I've heard that the Prius II can do good hypermiling < 40, but that there is something that prevents the ICE from shutting off above 40. If that's the case, how can you maximize FE on highway trips. Any way to perform a glide, or at least a slow burn idle at highway speeds in a Prius?

 

The engine will shut off above 40, but it has to keep spinning to prevent the small motor generator from spinning over 10,000 RPM. That drains about 1000 watts from the available energy (either from the battery or from the car's speed) so there's a smaller benefit above 40. The other factor (for any car) is wind resistance, at high speed that's going to slow the car down much quicker than anything else.

 

My experience is that wind resistance is so high on the highway that speeds drops to quickly to make "gliding" a feasible way of driving, it's just to dangerous. Your speed changes form too-fast to too-slow in a mater of seconds. Pulse and Glide in the city works great for me, but i never do it while going faster. The best way to conserve gas on the high way is to "drive as if you had no breaks", i.e. keep a constant speed and let go the accelarator as soon as you see traffic slowing down and let the car roll/glide toward the slowing traffic.

Best advice : Don't speed :-)

 

If it shuts off, does it burn less gas? How do you perform the shutdown, same way you do below 40 with the tap on the accel?Well there are some pretty desolate highways where I live, so I'm not as concerned about that. But they aren't desolate enough to go < 40 mph.

 

Same way the engine shuts off under 40, just take your foot off the gas pedal, then to do a 'powerless' glide you apply very slight pressure to the pedal so that no regen arrows appear on the screen. It burns no gas when the engine is off.

The point of pulse & glide is to get about 3x the distance with the engine off as you got with the engine on, so with wind resistance at high speeds, it's going to be very hard to roll along very far before you need to go into a pulse phase again. At high speed it's probably better to maintain a constant speed for fuel efficiency, although there are probably some situations that P&G might improve FE, most of the time it's not going to help.

 

I view the utility to P&G as only using the engine in it's efficient output range. At highway speeds, that is not a problem, so do not sweat it. The part regarding keeping the engine spin to zero does not apply at highway speeds.

The Atkinson engine in the Prius II (and I, AFAIK), is efficient at 15 kW.

 

I've just noticed cars like Silky Shorts (car 955) getting over 60mpg on the highway with the AC on. Other's seem to get in the low 50s on the highway so I figured there was some magic to learn here.

 

Highway EPA in the Prius II is 51 MPG. I'd have to look at test cycle again to be exact, but speeds in that test are about 50 - 55 MPH. The EPA knocks off 20% from their results to mimic most drivers, so they actually posted approximately 63 MPG.

Hence the first rule of hypermiling: SLOW DOWN

I recently went on a 500 mile day drive all highway driving in the mid 60's MPH, and posted 65 MPG, but that required finding finding a compatible truck I could follow about 5 -8 lane stripes behind.

No other magic I am aware of

 

The EPA highway tests average 48 MPH and go no faster than 60 or so...

There's no fancy tricks to getting good mileage on the highway, it's all about slowing down to take advantage of the lower wind resistance.

 

I agree. I managed to take my FEH to hypermiler status with 75% highway driving through the rolling hills of central CT. The key for me is staying a few MPH UNDER the speed limit. I also shift to 'L' to kick the computer into regen and kill the ICE as soon as speed drops under 40. That obviously doesn't happen on the highway, but, for me, it works well by giving me very fine control over the system.