Acceleration mini-experiment

[kps]

(Cross-posted from http://www.fitfreak.net/forums/eco-f...ke-granny.html)

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.

[Peakster]

Excellent! I was wanting to do a similar experiment sometime in my car, but it looks like you beat me to it!

[zpiloto]

I'm having a hard time following your test here. Was your fuel total for the whole five mile loop? If so that a lot of varibles for 5 accelerations in such a short distance and the total burns are close. Why not just do runs of 1 mile accelerating to 80kph and holding with the different acceleration techniques and recording the results.

[Hockey4mnhs]

how much harder did u excellerate tho like 500 rpms or like 1k rpms i didnt get that

[kps]

Originally Posted by Peakster

Excellent! I was wanting to do a similar experiment sometime in my car, but it looks like you beat me to it!

You should still do it if you get a chance. Different car, different route, and more runs would all help.

Originally Posted by zpiloto

I'm having a hard time following your test here. Was your fuel total for the whole five mile loop? If so that a lot of varibles for 5 accelerations in such a short distance and the total burns are close. Why not just do runs of 1 mile accelerating to 80kph and holding with the different acceleration techniques and recording the results.

Well, a 'circular' route gets me back to the starting point without having to do 3-point turns on a public road. I don't have a dyno or a closed track, so I take what I can get. Also, the 6 segments are all slightly different, so they should help average out any aspect of a single segment that might unfairly favour one method.

Originally Posted by Hockey4mnhs

how much harder did u excellerate tho like 500 rpms or like 1k rpms i didnt get that

In the slow method (A) I accelerated as gently as I could manage while still visibly accelerating. I got to the maximum speed not long before the deceleration point. (In fact on the long sides of the rectangle I chose the deceleration points as the next clear landmark after I reached 80km/h.)

In the rapid method (B), in the upper gears (3rd through 5th) I held at wide-open throttle until I reached the target RPM or speed. In the lower gears, I didn't get that far since I had trouble shifting quickly enough to stay near the 2500rpm target shift point (the high maximum rpm figures on the B runs come from throttle overrun while shifting).

[MetroMPG]

I'd be interested in seeing a comparo of the various accel. experiments people have run. There's one at CMPG in a Civic CVT, I think SVOBoy did one last year as well.

Also, what's more valid: measuring fuel consumption over a fixed distance (including both the acceleration & cruise parts), or accelerating up to speed (at the different rates being compared) and then driving a fixed distance before recording the MPG?

I'd also like to try doing this. The more cars/results, the merrier.

[Peakster]

I just changed by acceleration style just a few days ago in the Geo. I used to use medium-light throttle and shift from 1st to 2nd @ 7km/h, 3rd @ 30km/h, 4th @ 40km/h, and finally 5th at 50km/h.

Now I use medium-heavy throttle and shift from 1st to 2nd @ 10km/h, 3rd @ 35km/h, skip 4th and go directly into 5th @ 50km/h. The acceleration is a lot quicker and the MPG loss during the new acceleration isn't too detrimental.

Of course, it only works on dry pavement. Winter driving in snow/ice wouldn't work out too well with that technique.

[SVOboy]

http://crxmpg.com/accelmpg.html

Here's mine, *shrug*

[diamondlarry]

I think there is something to the medium-heavy acceleration being better. If you take a look at my gaslog you'll notice a pretty steep increase a few tanks back. It corresponds to my change in acceleration technique. I used to accelerate in each gear to 1500 rpm's at a throttle setting of ~15 according to the SG. At the point where my FE took a leap up was when I switched to accelerating to 2000-2500 rpm's at a load of ~70-75% according to the SG. The TPS reads significantly higher with this technique. I should also note that I usually kill the engine and coast as far as possible once I reach my top/target speed.

[MetroMPG]

And let's not forget the motherthread on this topic: Throttle Position During Acceleration and its effect on FE