The engine is in a way set to charge at a max efficiency point, or more precisely, a number of them. Originally it was designed to run constant RPM, but they thought people would find it disturbing when you slowed down and the engine was still revved up. They instead tuned it to run at an efficient point based on the power required for driving.
I would love to see some new engine options. A small 1.0-1.5L turbo would be great, or as you mentioned, a turbo diesel. I've thought about the turbine engine as well, but I'm not sure its the best option for a car based on the extreme heat output.
Love My Volt!
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