Quote: The vast majority of pumping loss is caused by compression followed by friction. To even consider vacuum resisting the piston going down during intake as a significant loss factor just defies logic and common sense IMHO. I'm not saying its not part of the loss, just not a significant part.
Kevin
Ever down shift into low and see how fast you car slows down? That is vaccume right there and that should give you an idea how much work the engine is doing to overcome that vaccume. Remember that a vaccume gauge plugged in the bottom of the carb is gonna show a lot less vaccume than than the top of the piston sees.
Any piston driven engine is very inefficent because of the great loss due to vaccume, compression, and friction. Only a small part of the energy the combustion process produces ends up at the end of the crank and an even smaller amount at the wheels. You can not do a lot about those 3 things, you can run a vaccume pump to increase vaccume under the piston to minimize the effects of vaccume above the piston but a vaccume pump still takes enery to operate, you can run all kinds of friction reduceing tricks like thin rings, narrow bearings, lightweight synthetic oil... but there is still gonna be a lot of friction loss, and to combat compression, well there ain't a lot you can do because reduceing the compression reduces the efficency of the tightly packed fuel burning and reduces the expansion ratio, a high expansion ratio can achived by increasing the compression ratio and by opening the ex valve later, you can reduce the dynamic compression ratio by closeing the intake valve later and this will reduce the compression loss and keep the octane requirment lower but you lose some energy pumping the mix back up the intake tract, you also lose TQ but some of that is gained back by the higher compression/expansion ratios. There are just too many losses of energy in a piston engine to make it very efficent and vaccume is definately high on the list.
I am not causing global warming, I am just trying to hold off a impending Ice Age!
