Older the engine, poorer the mpg.

Guys,
I do not know much about engines so please keep it simple lol.

Can someone explain to me why older engines, like a 1977 Winnebago with a 440 gets 5 mpg while a newer 2013 engine gets like 20 mpg?

What happened between 1970 and 2013 to engines that make the mpg jump so much?

Was there single technological breakthrough that made engines jump from single to double digit mpg?

There wasn't necessarily a single breakthrough to engines between 1970 and 2013, but several moderate changes. I would consider the major contributors to be electronic engine controls (electronic fuel injection becoming standard, multiple sensors to enable a pretty consistent stoichiometric 14.7:1 air:fuel ratio, etc.) and improvements in manufacturing technologies and materials. The improvements in engine manufacturing lead to better tolerances which increased the efficiency of the engine and also enabled the manufacturers to use lighter weight oils. The lighter weight oils reduced parasitic losses and therefore improved fuel economy.

There have been a lot of advancements independent of the engine that contribute to improved fuel economy as well. For example, composites have made significant strides since the 70's as well. Building the RV out of modern composites helps reduce weight without sacrificing strength. Also, with composites and modern manufacturing the vehicle shape can be made much more aerodynamically which is a large factor in fuel economy. And don't forget that the way the fuel economy is calculated today may not result in a true representation of the fuel economy each driver will experience. Driving style and geographical location play a role in actual economy as well.

-Rod

Excellent post

There have been a lot of advancements independent of the engine that contribute to improved fuel economy as well.

4 more significant contributions come to mind, which have boosted fuel efficiency over the years.

Transmissions: There have been vast improvements in transmissions, especially automatic transmissions, most of which have been directed towards fuel efficiency improvements. Overdrive top gears, lock-up torque converters and electronic controls all improved fuel economy.

Tires: Modern tires are designed to operate at higher pressures, and have more efficient designs, all of which lower rolling resistance. This means the tires roll more easily and improve fuel efficiency.

Combustion chamber design: Specifically, combustion chamber shape, use of opposed valves, higher compression pressures and lightweight engine materials all improve thermodynamic efficiency, that is, more of the fuel is turned into kinetic energy, and relatively less is wasted in heat and unburned fuel.

Turbochargers: Turbos are wonderful at reclaiming thermal energy and converting it into motion. They also allow for smaller, lighter, more compact and lower friction engines, all of which boost fuel efficiency.