Basic questions for fuel effiency

[justjohn]

Originally Posted by smvssd

Accelerating slowly and keeping your engine RPM's low are the best way to get the best gas mileage. Keep an eye on your tach and if you have a newer car they often give the instant gas milage. It takes practice but once you get it right you will be able so save a lot of money on gas.

Current ecomodder opinion is that this is generally false. It keeps you in the low efficiency part of the bsfc graph.

However, astoundingly few people have actually tested it.

[Joenavy85]

Originally Posted by justjohn

Current ecomodder opinion is that this is generally false. It keeps you in the low efficiency part of the bsfc graph.

However, astoundingly few people have actually tested it.

I've actually tested it with the help of one of my friends, using my ScanGaugeII, I didn't write down anything to make it official, but there is a slight improvement by "higher load" acceleration compared to slow steady acceleration when going onto a highway. BUT, slow steady acceleration is better in the city when you can't always predict a stop, or there are short distances between stops.

[Kodak]

I try to use the term 'situational acceleration' because of how frequently traffic and conditions impact acceleration rates.

But, when it comes down to the open road, that's another thing.

JoeNavy - were the results substantial enough to overcome external variables? I'd be curious to see the results of a test on this. Reminds me of something the EPA did a while back if I'm not mistaken.

If I buy the SG-e, maybe I'll try a little A-B-A...

[justjohn]

I will attempt an in depth when I eventually get an mpguino. Might be a little while though.

[actwithclarity]

Lol. 2 days ago before I left town (in a different vehicle), the fuel gauge was almost at empty, so I had "fill up tank" on list of things to do. I was having nightmares of 25mpg on my geo metro.

Today when I started up it was showing just below half full. O_o After flopping back and forth during my errands, it was like 1/4 full when I stopped at the same pump that I used last time. Turns out the official number was 48 mpg which I can't complain about for learning to drive standard and hence purposely forgoing any hypermiling techniques. Extra loving my car already, but I think the fuel gauge will drive me crazy.

Still wish I knew how to use these BSFC charts to my advantage.

[PaleMelanesian]

Here's how I interpret the BSFC charts. If you're on the gas, put it in the efficient zone. Approximately 1500-2200 rpm and ~75% throttle. In most cases that makes you accelerate. So you hold that zone until reaching the upper speed limit (either legal or self-imposed). Then go to neutral and coast for a while. I do engine-off coast which saves even more fuel. Then get back in gear (bump-start if EOC) and do another pulse. Repeat repeat repeat...

I find slightly better results at lower rpm - centered at 1700 or so - instead of the 2000+ the charts usually show.

[euromodder]

48mpg is a good start.
But it certainly can be improved upon.

Forget about the fuel meter if it's not working properly.
You know how much fuel it's using, you now how much fuel goes in, and you know how far it's gone since refueling - that's all you really need to know

The low-fuel light might still be useful though.

[actwithclarity]

Originally Posted by PaleMelanesian

Here's how I interpret the BSFC charts. If you're on the gas, put it in the efficient zone. Approximately 1500-2200 rpm and ~75% throttle. In most cases that makes you accelerate. So you hold that zone until reaching the upper speed limit (either legal or self-imposed). Then go to neutral and coast for a while. I do engine-off coast which saves even more fuel. Then get back in gear (bump-start if EOC) and do another pulse. Repeat repeat repeat...

I find slightly better results at lower rpm - centered at 1700 or so - instead of the 2000+ the charts usually show.

The chart I linked seems to show 3000 RPM as the best?

I don't understand, if I am at 3000 RPM, how do I know if I am at 25, 50, or 80 torque?

[actwithclarity]

Originally Posted by euromodder

48mpg is a good start.
But it certainly can be improved upon.

Unfortunately I'm still not sure of how fast to rev and shift gears for best efficiency but my next tank will probably be significantly better since I was driving slower, not speeding in general, and driving without breaks for all my trips today.

I think P&G is something I will never bother with.. to much work and boring. EOC I haven't tried yet, just coast in neutral so far, seems like a pain to turn engine on and off without a start button and have music cutting in and out.

I am thinking to test a new hypermiling technique: getting out at stops and pushing the car fast enough so I can skip 1st gear entirely. Just won't work going uphill.

[euromodder]

Originally Posted by actwithclarity

The chart I linked seems to show 3000 RPM as the best?

It shows good BSFC within that 283 line, which outlines a whole area from 1500rpm up.
I'd say you're OK from 2000-2500 at 70-85% load, so try accelerating in that area and see what results that gives.
If it still works, try shifting even earlier.

Aiming for the small 250 g/kwh window itself during acceleration seems futile.

Remember :
While you may get good BSFC, i.e. good power / gallon, you still get lousy mileage, so try to switch to steady driving (or P&G) as quickly as possible.

I don't understand, if I am at 3000 RPM, how do I know if I am at 25, 50, or 80 torque?

You don't really know, though you could try to relate it to the % loading of the engine (LOD gauge if you have a ScanGauge).
Gets complicated fast though, as it varies with rpm.