"hard" acceleration means something less than 50 sec to get from 22 to 44mph (that would be a=.02g), but the equation says that you'd get even better performance to do it in 2 sec (which would get you from 0 to 60 in about 5 seconds). I can't imagine smoothly going to a glide after that kind of neck-jerking, tho. Just letting the engine idle down before you kill it would probably take a few seconds.

I think the varying engine efficiency is accounted for in my hill-climbing experiments which led to the equation involving C, the number which lies between 30 and 50 for a HCH.