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

[cwerdna]

(Wasn't sure if I should post here or to cleanmpg.com.)
Ok, so I posted about being new to ScanGauge new to ScanGauge - which gauges should I have up if trying to optimize mileage? and tried reading thru the cleanmpg SHM thread listed at Scangauge: best threads for mileage improvement and FE Ref Aid.pdf.

I've been trying to experiment w/SHM and have a bunch of questions. Part of the prob is that I'm overwhelmed by all the info and discussions (coupled w/my limited free time) and I think SHM isn't suitable for the speeds I'm driving at. I think I'm able to use SHM fine above 45 mph and <60 mph. Holding IGN 13-15 is ok.

Problems/questions:
- At above lower speeds (~46 to 59 ), how hard should I accelerate?
- What can I do about speeds between 65-76 mph, leaning more towards 68-75? If I use IGN 13 to 15, I lose too much speed.
- At 65-75 mph, IGN 18 totally will not allow for acceleration. I can't even maintain speed at IGN 18.
- Is it useless to attempt SHM while maintaing speeds of 68-75? If no, how hard should I accelerate? It seems like I'm well above 2000 rpm (I remember reading staying <2000 rpm in some post) and well above IGN 18 when trying to pulse. Perhaps I'm too lead footed?
- If it's useless, is there another alternative method at those speeds?
- I don't think know I how to properly get into "warp stealth". Not sure if I should care.

Much of my commute is on a highway where the speed limit is 65 mph and driving 65 means you're going somewhat slow and will have to keep closer to the right. That means I run into all sorts of obstacles (cars merging, slowing to exit, and slow cars). That by itself would cause me to brake (wasting energy), not be able to stay in IGN 13-15, having to pulse, etc.

[JimboK]

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.

[alevinemi]

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

[cwerdna]

Since you guys mentioned "hilly terrain", unfortunately most of the highways around here are NOT flat and level. They have gentle slopes and descents all over the place. Hence, I lose even more speed while trying to maintain SHM. :/

[usbseawolf2000]

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).

Safely follow a truck on the highway with Prius: 65 - 85 MPG

Safely follow a truck on the highway with Prius: 65 - 85 MPG

[cwerdna]

Originally Posted by usbseawolf2000

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).

Thanks. Not too many trucks on my route and I'm not real comfortable drafting them, at least not too closely (you look reasonably far). The speeds are too low for my route too. Oh well.

Gotta love those expansion joints. We don't have those over most of our roads here.

[alevinemi]

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

[JimboK]

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.

[usbseawolf2000]

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.

[donee]

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.