All 2st The future of two strokes

[Motosportz]

Because of this timing of the fuel charge there is no need for the exhaust system to provide a percussive wave that gives the fuel charge sufficient residence time in the cylinder . This means no expansion chambers.

that alone is BIG in regards to packaging the motor in the frame.

 

[rasputin]

Because of this timing of the fuel charge there is no need for the exhaust system to provide a percussive wave that gives the fuel charge sufficient residence time in the cylinder . This means no expansion chambers.
Dyno figures of comparisons between 2 and 4 stroke engines show the 2 stroke producing considerably more torque ( over double at low rpm ) and ofcourse more Hp

So better economy , more torque and power and low emissions !

what orbital are normally comparing in their newer articles are a 450cc two-stroke and a 450 four-stroke engine. and - big surprise to all the two-stroke heads out there - they have found that the two-stroke gives more power.
http://twostrokemotocross.com/2009/06/two-strokes-strike-back/

an issue that is often missed is that a tuned pipe is not only used to "re-gain lost fuel", it is also intended to re-gain lost air. the tuned pipe acts as a supercharger, more or less doubling the bmep, and therefor power. so of course you can go without the tuned pipe, if you double the engine capacity. way to go.

r

 

[wallybean]

Rasputin,

Thank you for clearing that up. I also think that Orbital is having issues with getting their air/fuel injection system to work well above 6000 rpm. I am sure it is just an engineering problem that will be solved. I think that an expansion chamber is always going to be a part of a high performance DI 2 stroke. One of the advantages of the DI is that you can configure the engine architechure however you like(OSSA) and run the expansion chamber out the back which should be at least moderately more protected.

 

[rasputin]

I also think that Orbital is having issues with getting their air/fuel injection system to work well above 6000 rpm.

high rpm are not an "orbital issue", it's a general "direct injection issue". the technology still has not advanced to a level where high rpm are not an issue. even for four-stroke motorcycle engines they still are a major issue. however, the orbital system is capable to go way beyond 6000 rpm, as the 450cc example is showing.

r

 

[rockdancer]

Thats a good article Rasputin . The 450 cc comparison of torque and horsepower on the on -line article look more realistic and are different to same 450 cc graph in this other magazine. Magazine graph shows 2 stroke much better - higher. Strange...
Personally I hope the expansion chamber stays - I like it - looks cool
Exciting times ahead though as long as they dont get too complicated
4 stroke dominance may be just a stage

I for one miss maybe the sound of the 2 strokes at the races...

 

[wallybean]

Thanks good to know. I read the 6000 figure in some article somewhere in my mind. It is probably just another example of old man CRS.