Throttle Position During Acceleration and its effect on FE

[MetroMPG]

Gary: you may be on to something. As someone else pointed out recently, the ScanGauge will tell you when you're in closed/open loop. So that will help find thresholds.

zpiloto: I forgot you had done this already. Just a comment: the BMW folks did not advocate WOT; they suggested 3/4 throttle (to avoid open loop, I presume). I also suspect you're right - that for accelerating up to cruising speed, the method doesn't make a large difference.

Also, if I recall, someone at CleanMPG has done this (acceleration over a fixed distance), but it was for a CVT equipped car (possibly an Escape Hybrid - I forget). I've yet to see if anyone has done it for a manual car. I do believe the transmission type plays a role in which technique is best.

I also think Ben's onto something - the gains may be in using the right acceleration technique when followed immediately by a Codfish.

Brick - are you reading this? Wasn't that one of the first topics you discussed at CMPG? Did you ever do the testing?

[SVOboy]

Did a little testing, oh noes: http://crxmpg.com/accelmpg.html

[krousdb]

I'm thinking that what you referred to as "Jack Rabbit" starts are more like what I would call moderate acceleration. Jack Rabbit usually refers to full throttle. It would be a good data point to the the same but with WOT.

[ZugyNA]

Originally Posted by MetroMPG

Speaking of testing, what would be a valid way to test low load vs high load (low RPM) acceleration?

You could install an adjustable chain on your throttle pivot/cable? You will need a very fine adjustment though...I used heavy copper wire for infinite adjustments.

For the low throttle test maybe at the throttle opening required to maintain 55 mph...or lower? Shift at 1500 RPM?

For the high throttle test...set the chain at about 1/3 throttle or maybe 1/2? Shift at a the same RPM?

You only need to watch the tach.

Need to be careful about where you are testing and that you don't get a stuck throttle.

[JanGeo]

I think if you just did a couple of 0 to 40/50/60 runs with the scangauge resetting it between runs you could tell right away if brisk or slow acceleration would be better - just make sure you do the slow runs first and then repeat for the fast runs going the same distance - just reaching terminal speed sooner for the brisk runs.

[MetroMPG]

Interesting! He goes out with a bang. PS Nice to see the mid 60's coming from your car. (Did you have license plates on during the shenanigans?)

Originally Posted by JanGeo

I think if you just did a couple of 0 to 40/50/60 runs with the scangauge resetting it between runs you could tell right away if brisk or slow acceleration would be better

I think that would be misleading. A simple 0-to-x comparison, resetting as you reached the target speed would only tell you that brisk acceleration uses more fuel.

The big question being addressed is whether the total fuel economy along a given distance is different depending on rate of acceleration in the beginning portion of that distance.

I'm not surprised that the difference is small. It's what zpiloto discovered too, if I remember right.

When I did the 133 mpg round trip using pulse and glide, I used a fairly aggressive amount of throttle (I'm guessing 60% - enough that I could hear "induction noise") up to about 2600 RPM. Which proves nothing without a comparison, except that 133 is attainable with moderate load/low RPM .acceleration.

[SVOboy]

The reason I called it jack rabbit is cuz it was so much faster than normal, I was trying to compare the tortoise and the hare, after all. I should put a note in there about WOT when I get on campus though, la la la.

[JanGeo]

Originally Posted by MetroMPG

I think that would be misleading. A simple 0-to-x comparison, resetting as you reached the target speed would only tell you that brisk acceleration uses more fuel.

That's not what I said, you would go the same distance say .5 miles at a terminal speed of 40/50/60 accelerating slowly and briskly once each run. The point is to see if slow or quick acceleration takes more fuel to get up to speed - it is NOT clear that faster acceleration take more fuel than slow to get up to speed but you do have to keep the test distance constant. Time to go that distance will also vary during the test but that is not being considered. What we may find is that the sooner you get into top gear the better or the slower you burn the fuel the better.

[MetroMPG]

Originally Posted by JanGeo

That's not what I said, you would go the same distance

Whoops - right you are. Hothead that I am, replied too soon & missed that. Sorry!

[JanGeo]

It is a subtle difference - and even going the same distance it will be possible to throw off the results because of the time involved if you get up to speed faster then the average speed would be higher of course that IS the point of the testing. What yeilds the lowest fuel used - what we want to test is how much it takes to get up to speed.