue to pull cleaning. Some of what you found will have come from spacing the reed block back, I haven't tried a boost bottle on my YZ465 which is easily done using the next years part off a YZ490 but have used a spacer on the reed block & there is a small difference to how it carburates 1 Quote Link to comment Share on other sites More sharing options...
lineaway Posted May 2, 2015 Report Share Posted May 2, 2015 Boost bottles, perhaps better described as intake resonance reducers, did presumably work to some extent as several manufacturers, mainly Yamaha fitted them for extended periods. I have never seen independent test power graphs that showed after market bottles gave an overall power gain. Although a lot are advertised, I don't know what actual sales are. There is a lot of stuff offered for sale that does not actually work such as oil additives and magnetic fuel savers. Boost bottles designed for the correct displacement do actually work. Trouble is it is just barely noticeable to most riders. I see you are into magnetics. http://nettrax.myvoffice.com/nikkenusa/ShoppingCart/Shop.cfm?CurrPage=CategoryDetail&NextPage=CategoryDetail&CategoryID=646&pid=40016927752570662 Quote Link to comment Share on other sites More sharing options...
pschrauber Posted May 2, 2015 Report Share Posted May 2, 2015 The boost bottle or intake resonator was an invention to reduce back air flow from engine just using ports. With reeds or rotary valves there is no real benefit for this system. That's why they once appeared and now have disappeared. If you need the math for building your own resonator to your engine that is not using reeds or a rotary valve you can sent me a PN. 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.