With Direct Injection Would a 2 Stroke Need An Expansion Chamber?

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With Direct Injection Would a 2 Stroke Need An Expansion Chamber?

by Steve

With the basic understanding of how an expansion chamber works by forcing or rebounding unburned fuel/air mixture back in to the cylinder through the exhaust port, and the fact that Direct Injection would not allow unburned fuel mixture into the exhaust, would there be any benefits to having an expansion chamber? And here is another head scratcher, would direct injection eliminate the 'Power Band'??

Does anyone have any feedback on this? How about the PWCs or Skidoos with direct injection? Are they still using expansion chambers?

It will be a great day when the carburetor on a two stroke motorcycle is replaced by direct injection or maybe something even better.

Two Stroke Lover

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With Direct Injection Would a 2 Stroke Need An Expansion Chamber?

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Mar 27, 2011
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Expansion Chamber
by: Anonymous

You need expansion chamber. Without expansion chamber, there is nothing to return the vacuum pulse back and scavenge unburnt fuel/air back into the combustion chamber (supercharge effect). No expansion chamber means no "powerband"

As for direct injection.. Direct injection only controls fuel, not air. Throttle bodies on a DI engine control the air flow. Principle is still the same... just controlled differently.

Dec 04, 2009
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Thanks Tim
by: Steve A

Thanks Tim.

Your comment definitely sheds some light on the the subject. So there is a benefit from the expansion chamber if DFI is used. So without the expansion chamber the amount of trapped air would be lower and we would lose the "Super Charging" effect. Hmmm sounds like there may still be a power band with DFI...

2 Stroke Lover

Nov 16, 2009
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DFI
by: Tim Hickox

DFI doesn't change what the expansion chamber does. Don't confuse AIR with FUEL. DFI controls FUEL; the expansion chamber changes the amount of AIR that remains trapped in the cylinder when the exhaust port closes.

Nov 15, 2009
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Good Question
by: kenny

Hi Steve. A very good question. Some petrol cars have a single point injection system that injects fuel into an inlet manifold whilst still using a carb-type system to provide air to the mix. An idea perhaps?

I heard that they used to have two-stroke diesel trucks that required a turbo to pressurize the air too make it run! A turbo two-stroke dirt bike whoohooo!

I think that the expansion chamber gives you compression too. I know that when I dinged my one thanks too a pine tree, my bikes motor performance changed for the worst.

Back in the day they used to tune two-stroke engines by starting with a long as muffler and cut sections off until the desired tuning was met. That was until a very smart man thought of the expansion chamber.

No powerband? The day that happens is the day I buy a four-stroker! lol

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With Direct Injection Would a 2 Stroke Need An Expansion Chamber?

Comments for With Direct Injection Would a 2 Stroke Need An Expansion Chamber?

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With Direct Injection Would a 2 Stroke Need An Expansion Chamber?