Jul 11 2008
One thing that has been floating around the heads of many users at www.ecomodder.com for a long time is which method of acceleration proves most effective for fuel economy. It would seem logical that the slow and steady would prevail, but there is also the argument that a quick sprint to cruising speed is best because it gives more high FE cruising time. Even though the acceleration would use more gas it would be balanced by the better FE from cruising or engine off coasting. I chose tonight, the last night I would have my car before heading off to Dartmouth College, to test this idea.
Before getting into the results the test route and procedure needs to be exhausted in order to understand what was actually going on. After warming up the car on the test route I got down to business. There were two theories at test here and I will now describe how each of them was applied in my testing:
- Slow and Steady – For this I used my regular acceleration patterns. I gave very light throttle, shifted into 2nd at 1500 RPM, 3rd at 1500 RPM, 4th at 1250 RPM, and 5th at 1250 RPM. From this point I accelerated in 5th (beginning at 1000 RPM) up to 40 MPH until I hit on of the designated engine off coast (EOC) points. If I was not at a stop and simply pulse and glide (P&G) coasting I would bump in 5th and get back up to speed in the highest gear possible at a slow pace.
- Jack Rabbit – Because extra throttle doesn’t do much at the low RPMS I usually accelerate at I took first gear to 2500 RPM, second to 2000 RPM, and 3rd to 2000 RPM. At this point I shifted straight into 5th as I was already going the mandated 40 MPH for the test. I gave the car 50-60% throttle during these periods of acceleration.
Here’s an edited version of the course I tested this on. It made for a total of 4.79 KM from start to finish. Each number on the map will correspond to a note discussing driving tactic or course layout:
**NOTE: Traffic was not an issue at this test was conducted at midnight on empty roads** On that note, here is a point by point description of the trip:
- Start point, stop sign. Accelerate to 40 MPH
- EOC to point 3.
- Traffic light but I stopped each time to keep it consistent. Accelerate to 40 MPH.
- EOC to point 5.
- Stop sign, accelerate to 40 MPH.
- P&G to 30 MPH.
- Bump start and acclerate to 40 MPH.
- EOC to point 9.
- After taking curve at 25 MPH bump start and accelerate to 30 MPH.
- EOC to point 11.
- Bump on for ~100 yard then EOC to Stop/Start.
Each of the EOCs was begun at the top of a hill or to a stop (the only flat EOC was to the stop). It was odd that each leg of the trip had a hill right in the middle, but that’s how the cookie crumbles I guess.
Ah, the fun stuff, finally! I won’t say I was surprised terribly, but a little bit. The difference isn’t much, but heck, it’s consistent.
Slow and Steady Results
|Engine On %||53||51||51|
|Engine On FE||34.41 MPG||32.31 MPG||32.47 MPG|
|Fuel Used||.228 L||.236 L||.234 L|
|Segment FE||65.53 MPG||63.30 MPG||64.12 MPG|
Jack Rabbit Results
|Engine On %||50||49||49|
|Engine On FE||33.06 MPG||32.22 MPG||32.49 MPG|
|Fuel Used||.226 L||.226 L||.225 L|
|Segment FE||66.29 MPG||66.41 MPG||66.54 MPG|
There is certainly no big gap between these two sets of results, but I believe they are consistent enough to draw a conclusion. The average of all the slow and steady results was 64.32 MPG while jack rabbit acceleration yielded an average of 66.42 MPG for a difference of 3.3%!
I attribute this difference to the increased amount of EOC available with the jack rabbit acceleration. I believe that if there were more distance on each leg the difference would be even greater, but that test will have to wait for another time!