What causes a car to smoke at high revs?

at hi rev the piston reciprocates at high speed from tdc(top dead centre) to bdc(bottom dead centre),and there's a cycle in which combustion of charges(fuel and air mixture) takes place,and rate of combustion of fuel can't be increased considerably while high speed functioning,so a little charge is left,which is not fully burnt,it may have un burnt hydrocarbons which looks black,and it is exhausted by the engine,so that's the smoke from your car. and there are other reasons to..like engine's valve mechanism is faulty or problem with the spark plug