Hey folks,
I'm sort of new to this hobby, so excuse the crazy questions.... What is long and short stroke? What exactly is the difference between long stroke and short stroke engines? Are there any differences in performance between the two? Thanks in advance!

Pylanton, The stroke is the movement up and down of the piston, it can be measured in inches or mm. A long stroke engine will make it's power at a lower rpm and will make more torque at this engine speed. A short stroke engine will make it's power up high in the rpm band (less torque, more raw horsepower) because it has less distance to travel from the top to the bottom of the stroke, hence higher rpm. Listen to a Harley(long stroke twin cyl) verses an inline four crotch rocket(short stroke) and you will hear the difference!
Most long stroke engines are for slower scale flying with lots of pull where a short stroke is for more speed and higher performance.
I hope this helped. Fly High.
Suptter

Generally speaking with our model engines there's not enough difference for one to be called a long stroke and another short stroke. The thing that makes the difference though is not the length of the stroke but the fact that the bore is bigger in a "short stroke" engine. The circumference of the bore increases by a factor of pi (circumference = Diam x pi) so this means that even though the height of the ports is slightly less (for the same timing) it's more than made up for by the extra room around the bore for these ports. This means they can have a bigger area for gas to flow through them which gives better breathing at higher revs. It hurts low down torque though because the velocity of transfer mixture is lower.

A 2 stroke model engine designed for low down torque won't necessarily be a "long stroke" but it will be timed differently and the ports will be smaller (including the transfer passages) to keep the mixture velocity high. A good example of this is the latest OS LA's which have done away with the boost port so now the mixture has to move faster through the remaining two ports.

If the bore is bigger than the stroke, an engine is oversquare. Conversely, if the stroke is bigger than the bore, the engine is undersquare. If they are even? Square.

As a general rule, engines that are "short stroke" are going to be considered those that are oversquare. In order to be able to turn at the RPMs that they do, the stroke has to be shortened enough that the piston acceleration will not result in enough force on the conrod, crankpin, or wrist pin to fail. If you imagine the piston having to change directions at both the top and bottom of the bore, and imagine two vastly different engines, one very oversquare, and one very under, the piston velocity and the acceleration felt by the undersquare engine is going to be much greater than the oversquare.

By shortening the stroke, you reduce the internal forces being transferred, and as such, allow the engine to rev out further. Once the basic operational parameters are set in terms of engine geometry, timing and port work can optimize the power output.

One of the biggest advantages of the short stroke engine is that it can often be made smaller than a long stroke.

Although it's got nothing to do with model engines, the most oversquare production engine I know of was the one used in the little 4 cylinder Ford Anglia 105E. It had a bore/stroke of 80.9mm x 48.4mm to give 997cc and pumped out a massive 39HP