Pulse & glide in a non-hybrid?

Highway P&G is a very complicated, vehicle, enviorment and operator dependant thing. Hypermilers usually do not P&G on level highway, but attempt to use the lowest RPM. They say its something to do with the lowest number of engine pumps (to minimise pumping losses) per mile.

That said, P&G below the highway aerodynamics regime (say under 45 mph in most cars) will result in a great improvement in Otto Cycle engined cars. The ratio of engine effiency at best versus low outputs tells this story. A Gen II Prius engine has an effiency of 35 % at optimul load and RPM, and 25 % at a lower load and RPM (12.5 HP). So, 35/25 would indicate a fuel economy improvement of 40 % for a properly implementd P&G operation over steady cruise. 77 mpg, versus 55 mpg is realistic experienced result and a 40 % improvement in fuel economy.

An Otto engined car has an optimum efficiency of about 25 % and a low output efficiency of 10 %. So, a 150 percent improvement should be realisable in a manual transmission Otto engined car. Wayne driving his Electric Power Steering Accord at 48 mpg, versus the combinde 25 mpg rating is illustrative of this, but still not 1.5 times better, but close.