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is there any good comparison of Hybrid vs EREV efficiency (when main battery is depleted), even with Atkinson cycle ICE for EREV? my understanding was that the main reason for all this complexity in Hybrids was due direct-to-wheel power transfer efficiency, while in EREV there's efficiency loss when converting ICE output to electric current...

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Looking to the Chinese market is insightful, IMO. There's one platform for a luxury sedan, and it gets ~200mi on EV mode (~100MPGe) and then ~400mi on gas. It works out to about 70mpg purely on gas. I'm not sure how it's so high, but I'm guessing a combination of low drag (Cd), efficient small turbocharged engine (you really only need enough power maintain high speed, not accelerate up to it), and lots of regen braking.

BYD and Geely have similar systems. Their ICE are around 47% thermal efficiency so like ~double what you'd expect in a pure ICE car + regen and other bonuses.

https://carnewschina.com/2025/08/02/im-motors-launches-stell...

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