[ksa8907]

Originally Posted by Isaac Zachary

There are many factors, but it seems easy for people just shrug off the ones they don't think are important. Lots of people feel SUV's are plenty aerodynamic, that hybrid's don't help that much and most people don't even think about the transmission. But as they say, every little bit helps.

Brake fuel consumption efficiency is something that can't be ignored. Engines get their best efficiency at a certain RPM and a certain load. Stray from that one point and effiency drops. You can't make an engine that's 40% efficient at any RPM/load combination. Even a change of a couple hundred RPM or 10% load can and will change efficiency, maybe not always by a huge percent, but it will change.

So how do you keep the RPM's and load as close to optimal as possible? There are many factors there too, as you said. What would a person buy a minivan with a 600cc engine for? Around town, to cruise down the highway, to climb steep mountain passes in? What kind of gearing would you put in it? Would you put 15 gears in a manual transmission so driver can keep the engine in an optimal range as much as possible? Or throw a 5 speed in there with gearing designed for as much acceleration as possible, keeping it geared really low?f

Note that many manufacturers have placed less powerful engines (what I meant by "small") in their CUV's than their sedans to try to get better fuel mileage in compensation for the worse aerodynamics. A lot of where hybrid's get their better fuel efficiency isn't from regenerative braking, but by keeping the engine smaller (or less powerful) so it will run closer to optimal efficiency loads, but with an electric motor to assist where the engine runs out of power or is too overpowering to be efficient.

I agree, engine size is nearly irrelevant because so many other factors play into it. The engine and gearing is matched to the vehicle and intended use.