There's a limit of what you can do with small displacement engines. Small CC's means low torque. With the limited power you need to lighten the vehicle to get higher speeds. Once you can't go any smaller, you change the gear ratio to produce more torque at the wheel. This interns increases the RPM and uses more fuel.
Hybrids work better since the motor can run at the perfect effiency. But then there's the battery problems. If you have a large electric motor to make speed then your batteries go dead faster.
Perhaps the solution is to get rid of the internal combustion engine design we have used since, 1700's?
If you have the skill and $$ + tools, you can build a nice little hybrid. Perhaps it would be cheaper to score a salvage Prius like another member here did.
For the rest of us in the U.S. there's the VX, HF, Metro.
How about this? It's small with a small engine? I wonder how this does on the Hwy.
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