A little Scan-II advice please.....

[Hip001]

I'm watching the instant and avg mpg on the scan-II. I noticed this morning that in 5th gear almost lugging the motor is when I'm getting the most mpg. Just my conceptial thinking but it seems to me the car would be more efficient if i down shifted and ran a lil higher rpm without lugging it. According to the SGII, lugging it in 5th gear had higher mpg's. So I was in 5th gear doing 40mph with the SGII instant mpg in the upper40's.

[SentraSE-R]

Believe your Scangauge. Lower gear/faster acceleration may bring you up to speed faster, but it uses more fuel maintaining that speed than higher gears do.

[CigaR007]

But which would be better (most efficient), a short acceleration burst in lower gear vs a long acceleration in 5th gear ?

[SentraSE-R]

It depends on your engine/transmission combo + engine load. In my personal experience there's not much difference with my MTs. A shorter fuel intense burst in third or fourth gear uses about the same amount of fuel as a lengthier leisurely acceleration in fifth gear.

Lighter load/slower acceleration seems to work better with my family's ATs.

[NeilBlanchard]

It depends on the load -- low up slopes work great in 5th with light throttle, but I think that it may be the throttle position that matters? On steeper hills, then lower gears for shorter times works better, in my experience.

Have you had the ScanGauge II long enough to calibrate it? Say, 3 or 5 tankfuls, at least?

[some_other_dave]

Look up the BSFC charts elsewhere on this forum. You'll see that ~80% load around 2000 RPM is pretty close to the most efficient way to accelerate with most engines. But for steady-state driving on a flat level road, the best economy is attained "as slow as you can stand to go in your highest gear without lugging too badly". Add "with the torque converter locked" if you have an automatic transmission.

-soD

[Hip001]

interesting stuff! I'm now watching my SGII and seeing what I can average each morning on my 45min drive to work. 54.4mpg is my highest so far. Pulse and glide and slow 5th gear speeds seem to be the trend for higher mpg.

[99metro]

Don't confuse "fuel efficiency" with "fuel economy".

Generally the best fuel economy is just after the last gear shifts in an automatic with light throttle... and somewhere in the general vicinity of 1000-1500 rpm in the last gear of a manual transmission. Give or take.

Fuel efficiency varies greatly engine to engine, but somewhere in the peak torque and peak horsepower range the engine is more efficient assuming it has about 80%-ish load on it. Mostly this isn't where it uses the least amount of fuel.

[Hip001]

[QUOTE=99metro;235829]Don't confuse "fuel efficiency" with "fuel economy".

Generally the best fuel economy is just after the last gear shifts in an automatic with light throttle... and somewhere in the general vicinity of 1000-1500 rpm in the last gear of a manual transmission. Give or take.QUOTE]

Ok I am confused now :-) Effeciency or economy? All I know is to watch the instant reading trying to keep the avg mpg numbers as high as possible.

Is economy miles/gallons=mpg
and efficiency is how much it's using at any given time to maintain X speed?

[99metro]

Economy = MPG
Efficiency = BSFC Charts.
Brake specific fuel consumption - Wikipedia, the free encyclopedia

While accelerating, you want efficiency. 75 to 80% throttle if you have electronic fuel injection (most modern vehicles). My opinion is that if you have more than 3 or 4 miles between stops, then do 75-80%. Anything less than that or if you are city driving, then slow acceleration is best. Overall, this will net you the best fuel economy.

You still want the best fuel economy (MPG). You have to learn and practice some hypermiling techniques.
Example: You should accelerate on the downhills and avoid increasing speed on the uphills - it takes less horsepower and less fuel that way.
Example: use a steady throttle, not steady speed - allow the vehicle to speed up and slow down in hilly areas while maintaining a steady "TPS" or Throttle Position Sensor.

There are always lots of "discussions" about efficiency and economy. If you put a high load on the engine (such as accelerating, getting the load moving up to speed), you want engine efficiency. When you get the load up to speed, you want economy, or the least amount of fuel to keep it moving. Road conditions, weather, wind speed/direction, vehicle/engine health, fuel quality, driving technique, etc all play a part of getting the best economy.

That Scangauge II will teach you lots of stuff. Ecomodder.com folks (and the articles here) will teach you lots of stuff. And you will see where your vehicle nets you the best fuel economy (MPGs) and at what speed and at what RPM. If you can find folks with the same vehicle they can really help you attain the best MPGs. Have fun!