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Comment by KennyBlanken | Hacker News Reader

38% in the Toyota atkinson cycle engines, which are the top of the industry. Typical is more like 28% for gasoline engines. Then you have automatic transmission efficiency, which is at best ~%80, so now you're down to 30% at best.

More typical: 28% engine thermal efficiency, 75% transmission efficiency means 21% overall efficiency.

So yes, gasoline energy equivalency is pretty meaningless unless you multiply it by 0.2 first.

Gas mileage figures from the EPA and others don't account at all for the time a vehicle spends idling before/after a trip - or even in heavy traffic, just waiting at traffic lights. For example, time parents spend sitting in their cars idling waiting to pick up their kids, time spend idling in coffee and fast food drive-through lines, etc. Start-stop systems help, but a lot of people disable them.

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Among conventional 4-cycle ICE designs there are some recent generator and marine applications near 50%. F1 designed an amazing hybrid system that achieves 50%. Those are the best figures I've seen.

The F1 hybrid design is pretty amazing. The motor–generator is driven by and drives the turbocharger. This allows the turbo to be optimized: When the turbo wants to spin too fast electricity is generated and when the turbo would otherwise not deliver enough pressure (lag) the motor–generator augments the turbo speed. Excess stored power goes to the drive train.

This effectively solves turbo charging, recovering waste heat through all operation phases, eliminating lag and delivering high efficiency. F1 chose not to field it, and I don't know why. I don't know if it will ever be seen in normal applications.

It’s used in the Porsche 992.2 released this year

F1 engines cost seven figures each and are only required to last roughly 20 hours of race time - 7-8 races, each an hour and a half, plus a qualifying session or two per race (barely 15-20 minutes total session time.)

They would probably last a lot longer time if designed for more boring engine speeds, but not cost much less.

Well, the real question is: this amazing tech, assuming they would be able to mass produce it, how efficient would it remain in that case? 40%? 45%?

> Start-stop systems help, but a lot of people disable them.

I've been exposed to a fair amount of different start-stop systems because every rental is different, and some of them are reasonable/good and some of them are awful. My main car is a PHEV, so I'm used to limited idling and that's fine, the big question is what triggers the start and how long does it take to start.

I've been in cars that consistently aren't ready to move when I've pressed the accelerator. Those get disabled everytime I start the car; hopefully I wouldn't buy a broken car like this, but I'd definitely figure out how to disable it if I did. The better ones will start when I reduce brake pressure, so by the time my foot gets to the accelerator, it's ready to move. Those get to stay enabled. In the middle, I might disable them sometimes when they're particularly bothersome, but otherwise leave them be.

> Start-stop systems help, but a lot of people disable them.

I haven’t seen a modern car that let’s you actually disable this versus turn it off for the current ride only, fwiw.

I was able to completely disable it in a new Ford vehicle with an OBD2 cable and since software on my laptop that can modify PCM values

I don’t think people like us register in the grand scheme of things.

I thought CVT transmissions exceeded manual transmissions in efficiency.

Are manual transmission's only 80%?

Who the hell does coffee drive-through?

A huge percentage of America. In most more rural regions, this is the only kind of coffee shop you will find.

Yeah, if you need coffee, then get it before you get behind the wheel.

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