BSFC maps and fuel economy

[SlowHands]

Interesting indeed. Look at this info: http://www.rangerpowersports.com/tech/?p=25

Following retiredphysicist's numbers, for TorqueNada 35% of max rpm = 1960 rpm, and 75% max torque rpm = 1800 rpm. Looks like my SWAG shift points of 1800-2000 rpm have some basis besides the seat of my pants.

I have found definitely found that Pulse & NICE-ON coasting from 55-50 is much better for FE than steady state 53: I can get 40 P&N vs 32-34 steady.

[retiredphysicist]

Even with standard (non-hybrid) cars, P & G (pulse and glide) is a very viable option when driving at a steady speed below about 40 mph. In my Subaru, the maximum engine efficiency (roughly 31%) is at about 37 HP. However, driving at a steady speed of 35 mph requires only roughly 8 HP (1500 RPM in 5th gear), where the engine thermal efficiency is roughly 24%. In this case, accelerating (pulsing) to 40 mph using 37 HP, and gliding down to 30 mph, would use the engine at maximum efficiency. This is conceptually similar to hybrids, except that the excess pulsed energy is stored as kinetic energy in the moving vehicle, not as electric energy in a battery (and is more efficient). In this example, the pulsed stored kinetic energy for a 1500 Kg vehicle is about 104,900 joules, or 29 watt-hours.
retired physicist

[Right Lane Cruiser]

I get slightly higher numbers for steady state in my vehicle than Ken's truck, but significantly better numbers with P&G -- not surprising given the aerodynamics involved.

I just finished a trip over the weekend covering 366mi with significant hills (most of them I could only do about 27mpg up with really careful throttle control) -- this is on I94 between Milwaukee and Minneapolis -- and I pulled 51.2mpg over that distance.

For comparison, I last drove that route about 4.5 years ago and with flatter segments after this one to finish up the tank (adding an uptick) I ended up with 36mpg. That number included coasting in neutral down the inclines when I could but otherwise fairly typical highway driving. Ignoring the flatter segments which would have been about half the tank, (guessing here as this was way before the SG) the mileage was probably closer to the 33mpg EPA highway rating over the segment in question.

So at an average of 65mph I managed somewhere in the neighborhood of 55% improvement? I can often do even better than that if the terrain is flatter. I have seen segments in the lower 60's with this car and I've actually parked the car after 20+miles on the highway with 57.5mpg showing on the SG. That's what, a 74% improvement? That one was at an average speed of 62mph.

I'd say that P&G is viable at quite a bit higher speeds than just 40mph. It may not be quite as effective, but I think not using it at those speeds would be a mistake.