Two-Hundred Seventy Six mile highway trip with flats and hills: results

Well I don't mean to flood the forum with posts, but this is quite different than my previous thread which showed a short trip with ideal pulse and WS opportunities and resulted in 72.2 scangauge mpg (my guess is that equals ~70 MFD mpg) over 30 miles.

This trip includes the departure and return drive on I95 and the New Jersey Turnpike from zip codes 21231 to 08831. The results reported here include highway mileage only (no slowing down for ramps or highway approaches) plus slowing down for four tolls and being impeded by a bizarrely behaving grey Prius driver. Blue envy? Traffic was not a problem.

Here are the graphs and data showing elevation and speed





This portion of the trip yielded 60.6 MFD mpg. Interestingly, miles 0-68 (significant hills) showed 62.0 MFD mpg meaning that the second half of the drive yielded ~59.4 mpg. The return trip showed yielded 61.8 mpg according to the MFD with an average speed of 60.63.

This discrepancy (60.6 mpg to NJ and 61.8 mpg return) suggests that further improvements are possible. Turning A/C off could also help a bit. I'm also wondering what the cruise control results would be High-speed tolls, instead of stop and go tolls at miles 32 and 56, see blue line dip, would also help.

Anyhow these efficiency numbers were obtained using an adopted protocol from Hobbit's sweet spot refinement article and are summarized below:

Slight uphill accelerate so that your iMPG = MPH (12.0 kW)
Moderate uphill accelerate so that your iMPG = 0.8xMPH (15.0 kW)
Significant uphill iMPG as close to 0.8MPH as possible
Moderate downhill iMPG =1.3 or 1.5xMPH (8.0-9.0 kW)
Significant downhill use Warp stealth also known as yellow arrow condition, by feathering the gas pedal (0. 0 kW)

Tire pressure was 44 psi, but the stock tires are a bit worn from 50 months of usage.

EDIT: The title can be slightly misleading I guess, there were no "flats" just ~400 ft hills in the first half of the trip and ~50 ft hills in the second half of the trip. Let's keep that in mind before we compare this method to SHM which would be inferior in this terrain and only applies to really FLAT roads.

Also note that as measurements IGN numbers reflect a broad range of engine output. Using kW is more refined and useful for all purposes.

 

Excellent question:

At the times I suspected WS would be in play (PART A of the trip) I would accelerate intently to get the most of WS, during which the car is slowly slowing down. The best example of this is around mile 40 when I reached 74.57 mph, which I would obviously did not interrupt with the brake pedal I used 20 kWs occasionally so that I wouldn't lose momentum below 55 mph, however I would not overpower the terrain.

After MD (mile ~55) which interestingly is where the big hills end (the spike at mile 64 is a bridge) I initially (PART 2A: miles 68 to 100) tried to P&G as if I was on the bigger hills and saw the mpg decrease.

After mile 100 (PART 2B ) I aimed to keep the speeds around 62 +/- 3 or 4 mph.

The conclusion is the following: When I suspected prolonged downhills (80+ ft elevation) and expected that I could use WS, pulsing and WS seemed superior. On smaller hills a more refined version of the original SHM approach seemed to work better.


Thanks for the question, it helped me formulate some important observations. Any ideas?

 

I've written more than a takeaway message below, if you want tfast forward to it go to the paragraphs beginning with bold words

Here's the SHM paradigm:

So I have an issue with SHM as a method and IGN as a reading. First of IGN 18 (the pulse in SHM) and 14 (the shorter prolonged pulse) relate to a wide output of kW that also varies from speed. Also as the refresh rate of SG II is poor the gauge appears to sometimes give erroneous readings for example dropping IGN while you are actually accelerating. Using kW at highway speed allows you to keep looking at one precise parameter. Second even in minor hills holding a steady IGN 14 or even 15 (or even a steady kW output for that matter) means a significant loss of momentum because of the terrain. Try IGN 14 on 70 mph road on a hill and you'll end up at 55 mph in no time. SHM was formulated for "parkway" speeds on flats.

And here's what I use:

Even on minor hills such as those shown in the graph above, past the 68 mile midway point, I believe we need to adopt Hobbit's method of pulsing and gliding with ICE gently on or at steeper downhills using WS.

First, let's agree that kW output, if nothing else, is more precise than IGN in measuring engine output.

Now, let's set a ceiling and a floor for you highest (70 mph) and lowest (60 mph) speed.

The critical part of this technique lies on taking advantage of the downhill portions of hilly terrain.

A ) Assumption: The uphill and downhill portions are protracted or steep. Approach: Enter the uphill at 70 mph. Use 15.0 kW, or more, to reach the crest of the hill at your 60 mph. WS downhill gaining some speed.

B ) Assumption: The uphill and downhill portions are intermediate or small so that WS is not possible. Approach: Reach 65 mph as smoothly as possible. Negotiate the uphill at around 12 kW so that you reach the crest of the hill at 60 mph. ICE-ON glide downhill by adjusting the ICE output to 8.0-9.0 kW (which roughly is IGN 14) until you reach your floor speed limit (60 mph) when you start accelerating again.

Notes:

Tracking your average speed with a cell phone application, as the one shown above is important, to help you set goals and also really informative of your real average speed not a hypothetical one you think you have. If I didn't have that app I would swear my average speed would be more like 64 mph (it was ~61)

In terms of going uphill I'm at a slight disagreement with Hobbit's write-up which essentially suggests that there is not much of an efficiency fall-off even at very high kW (20+).

For ICE operation I use the following guide:

Slight uphill accelerate so that your iMPG = MPH (12.0 kW)
Moderate uphill accelerate so that your iMPG = 0.8xMPH (15.0 kW)
Significant uphill iMPG as close to 0.8MPH as possible
Moderate downhill iMPG =1.3 or 1.5xMPH (8.0-9.0 kW)
Significant downhill use Warp stealth also known as yellow arrow condition, by feathering the gas pedal (0. 0 kW). kW were calculated using Hobbit's SG xgauge.

You can see Hobbit's original approach at http://techno-fandom.org/~hobbit/cars/sweet/refl.html

You can program you scangauge to read kW using by reaching the xgauge icon and then typing in

00 / 4000 8000 0000 / 0000 / 000A 001F 0000 / kw

when asked for TXD / RXF / RXD / MTH / NAM

respectively. These are his calculations and work and I'm only reproducing it here for a more complete picture.

 

Hmm, I have no experience in mountainous terrain, Gen III display, Gen III efficiency and I don't know if you are talking about a single mountaintop or many. Does it display instant MPG?

However even if you're not tracking anything with scangauge, my guess is that the iMPG/MPH ratio could be applicable here. I would try and keep a constant iMPG/IMPH ratio uphill, the lowest you can get away with for your target speed.

Another question would have to do with getting rid of the excess charge accumulating while climbing, is there a way to stop for 5 minutes and blast the A/C? Or stop push the emergency brake (foot brake in the Gen II) and feather the gas pedal or will that tax the drivetrain?