Throttle Position During Acceleration and its effect on FE

[MetroMPG]

Agreed on your caveat. Regardless of rate of acceleration, you need to avoid turning fuel into brake dust.

[MetroMPG]

Bad news on finding the original BMW reference:

Thank you for your email.

I spoke to several colleagues who are working in the department which was responsible for this kind of study, but obviously the original does not exist anymore. Since the premises on engine development changed drastically since the oil crisis - and this was a long time ago - it was probably not deemed necessary to file every single study.

That's sad, but there's nothing else we can do. Also the study would be of not much help today, because it was based on the technologies of this time, which - especially regarding high-tech engine - have changed a lot.

We regret that we cannot give you another answer.

Yours sincerely,
BMW Mobile Tradition
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[JanGeo]

looking at the graph above it seems 20-30% power at around 2000 rpm is ideal for max efficiency - interesting because that is about 40mph in 5th gear on my xB where I get sometimes 50mpg . . . willl have to check the LOD reading at that speed.

[omgwtfbyobbq]

Word on the street is that during WOT the ECU switches to open loop and a richer mixture to maximize power. Not sure if it's true, but it's what I've always 100% 4real heard. Now the funny thing is, the best FE during acceleration will probably be right before you trigger open loop, so we have to ask, from a stop, how much throttle before open loop in each gear? It's probably different for each car depending on how that manufacturer wants the car to drive, i.e. what's throttle tip-in, what are the gear ratios at the gear we're in, what does the torque curve look like, etc... The only problem is, aside from testing, how can we determine this?

[JanGeo]

ScanGauge tells you if you are open loop or not as well as LOD (% of pwer at current RPM)

[omgwtfbyobbq]

Ooooo... That's pimp. You could build some little clicker that you can feel when approaching open loop via the throttle, according to the SG. Someone test a buncha cars, then patent it and make trillions, or a little less.

[MetroMPG]

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

I would think you'd also want to find best acceleration to cruising speed, and also best acceleration to codfishing.

[SVOboy]

I have no idea about testing, but just a thought: I was beating on my mom's car yesterday and I floored up to 40 in a few seconds and then coasted for ~1 mile to my stop, I wonder.

[Gary Palmer]

Ok, I got a thought on this. If you have a way to monitor the Oxygen Sensor, with a meter, gauge, light's or something, then I would think the most efficient you could get would be if you accelerated as fast as the ecu would allow the firmware to stay in closed loop mode. In closed loop it's monitoring the Oxygen Sensor and the sensor voltage should be oscillating as the controller keep's the fuel adjusted, to swing the sensor voltage up and down. If you accelerate faster than that, you put the system into open loop mode and it's just going to read the air fuel ratio's off of the map's, irrespective of the sensor level's. Whatcha think?

[zpiloto]

Originally Posted by MetroMPG

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

I would think you'd also want to find best acceleration to cruising speed, and also best acceleration to codfishing.

Pick a preset distance say between 1/2-1 mile and accelerate to cruise speed from a stop and at the end point hit the scan gauge and see what the amount is.

Although mine is an automatic I found that to accelerate to cruise speed the amount of fuel difference is very small but the best for me was to accelerate at WOT to 35 MPH and then reduce to 60% load for the rest of the acceleration. Matching what the folks at BMW came up with. Now if traffic would only allow that.