the most that increase the right question would be to VARY why don't you solve each thing gaining weight or increasing.
for me, if you are talking about petrol cars sucked, I think that the answer ? obvious, since the only things that are modifiable (for example, in the iaw 6f 8f 16f, etc.) are the times of injection advance and duration).
I would add that, in the case of engines from the point of view of the suction, and then with the dynamic effects different from the original ? absolutely necessary to vary the timing of injection: this is true both for the loan and for the duration. also in the search of the desired ratio of the lambda ? a fundamental correction of the times.

I think we deduce that, for me, the answer ? you.