8cyl = 2000 ish at highway speeds
6cyl = 2500 ish at highway speeds
4cyl = 3000 ish at highway speeds
This is for gasoline passenger vehicles, and will vary a little according to HP/Weight ratio. I've rode in a Corvette that would turn 1500k at 75 mph, and I've rode in a compact turning 3700 @ 75 mph.
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