SHM (Super Highway Mode) or alternative for 65-75 mph range? hints?

I think the collective experience of the highway hypermilers is that SHM is pretty much limited to a top speed of 55-60, for reasons you've cited. I watch injector timing (which requires an X-gauge on ScanGauge) at higher speeds, and in sub-60 MPH conditions in hilly terrain (where SHM also is ineffective). I use injector timing to assure the ICE is at least under load but otherwise running as low as possible when it's on, given my speed requirements at the time. At 60+, it's easy to push it over 2000 RPM to accelerate; I try to cap it at 2400 unless traffic or hills insist otherwise.

For a better understanding of warp stealth, see this. Its best use is in hilly terrain where downhill speed can be maintained or gained via warp stealth's free-wheeling effect.

 

I haven't had much luck at these speeds (over 60MPH) either.

SHM doesn't work at these speeds.

Warp stealth requires you to maintain a high SoC, which is difficult if you are running A/C. To do it, your pulses have to be long and slow so the engine recharges the battery, rather than draining it further. Also, at these speeds, you lose momentum much faster on level ground due to wind resistance. A glide from 75 to 65 is much shorter (in time, not sure about distance) than a glide from 55 to 45, giving you less time to find the right accelerator position. Frequently, by the time I 'have it', I've already lost too much speed. That said, I think Warp Stealth is great for speeds of 42-55 MPH. This technique probably works great for plug-in hybrids that maintain high SoC levels.

At these high speeds, I just basically stick with cruise control. Some say they can beat it by keeping constant RPM and slowing uphill/speeding up down, but I don't have a tachometer or scangauge.

-->Adam

 

I discovered this special mode as well. To achieve it easier or at higher speed, external factor helps (safely follow a big, slow vehicle at a good distance).

[ame=http://video.google.com/videoplay?docid=1484126312924696454]Safely follow a truck on the highway with Prius: 65 - 85 MPG[/ame]

 

Yes, truck drafting was one of my surprises with the Prius.

I always believed that to draft a truck, you had to be dangerously close. Although it is true that the benefit degrades with distance, there is a boost at safe distances. Try it sometime on the freeway - follow a truck at a safe distance. Then, pull into the next lane and watch the MPG drop. Then, pull back behind the truck.

-->Adam

 

Safety issues aside, I generally don't get much value out of drafting. In my area, highways largely consist of rolling hills. Trucks tend to keep their speed fairly steady, whereas I vary speed to keep RPM under control. And whatever benefit I might get out of distance drafting probably is lost from having to keep up with what is usually a faster pace than I would choose.

On the other hand, in Seawolf's video the terrain appears relatively flat and speeds manageable. In the unlikely event I would see that, I would consider it, assuming a safe following distance can be maintained. Please, folks, always keep it safe.

 

I am not promoting drafting. The key is to follow at a safe distance, whether it be a trucker trailer, van, big SUV or even a bunch of cars in front. That extra lower air resistance can put the Prius in a very efficient state. I even notice the difference in MPG if I am in the HOV lane with no car in front versus jumping back into the normal lane with cars in front.

 

Hi usb...,

That segment where you did between 65 and 70 mpg , just before the 75 mpg plus bar, looks very much like my SHM mode operation, but with more speed variation. On an average day, I will draw a line of those 67.5 mpg bars for 15 minutes while on the highway. I am not following trucks, however, as they are off doing 65 mph around here. I am not following much of anything else either, until I catch em all up where traffic is slow. I am also not running AC, as its typically cool during that time of the day. So does that mean my aero mods are as good as a 18 wheel 3 seconds ahead - I would like to think so....

SO, I think your doing SHM intermitantly. If you held 70 or 75 mpg instanteneous (iFE), even when it appears you can go higher, you will hold speed steadier. It appears when you let the iFE go up, you dropped down in speed over a period of 20 or so seconds. If you held 70 mpg iFE it would hold speed on the level parts for minutes and minutes, until traffic interferes.

