A. Slow acceleration. Shifts at 2500rpm.
B. Rapid acceleration. WOT in higher gears. Shifts around 2500 – 3000 rpm in lower gears, and at 2500rpm in higher gears. Some wheelspin in 1st and/or 2nd gear due to the gravel road surface.
Note that cruising and deceleration were the same in both cases.

The car is a 2007 Fit LX with standard transmission.


The course is a 7.8km (approx. 5 mile) rural block chosen for minimal conflicting traffic. (Nevertheless, one run had to be aborted due to Mennonites.) I stop at 5 points -- each corner and one additional location -- and add one additional deceleration and re-acceleration.

1. IJKL 1.7km.
   IJ - Accelerate from standstill to 80km/h and hold.
   JK - Decelerate (in gear, no throttle).
   KL - Brake to a stop (clutch / neutral).
2. LMNP 1.4km.
   LM - Accelerate from standstill to 80km/h and hold.
   MN - Decelerate (in gear, no throttle).
   NP - Brake to a stop (clutch / neutral).
3. PQRS 0.9km.
   PQ - Accelerate from standstill to 70km/h and hold. (With gentle acceleration, there is not room to reach 80km/h.)
   QR - Decelerate (in gear, no throttle).
   RS - Brake to a stop (clutch / neutral).
4. STUV 1.6km.
   ST - Accelerate from standstill to 80km/h and hold.
   TU - Decelerate (in gear, no throttle).
   UV - Brake to a stop (clutch / neutral).
5. VWX 1.5km.
   VW - Accelerate from standstill to 80km/h and hold.
   WX - Decelerate (in gear, no throttle). Final speed is around 50km/h.
6. XYZI 0.7km.
   XY - Accelerate from 50km/h to 80km/h and hold.
   YZ - Decelerate (in gear, no throttle).
   ZI - Brake to a stop (clutch / neutral).

I made three runs using each method, alternating methods to try to avoid any changes due to other factors. The runs weren't perfect; in the B cases I sometimes overshot the target speed, and was unable to shift from 1st and 2nd quickly enough to shift at the target 2500rpm. On trials 3A and 3B other traffic slowed me briefly (part of segments LM and ST respectively).

In each case I had the car off briefly while recording information prior to the initial run or from the previous run. I turned the engine on, reset the Scangauge trip counter, and drove.


Run    Initial   Max   Avg   Max   Max    Fuel
      Air Water Water Speed Speed Engine  Eff .
      °C   °C    °C   km/h  km/h   RPM   L/100km
1A    10   82    84    51    82    2844   6.6
1B    14   86    84    61    83    3559   6.3
2A    14   84    84    53    81    2710   6.6
2B    13   85    84    64    86    3308   6.5
3A    13   84    83    51    79    2738   6.5
3B    10   82    83    62    85    3513   6.2


Rapid acceleration to cruising speed is more fuel-efficient than slow acceleration. Presumably the greater fraction of the drive spent in high gear at cruising speed more than makes up for the hard acceleration.

(Cross-posted to gassavers.org)

 

Have you tried slow acceleration, but shifting at 2500-3000 (basically, the same rpm as your fast acceleration one)? This is the RPM I shift at, unless I'm cruising at a very flat low speed limit zone. When climbing mountains I shift at 4k or 4.5k

I tried doing it your way. I actualy got the same mileage, which I thought was odd. I am beginning to think DBW really makes everyone's driving habits the same using software. I know that when you lead foot, DBW might restrict the throttle. The same is if you feather foot it, that it actually has a high throttle than you'd think (people have complained this makes the car appear more powerful than it is). One guy said when he put around 1/4th the pedal, it was actually 3/4th the throttle.

 

Interesting read! It's nice to see people go out and actually do some tests on their own.

I am still concerned that we don't have the control we think we do over fuel economy. I guess I have never had full confidence in any fuel injected vehicle that operates with a computer system. Now, I think you can only keep up on your maintenance and keep your tires inflated properly to achieve the best fuel economy. Everything else is at the mercy of programmed computer logic!

