MPG vs MPH at different throttle settings

[GasSavers_maximilian]

I just finished entering all the data from movies I took of my SG2 while accelerating at a constant throttle in fifth gear on my local "level" and "straight" test road. I found out afterward that mutable glare (from clouds moving I suspect) and my camera's inability to focus consistently on my SG2 (holding a piece of junk mail in front of it for the first instant when it determines the focus was much better) left some data unreadable (and a lot more hard to read), but I have enough to draw conclusions. I would lose either an entire run or nothing, so each piece I collected is complete. Need to put a sun shade over it next time. I ran data for each throttle in both the slightly uphill and slightly downhill directions and they don't differ much, so that redundancy helps fill the gaps. As I increased my throttle settings, the amount of road required for the test run diminished and it became harder to use the exact same piece to account for it not being flat (I seriously doubt it's a consistent grade the whole length). Also, at lower throttles bumps in the road made it very hard to keep my foot steady, especially in the downhill direction (worse bumps in that lane) so the curve jumps around. At higher throttles the greater force of the return spring made it easier to keep things steady and since I needed less road I could restrict my runs to the smoother parts. I also typed in the time data from the movies so I can compute the total energy needed to accelerate to various speeds, which is really what I care about for pulse and glide calculations. I'll need to smooth the curves a bit as well. I'll work that out once my eyes stop hurting. I tried to zero the avg mpg setting for each run, but getting it timed properly and then switched over quickly so I didn't miss anything wasn't practical (at least by myself).



Click for bigger version. The number is the throttle setting and U = uphill and D = downhill.

[GasSavers_maximilian]

Had some insomnia (initiated by my cat jumping on me because I left the bedroom door open) so I worked out the gallons it takes to reach various speeds at each throttle level. Even with all the measurement errors, I think the qualitative trend is pretty clear: more throttle is better up to a point and then diminishing returns is reached. This means that anything above a TPS of around 23 is about the same, so I can make my pulse cycles a little longer than if I used a setting near WOT. This is useful since it minimizes the number of times I have to work the clutch and shift. Ironically, 25 was what I'd been using for my initial P&G trials. Talk about dumb luck, although I may go to 30 to be on the safe side. Since the graphs diverge at higher speeds, maybe I could start at a lower throttle and increase it as I go faster. That should be a good way to blend pulse length and efficiency. Having such a wide range of nearly equivalent throttle positions to choose from should allow me great flexibility when planning P&G around the hills in my routes. I also recorded my mpg when coasting down from 65 on a level, so next I can put it all together to find the optimal min and max P&G speeds and throttle for a level drive. Do that some other time, maybe when my cat jumps on me next.

This is a great example of how being too literal with your instantaneous mpg readout can lead you astray. Mea culpa!

[theholycow]

TPS of around 23 is about the same, so I can make my pulse cycles a little longer than if I used a setting near WOT. This is useful since it minimizes the number of times I have to work the clutch and shift.

I'm not sure I understand that. Do you mean you have to do less work because your pulse takes longer?

In the graph, gallons is gallons per hour, per mile, or per your test distance?

[GasSavers_maximilian]

"Work" was a poor choice; I just meant less personal effort (ie I'm lazy and don't want to shift more than I have to). I realized this morning I'll need to write a computer program to explore all the possible combinations. Spread sheet isn't going to cut it.

Originally Posted by theholycow

In the graph, gallons is gallons per hour, per mile, or per your test distance?

It's absolute gallons consumed from 25 mph to get to that speed at that throttle (in fifth gear). My idea was that since the glide is the payoff I'd want to get up to speed using the least overall fuel. I think that makes sense, anyway; the overall P&G combination calculations will look at total mpg so I guess I'll verify if I was right.

[theholycow]

OIC, it's gallons required to get to target speed - in whatever time/distance it takes to reach that speed.

At a given speed, your glide is going to be the same distance (barring the grade changing). The distance of your pulse would vary by acceleration, I would think; we don't usually measure acceleration per distance but rather per time, however, for fuel economy purposes acceleration per distance is important too.

So, if you use .015 gal to get to a given speed, and then glide 1/2 mile using another .008 gal idling (which will be the same no matter what you did for acceleration), how far did you go on that .023 gal?

[GasSavers_maximilian]

I computed distances and average mpg for the test runs as well. Need to smooth everything out more so my program can interpolate to find intermediary points better. The glide distances are to help me figure out the best top speed for the cycle. Should be interesting to see the end results.

[FrugalFloyd]

Interesting data. They pretty much confirm what I've discovered with my Scion. Accelerating at 65, 70, 75, 80, and 85% LOD come out all about the same. But accelerating at 90 or 95% LOD (for pulsing) hurts my mileage in comparison.

[theholycow]

90% is probably where your system goes to open loop enrichment.

[GasSavers_maximilian]

Originally Posted by SentraSE-R

But accelerating at 90 or 95% LOD (for pulsing) hurts my mileage in comparison.

I didn't capture LOD, but for reference my throttle varies between 5 (not pressed at all) and 85 (jamming down so hard it feels like I'm going to push through the floor).

[GasSavers_maximilian]

Here are the results of the coast down test. I captured both directions since the road isn't quite level. The track wasn't long enough for me to get as low as I'd like, so may go back and start again at a lower speed. Since I only want to see down to 25, I'm not sure it's worth the trip as I can make a guess that'd probably be accurate enough for my purposes. Next I'll determine how much fuel idling consumes, then I can do some P&G calculations.