So does this occur during all strokes or only in the power stroke because of the explosion, and when you think about how the piston is free to move side ways how are not all pistons slapping what is keeping them moving linearly in an ideal engine? (mechanics.stackexchange.com)
The ideal engine would have fully variable valve timing, lift and duration, in which the valves would always open at exactly the right point, lift high enough and stay open just the right amount of time for the engine speed and load in use. (en.m.wikipedia.org)
As you shift to a lower gear, the system «blips» the throttle to the ideal engine rpm for a supremely smooth downshift. (nissanusa.com)