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1. By their nature, ICE engines are only about 20-30% efficient. Meaning 70% of the gasoline that is burnt by them is lost as heat. Formula 1 ICE engines are about 50% efficient, but these engines literally cost tens of millions of dollars and need a specialized team of engineers just to start the motor.

2. Cars have gotten heavier, the engines are producing more power, and despite this they still get better fuel economy than they used to. So they have gotten more efficient when you consider all the variables.

The overwhelming issue as to why we can’t have a 100 MPG 3500 pound car is simply that by design ICE engines aren’t that efficient and we’ve almost reached the practical limit of what we can do with them.

We’d have to switch to a different kind of engine/fuel like nuclear powered cars.

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You don't want that lighter weight body, though, you just think you do. With the lighter weight body you lose a lot of safety features. You have fewer airbags, fewer crumple zones, fewer sensors giving you information about your car and road conditions. Modern vehicles sacrifice that slight bit of efficiency for a much, much safer driving experience.

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Wait until you find out what the "B" in BTU stands for!

The steam engine is an example.

Nope, we're just like any other country

That was a great video to watch.

They made a great point. It cheaper to buy the top shelf vodka than to run it thru the britta filters. Those filters can be expensive. Especially when using it only once 6x.

1979 Honda Civic got 55mpg then.

They actually are.

If you compare a car of today with a car from 20 years ago with the same power and weight the one from today will be a lot more efficient.

We don’t really notice much difference because cars today are much more powerful and faster than before.

However a Mercedes c class is faster today than Lamborghini from the 90’s, and also much more efficient.

I got the v6 accord for power, speed, and reliability. Almost 300hp with a manual is a lot of fun for a daily commuter.

I'd add that there's also limitations placed on absolute efficiency caused by other emissions restrictions; doi: 10.1109/TVT.2015.2405918

A long time ago, this is what ultimately killed gas turbine cars. They were pretty damn efficient for the time but the high combustion temperatures led to greater NOx emissions. The same issue is holding up the development of more efficient high compression ratio piston ICEs.

are there also external combustion enignes?

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A lot of non performance low cc motorcycles get near that mpg. Like the Honda rebel 500 can get 65 I believe, the rebel 300 gets 75. The grom, monkey, and ct/trail can achieve 125mpg.

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Mercedes AMG reached 50% thermal efficiency with their Formula 1 engine about 5 years ago but your point about no “real” engine is still very valid. The F1 engine is using hybrid tech to reach that and is more expensive that many homes, let alone cars. They also are not using standard fuels or oils either. The engine reaches that thermal efficiency not while idling or going at low speeds, it does it at full throttle producing over 1000hp so, while fuel efficient in relation to other F1 engines, I wouldn’t be surprised if the semi truck used to transport the cars from track to track get better MPG.

I‘m not sure I agree you on “nobody asked for more power”. A lot of people don’t want a sluggish car when they are trying to merge. People “ask” via their buying patterns. They’ll look to a V6 if the 4 banger is too puny. They‘ll look to a competitor.

So true! Also cars come with a lot more airbags, safety features and entertainment features than they did 20 years ago.

Also, there just isn't that much more you can do with an ICE engine - it's burning fuel to raise the temperature to generate overpressure which pushed pistons that turn "pedals", which then act through a complicated set of gears and linkages. Whatever you do, it's never going to be super efficient, most of the energy is lost to heating the coolant. And it's a technology that lots of people have already spent a lot of effort on optimizing, meaning most out the easy gains are long gone. Also, it needs to be fairly light and cheap to fit in a car, and work at a wide range of RPMs, torques, power levels, and it has to be reliable and not too complex.

Yep... I just rode in a brand new civic and didn't realize it was a civic until I got out and saw the badge... Assumed it was an accord.

But there's a similar situation going on with hybrids. The 2023 Prius gets slightly better fuel economy as the 2003 Prius. It's gone from a 1.5L engine to a 2.0L engine over that time. The 2023 is 350lbs heavier, explaining a lot of the stagnation in fuel economy.