Keep up the good work!. I'd love to "see the light" on this issue.

 

I was trying to shift at 2500rpm in both versions; it's just that under heavy throttle I wasn't able to shift out of first accurately since it accelerated too fast. From second I kept closer to 2500rpm and from third on I could shift accurately.

I intend to do one or more shift-point tests eventually; probably something like 2500rpm vs 3500rpm first, and then, assuming there's a definitive winner, another against a more extreme point, e.g. 2000rpm vs 2500rpm.

It's not 'my way' yet; I'm still working on putting it into practice in daily driving. I wouldn't really expect much difference. I think the test course pretty much maximizes the possible difference from acceleration technique, since the segments were not much longer than the distance required to accelerate slowly, but in one run the difference was only 0.1L/100km.

In city driving, you run into the problem that faster acceleration means that you may reach a higher speed only to encounter traffic or a light, which means throwing away more energy than if you had still been accelerating at a lower speed. I guess the ideal would be to accelerate quickly to some lower speed, but you can't always predict what will happen ahead. In highway driving, acceleration is pretty much irrelevant. The main result, really, is that you don't actually improve your mileage by driving like a Prius owner on weed.

I know that the car does go WOT (and open-loop) when floored; however, since I only have a Scangauge and not a data logger, I wasn't able to monitor the throttle continuously during the test; I had to look at the road occasionally. The next test I want to do, actually, is between full throttle acceleration (Method B of this test) and acceleration that is rapid but not heavy enough to send the ECU into open-loop mode.

I guess my background gives me the opposite perspective: the ECU does something very precise (although unfortunately Honda doesn't tell us what) -- give it the same conditions and it'll always do the same thing. A needle and float seem so unpredictable and uncontrollable by comparison.

 

wow this is an interesting idea. any final results on which method is better?

i have a scangauge too, i might have to try this on some future tanks

 

I think your data at higher speeds, in 5th gear, agrees with the Pulse & Glide technique. That being accelerate quickly(relative to slow and with in reason) to reach the top speed you desire then shut the car off and turn it back on to coast. For if you accelerate slowly to the top you desire it will take a much longer time hence wasting more fuel and you will not be coasting LONGER or the same amount of time that it took you to reach the top speed.

Does that make sense?

 

"one run had to be aborted due to Mennonites."

That made my day. Seriously.

 

I read on a forum somewhere that the logic is that a smaller engine, such as the one in the Fit, are more efficient at wide open throttle (WOT) due to the reduction in pumping losses, versus having the engine work against a high vacuum with the throttle blade virtually closed. Of course, it would also get you to cruising speed much quicker as well. I have to say I've always been skeptical of the technique, but others swear by it. The forum I read about it on was a hybrid car forum, so maybe the electric motor assist had something to do with it. I believe the guy posting about it was driving an Insight.

 

WOT doesn't do anything but waste fuel. do you have a scangauge? if not, get one. it isn't about RPM, but about THROTTLE POSITION

 

I postulate that accelerating quickly and cruising CAN be pretty efficient overall, as long as you can cruise LONG enough for the higher fuel efficiency to offset the low efficiency of rapid acceleration.

So I'd say if you want to haul a$$ and cruise, be careful - make sure you have a good long cruise ahead.

 

Exactly!

I miss wrote/typed (instead of spoke) earlier you typically would like to coast at least 2 times as far that it takes you to consume the amount of fuel used to reach the desired speed.

 

Run    Initial   Max   Avg   Max   Max    Fuel
      Air Water Water Speed Speed Engine  Eff .
      °C   °C    °C   km/h  km/h   RPM   L/100km
1A    10   82    84    51    82    2844   6.6
1B    14   86    84    61    83    3559   6.3
2A    14   84    84    53    81    2710   6.6
2B    13   85    84    64    86    3308   6.5
3A    13   84    83    51    79    2738   6.5
3B    10   82    83    62    85    3513   6.2

what is this????

maybe you can clean it up or post as an image?

 

me too. no more heavy accelerating around the CPS's or MCC's I guess.