I drop it down to 50 or 60 mpg up grade and the speed will drop to 51 ish over a distance of a mile or so. Then let it rise to 85 ish mpg, maybe 56 mph down grade, for a mile or so. And when the car reaches level lock it right back on 70 mpg at 53 mph.

 

Hi donee,
I am not aware of your aero mods. I am interested in what you did. I had A/C on so I would like to think I got the free A/C for being behind a large vehicle...

 

I know you're not promoting unsafe drafting, and I appreciate that you're emphasizing safety; that's my goal here too. Whether following at three feet behind or three seconds behind, I still call it drafting if the goal is to reduce wind resistance. Maybe that's the wrong way to define it, and I am open to correction.

The point on which we agree is to be safe, regardless of semantics. Hypermilers have taken multiple hits from AAA and various media outlets because of the misguided actions of a small handful of close-in drafters (hypermilers and non-). Wherever the subject arises I want to dispel the notion that we are unsafe -- and emphasize we're among the safest drivers on the road.

 

+1 :thumb:

 

Hi usb...,

Here is the list:

1) flat hub caps made from standard 15 inch wheel Prius trim rings. Road air noise is noticably reduced with these. CAUTION - these are not a good idea anywhere a down-mountain usage of friction brakes is required. Around Chicagoland however, they improve safety besides aerodynamics because they help avoid wet brakes. The Prius uses its friction brakes so rarely, they can become wet from splashes of water from other passing cars. If called upon in a wet condition, it will take a few momemts for them to dry. Additionally, when the car is parked, rain and puddle splashes are kept
off the brake disks which helps reduce, but does not eliminate rusting of the rotors.

2) Upper 1/3 of A pillar turbulator strip

3) Turbulator strip on top of rear view mirrors at estimated seperation point. The mirrors have an upward wedge shape.

4) Flat plate (1/4 inch corrugated plastic) covers over factory blocked grill area where fog lamps usually go.

5) Moved front licence plate from bumper mount to cover middle 1/3 of grill. CAUTION - you need instrumentation to know if this is acceptable in your driving enviorment - keep the engine temp below 95 C, 203 F. Around here my engine temp does not exceed 93 C with this mod and the cooling fans are off except when AC is used. This is probably NOT a good idea in the desert South West, or anyplace with long slow uphill runs. Its probably not a good idea for slow speed heavy use of AC either.

 

I had Dyno-Scan but was not using it at that time. Remember, that video was shot about half a year before Dan discovered the relationship between IGN 14 and the super efficient mode. Dyno-Scan actually show in .5 steps so I can see IGN 13.5, 14.0, 14.5, etc.. It can show me a real-time graph as well.

 

Jim,

I totally agree. Either we like it or not, we are drafting behind other vehicles on the highway. What's dangerous is tailgating. Most tailgators don't do it to reduce aero drag but to save time (supposedly).

 

I was thinking of doing that too. Is it difficult? How did you do it and what extra hardware did you need?

 

From my experience, it seems as though environment conditions have a lot to do with fuel mileage. Example: My morning commute is 78 miles in the morning with very little traffic from Sacrament to Concord no A/C @ 4am. Most of the highway is flat. I average about 43.7MPG. But on the way home @ 3Pm it is bumper to bumper thru fairfield to vacaville and this time of year my A/C is on all the way home. But by the time I end my 78 mile commute home I average 51.2 MPG. Go figure.

A few MPG I can live with, compaired to my 2009 MB E350 that gets 21 MPG downhill in neutral with the engine shut off. (Not literaly)

 

Hi usb...,

I used J hook hardware from Ace. I orignally got four hooks, but found that only two were needed. I took a piece of small black pnuematic tubing, and slit it lengthwise, and tie-wrapped it to the bottom edge of the plate. This prevents the lower edge of the plate from scratching the the lower facia. The bolts hook into the upper part of the lower grill. I used two nuts and two washers on each bolt. One nut and washer behind the plate, and the other nut and washer on the other side. This prevents the J hook from pivoting, and coming loose, even though there are only two J hooks used.