best throttle setting for fuel economy

[pickler]

I have the option to alter my throttle setting on my Subaru. there are 3 different settings:

- economy
- sport
- SportSharp

I personally do not see any difference between economy and sport...i think in eco it just keeps the torque converter locked longer before unlocking but i'm not sure. otherwise the throttle maps are both 'numb' meaning the first 5-10% of pedal depression does very little but then it suddenly ramps up to 100% with just 1/3 accelerator pedal depression. For sportsharp, which is my favourite, the throttle is very responsive. The first ~15% pedal input opens the throttle generously. In sportsharp it's very difficult to keep vacuum high and my MPG readout never really goes below 8L/100km during steady throttle functions. But this setting forces me to do mini pulse and glides resulting in high MAP or TPS to keep a steady speed. Shift points are the same if I keep the tranny in D or Drive... it shifts at 2000-2800 RPM based on how fast I roll on the thorttle in normal driving. The SportSharp setting, unlike eco/sport, keeps throttle linear after the first ~15% 'surge' all the way to ~2/3 accelerator input ( So SportSharp is sensitive first ~15% but it starts to tame after,,, good for the track?).

so the question is assuming all other parameters such as shift points, timing and fuel ratio stay the same, which type of throttle setting is best for fuel economy with mix of city and highway?

 

[BrianPetersen]

Those systems in "eco" mode only encourage the driver to drive economically (e.g. by changing the response behaviour of the accelerator pedal), as opposed to actually doing anything.

Anything that causes the transmission to stay in a lower gear (higher revs) than absolutely necessary (e.g. your "sport-sharp" mode) is not going to help economy.

If "eco" actually does keep the torque converter locked more, it should help a little.

These gizmos cannot actually do anything that really improves the efficiency (no "lean cruise", no playing with ignition timing, etc) because they still have to comply with emission standards.

 

[pickler]

that's what I thought! but most people on the subaru forum and eco forums claim otherwise.

 

[BrianPetersen]

What do *they* claim?

It's physically impossible for a push button on the dashboard to change the mechanical gear ratios in the transmission.

Running at anything other than stoichiometric air/fuel is verboten for 3-way-catalyst emission reasons during light-load cruise and gentle driving that predominates normal driving behaviour.

They CAN change transmission calibration (for automatics) but usually only for the worse ("sport" mode) or only for very slim gains at the expense of driveability (by locking up the torque converter and shifting early on the verge of bogging the engine or getting rough shifts in some conditions). Stock, default programming is usually already pretty close to the best that the calibration folks can come up with.

They can and do change the calibration of the accelerator pedal, which is always drive-by-wire nowadays, and by making the driver have to do more in order to "floor it" or get close to full engine load, it encourages more economical driving. But the driver could do exactly the same in the absence of that "eco" button simply by driving more gently.

 

[Tmoose]

Hi Pickler,

with all you monitoring capabilities I'd think you could tell "us" the answer.

One unmeasureable part might be what feels acceptable to you.
IE, if the data says "short shift" at 2300 rpm and open the throttle 37%, and the average speed and trip ET will be the same as brisk conventional driving, but that feels doggy to you, would you drive that way, or even accept the data as real?

 

[gruntguru]

I think a "less sensitive" throttle in the part load area, will be easier to drive economically. Throttle adjustments will be slower and less jerky - invoking less transient enrichment. It also makes it easier to precisely adjust the throttle to requirements and drive smoothly and economically.

je suis charlie

 

[IRstuff]

The ECO setting, by itself, can only do so much. The rest is up to you; if you lead-foot in ECO mode, you'll get crappy mileage.

TTFN
faq731-376

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Of course I can. I can do anything. I can do absolutely anything. I'm an expert!

 

[pickler]

I thought sharper throttle might be better because it avoids high vacuum areas and forces you to do mini pulses and glides thereby effectively eliminating vacuum pumping losses.

 

[Tmoose]

Does your auto trans converter lock up 90% of the time? Does it unlock if the "pulse" is big enough ? or even down shift.

http://ecomodder.com/wiki/index.php/Torque_Converter_Lockup

Some groups note "simply" adding a lock up transmission from a later model is worth a couple of MPG on a 25 mpg Volvo in general mixed driving.

Did you get your fuel and ignition maps to you liking?

 

[pickler]

I advanced ignition timing until knock then backed off 2*. Under low lift cam lobe operation I managed to advance timing as much as 7* without detonation. This really helped with throttle response and you can feel it. Fuel is mostly stoich, I did try lean burn cruise but the car felt horrible and there was tip in or transient knock (upon sudden throttle opening). So I'm running near 15:1 at cruise. My throttle I kept in sport sharp because it shifts faster, the car feels much snapier or livelier and also the TC doesnt unlock much since I think the lock up is based on accelerator pedal not throttle opening (sharper throttle means less accelerator pedal depression). I can pulse without unlock at 40mph or higher speeds. The only time I get a downshift is on highway merging. Otherwise pulse and glides are mostly in locked TC mode in overdrive since I don't need any more torque. My mileage for cruising on highway is horrible at the moment with cold temperatures (-4*f). I barely score 26mpg highway @ speed limit. Summer time I get a much healthier ~33mpg.

 

[pickler]

Under low lift valve mode which is below 3000 RPM the tolerance for ignition timing falls significantly. So I'm running about 5-7* less timing. This reduces torque output but manifold pressure is almost nearly always near atmospheric because the throttle is more open. Not sure if I just switch to high load lift full time with more torque and timing or just use low lift with retarded timing and higher MAP.

 

[Lou Scannon]

My mileage for cruising on highway is horrible at the moment with cold temperatures (-4*f). I barely score 26mpg highway @ speed limit. Summer time I get a much healthier ~33mpg.

How do you account for a 27% increase in cruising fuel consumption with the ambient temperature change?

"Schiefgehen will, was schiefgehen kann" - das Murphygesetz

 

[gruntguru]

Fuel mapping error.
Once the engine has warmed up there should be no difference in economy.

je suis charlie

 

[pickler]

lower temperature air is denser so more power output by engine is needed to keep the same speed. the opposite is true with higher temperatures.

 

[pickler]

http://ecomodder.com/forum/tool-aero-rolling-resistance.php

 

[gruntguru]

Are you referring to aerodynamig drag on the vehicle?

Regardless there is no way the highway economy should be 27% worse. The fuel mapping is incorrect.

je suis charlie

 

[dicer]

That would be full open throttle. All diesels do it, way lower pumping losses.