Originally Posted by Begle1

There is definitely a law of diminishing returns in effect when it comes to injecting more fuel, which a lot of people don't seem to understand. Added fuel makes more power and more smoke, because no injection system burns all of the fuel it injects.

Let us take a stock engine. It makes no smoke at all. We put injectors into it that are 20% larger than stock, and that increases power a lot and smoke a little. Then we put in injectors that are 50% bigger than stock. Based on the 20% larger injectors, the 50%'ers increase power a lot and smoke a lot. Then we put in injectors that are 80% bigger than stock. Compared to the 50%'ers, the 80%'ers make only a little bit more power but tons of smoke. Any bigger injectors we go than that, are going to make way more smoke but only a little bit more power, or can actually start dropping the power level.

Engines start making smoke before they stop getting power from added fuel. An engine, even one with as efficient an injection system as a common rail, is going to be making more power slightly smoky than it is smokeless. A general rule of thumb is that the voluminous gray-tinged smoke is what you get when you got the fuel quantity just right.

The first little haze you get is definitely not a sign that you have too much fuel, are exceeding the stoichiometric point, and won't benefit from any more added fuel.