2015 Ford F-150 unveiled

rjstractor wrote:

Wes Tausend wrote:
One of the things I personally do not understand well is how automatic start/stop technology can help much, but it obviously does. My question is with pumping losses which would seem to still exist even if a cylinder did not have fuel to fire. A V-8, for instance, would still be "dragging" 4 extra pistons along whether or not they contributed to power. In my mind I finally resolved this by thinking that when only 4 cylinders fire, the thottle must be open further to maintain speed and this therefore reduces vacuum. Under high vacuum, the unequal lack of topside piston pressure as opposed to bottom crankcase atmospheric pressure is part of normal pumping losses, but an open throttle allows closer-to-atmospheric pressure topside, same as nominal crankcase pressure bottomside. I'm guessing perhaps that is the sole thrift gain.

Wes, when you say "stop/start technology", I think you are actually referring to cylinder deactivation, which is something totally different. Start/stop is when the engine actually shuts down when the vehicle is warmed up and the vehicle is stopped, like at a traffic light. My hybrid does this, as do most hybrids. When my defroster is running, the engine doesn't stop. In city driving, I would estimate start/stop adds about 2-3 mpg.