2 Stroke Tech.

[2T_vs_4T]

I'm looking for a web site or forum that has the latest 2 Stroke Tech. Fuel injection or direct injection.
This may be old hat, but, with the direction injection of fuel into a 2 stroke engine once the exhaust port has closed, is an expansion chamber of such an elaborate design, say as used on the new Ossa 300i enduro, really necessary. As the theory behind the sound waves and back pressure has become unnecessary as no fuel is lost out of the exhaust port, with direct injection after it has closed. When you look at the Yamahe 2 stroke outboard engines there is no such elaborate expansion chamber.
Any Tech people out there with their thoughts.
2T_vs_4T.

[David Lahey]

tuned exhausts are for creating pressure waves to help the engine breathe so yes they are a benefit for a 2 stroke with direct or indirect fuel injection
If there is no tuned exhaust on a modern Yamaha 2 stroke outboard motor, I would say it is for the same reason that they were not fitted to run-of-the-mill carburetted 2 stroke outboards (expansion chambers wont fit in the space available)

[2T_vs_4T]

Ok, so the expansion chamber helps remove the exhaust gases. Then why is there no expansion chamber on a Yamaha 2 Stroke outboard with HPDI?

[mustanggrahame]

An expansion chamber on a carburetted 2 stroke puts back fuel and air into the cylinder. On a fuel injected 2 stroke you would still use an expansion chamber to put air back into the cylinder. More air allows more fuel to be added top get more power. Injected or carby same theory with pipe design.
Grahame

[Lozza]

I'm looking for a web site or forum that has the latest 2 Stroke Tech. Fuel injection or direct injection.
This may be old hat, but, with the direction injection of fuel into a 2 stroke engine once the exhaust port has closed, is an expansion chamber of such an elaborate design, say as used on the new Ossa 300i enduro, really necessary. As the theory behind the sound waves and back pressure has become unnecessary as no fuel is lost out of the exhaust port, with direct injection after it has closed. When you look at the Yamahe 2 stroke outboard engines there is no such elaborate expansion chamber.
Any Tech people out there with their thoughts.
2T_vs_4T.

Outboards are different animals the only thing they have in common is they are 2 T engines. The EFI does the fuel the pipe makes the HP it is the over riding influence on an engine.

[2T_vs_4T]

Have any of you seen a 2 stroke diesel motor with a blower. Without a a cut out in the air intake these motors would rev to destruction. I experienced this a a young guy, they rev.

[2T_vs_4T]

So what about a small blower on a 2 Stroke motor for forced induction and direct injection.

[gordon67]

try a search for a commer ts 3 diesel from the 1960s .....cheers

[Mike52]

try a search for a commer ts 3 diesel from the 1960s .....cheers

Try driving one 
Mate , match the sound of a screaming 2/stroke with a supercharger and you've hoon heaven.

tuned exhausts are for creating pressure waves to help the engine breathe so yes they are a benefit for a 2 stroke with direct or indirect fuel injection
If there is no tuned exhaust on a modern Yamaha 2 stroke outboard motor, I would say it is for the same reason that they were not fitted to run-of-the-mill carburetted 2 stroke outboards (expansion chambers wont fit in the space available)

The scavenging/supercharging effect would still work.

[gordon67]

Hi Mike,
I did in the 60s, performance not bad but no engine braking= bad to stop

[Mike52]

Hi Mike,
I did in the 60s, performance not bad but no engine braking= bad to stop

Do you still remember the sound.
Brilliant.
I used to double d clutch and split the diff just to hear it.

[gordon67]

Its something you never forget,....... i still wake up and hear it now after all those years,

[John Orchard]

An expansion chamber create's both positive and negative pulses back at the exhaust port.  You want a negative  (vacuum) pulse at the exhaust port just as it is opening; the quick evacuation of the exhaust gases and the resulting negative pressure in the combustion chamber also aids the fuel coming up the transfer ports, rather than just having crankcase compression doing the job.

Although, with direct injection, there will be no fuel going out the exhaust port, with a positive pulse arriving back at the port just as the piston is closing, a mild form of 'supercharging' effect is a result by pushing some air back into the chamber; hopefully without any of the previously spent exhaust gases.

[pancho]

I'm looking for a web site or forum that has the latest 2 Stroke Tech. Fuel injection or direct injection.
This may be old hat, but, with the direction injection of fuel into a 2 stroke engine once the exhaust port has closed, is an expansion chamber of such an elaborate design, say as used on the new Ossa 300i enduro, really necessary. As the theory behind the sound waves and back pressure has become unnecessary as no fuel is lost out of the exhaust port, with direct injection after it has closed. When you look at the Yamahe 2 stroke outboard engines there is no such elaborate expansion chamber.
Any Tech people out there with their thoughts.
2T_vs_4T.

if you check the inside of the outboard motor leg, guess what you find? an expansion chamber cast into the inner shape of the leg.
pancho

[Lozza]

An expansion chamber create's both positive and negative pulses back at the exhaust port.  You want a negative  (vacuum) pulse at the exhaust port just as it is opening; the quick evacuation of the exhaust gases and the resulting negative pressure in the combustion chamber also aids the fuel coming up the transfer ports, rather than just having crankcase compression doing the job.

Although, with direct injection, there will be no fuel going out the exhaust port, with a positive pulse arriving back at the port just as the piston is closing, a mild form of 'supercharging' effect is a result by pushing some air back into the chamber; hopefully without any of the previously spent exhaust gases.

Erm not really. When the exhaust port opens to the pipe you have a hot high pressure wave, following the high pressure outbound wave is a trough lower than atmospheric pressure. That trough/depression stays there until BDC when that is the lowest pressure in the engine and when most bulk flow happens.After this is when the reflection from the baffle cone arrives to push most of the intake charge back into the cylinder. There never is any 'pushing' through the transfers by the decending piston, there is never any negative pressure in the combustion chamber. You still want the pipe for these reasons.

Correct panch and outboards also use water to vary the diameter of the stinger outlet.