Maximizing Power in Nitro 2 Stroke Engines: A Question on Crankcase Size

[THORPE]

Quick questions but want to let everyone know up front I'm no physics expert I just think a lot. :)

I understand that a small nitro 2 stroke engine (RC cars) pulls the fuel into the crankcase when the piston is on it's up stroke.
I am curious if say I developed a way to make the crankcase larger during the intake stroke and smaller during the down stroke (when it pushes A/F into the combustion chamber), Would there be any added power benefit?

It would seem to have more volume to suck fuel and less volume to compress it to the cylinder equaling more HP.

 

[THORPE]

Quick questions but want to let everyone know up front I'm no physics expert I just think a lot. :)

I understand that a small nitro 2 stroke engine (RC cars) pulls the fuel into the crankcase when the piston is on it's up stroke.
I am curious if say I developed a way to make the crankcase larger during the intake stroke and smaller during the down stroke (when it pushes A/F into the combustion chamber), Would there be any added power benefit?

It would seem to have more volume to suck fuel and less volume to compress it to the cylinder equaling more HP.

After research I've answered my own question.
You can't charge the cylinder anymore than normal because the exhaust port is open longer than the intake on these style engines.

The only way to get more cylinder fill is with tuned exhaust to reflect some of the mixture back into the cylinder before the port is closed.

I'm sure there is a way to redesign it with valves but it would probably fail to support the high rpms these engines produce (30-40,000rpm) and would be heavier and more complicated.

 

[mender]

The internal volume of the crankcase vs the displacement of the piston as it comes down determines the crankcase compression ratio and will affect the power output for several reasons.

 

[THORPE]

The internal volume of the crankcase vs the displacement of the piston as it comes down determines the crankcase compression ratio and will affect the power output for several reasons.

Ok so it may be worth a shot?

I was under the assumption that it would not be feasible much like turbo charging or super charging with sleeve port engines doesn't work.

Seems the only way to get benefits is to come up with a way to get the exhaust port to open first to let exhaust out and also close first so you don't lose the added fuel & air brought into the crankcase then forced into the cylinder.

 

[mender]

It's more for tuning the power curve than for an increase across the board.

Using the tuned pipe is effectively a way to close the exhaust valve earlier in that it inhibits further flow as well as the mild charging effect that was noted.