If you have essentially the same road conditions (temp, road surface, rain, headwind, etc.) and drive with virtually the same behavior and drive entirely at highway speed (70-80) only, the identical hybrid version should still get 1+ mpg better (up to 10% better) than the non-hybrid version due to the differences between the "atkinson" cycle setup in the hybrid and the normal (typical) "otto" cycle setup in the non-hybrid version.
The atkinson-cycle runs on a different valve timing/fuel mixture using the same displacement engine but this is optimal only when you have a "booster" like the electric motor in the hybrid. If you put only the atkinson-cycle engine in a car it would run rather wimpy.
Here's something on the subject:
The hybrid will have the higher mpg come in when you exit a high speed lane and pull onto an arterial with much lower speeds (as in pulling off the freeway or interstate to fill-up). So in most real world driving the hybrid setup is going to recoup some of the "losses" from idling at stoplights, slowing down or coasting or needing to run accessories such as air conditioning that can run strictly off the battery.
Have a question for you. I drive daily to work 60 miles away via interstate. the speed limit is 70 mph, but i usually drive at 60 mph in my Tundra. Would a hybrid be of benefit? i am looking at the lincoln mkz hybrid. thanks!
I think testing and tracking these new hybrids on high speed road trips is a great idea. When people first consider purchasing hybrids they want to know what the performance differences are. I'm putting together a discussion group to learn what people want to track about their vehicle, and see if there is an opportunity to build a solution to meet those needs.
If anyone is interested in participating please sign up here: http://bit.ly/fivbYv