ok this may be a stupid question but is a 550 motor faster than a 540??

no. The speed is in how many winds the motor has. Lower turns is faster than higher. (ie a 15 turn will be faster than a 27 turn etc)

The #'s you have listed have nothing to do with speed , those #'s are used to designate motor can size. for ex. the stock motor in a 1/10 scale 2wd buggy is a 540 size motor, where the traxxass e-maxx uses 550 can size motors. the diameter of a 540 can motor is the same as a 550 can motor, but the 550 motor is longer, meaning that its armature and magnets are longer which help produce more torque than a shorter 540 can motor.

420 tech is right. The 540 and 550 is the size of t he cans. Longer ones do produce more torque but doesn't really make them any faster.