2   STROKE   VS.    4   STROKE   Engines 

Concluding the calculated results through this exploration, I have verifyed that the 2014 YZ250 2-stroke engine shows higher performance values when compared to the 2014 YZ250F 4-stroke engine. The 2-stroke engine not only has more torque because of its mechanical leverage through its longer stroke length, but also has a larger clearance volume. The larger clearance volume allows for a bigger explosion, which allows the engine to gain even more torque.

 

With more horsepower, torque and a larger clearance volume the 2-stroke would theoretically outrun the 4-stroke with ease. So what Yamaha did to bring the 4-stroke engine up to speed and close off the giant power gap is to increase its compression ratio to an astonishing 13.5 : 1 ratio. To give you an idea how high this ratio really is we can compare it to the BMW S1000RR (2009 superbike championship winner), which had a compression ratio of 14 : 1.