Best rpm to shift at?

[darkspork]

I hope there isn't a threat already dedicated to this, if there is I couldn't find it.
What's the best rpm to shift at (for fuel efficiency) with the SOHC 4.0? When I first got the truck I was shifting at 2000 and read somewhere that on this engine 2500 is much better, so I switched to shifting at 2500 rpm. As of now I'm having a hard time beating 17mpg in mixed (perhaps 80% highway) driving. I changed the fuel filter, air filter, rotate and balanced the tires, keep my oil clean and the truck is generally well tuned up. Best I've got in the truck is 20.2mpg doing 100% highway driving on winter blend gas.

The truck runs well I was just hoping I could get over 17mpg (I understand its a truck with an inefficient engine). Anyhow, what's the best speed to shift at for best gas mileage with my truck? 4.10 gears, 5 speed manual, shift-on-the-fly 4x4, 4.0L SOHC...

 

[darkspork]

I didn't see that a mod already made a sticky for this. I feel kind of stupid, sorry. Somebody go ahead and delete this thread.

 

[AllanD]

That post up there s great isn't it?

 

[darkspork]

That post up there s great isn't it?

Yes, I just don't fully understand it. I understand how a vehicle operates. I know what torque and horsepower is, I just can't seem to relate to chart to best shift points for gas mileage. Is it when the engine first hits its peak torque(looks like its 2800 rpm on the OHV engine based on the chart, I think its 3000 on my OHC)? I suppose 17 isn't too bad for a truck though.

 

[AllanD]

For mileage? you are probably trying to overthink the problem.

Rules for economy:
1)Maximize tire pressure, higher is better because the less the tire deflects
the less energy goes into heating the tire sidewalls.

2)AVOID LIKE AIDS using full throttle, the engine at WOT goes into "open loop"
and in general open loop operation causes the engine to run rich.
Running "rich" wastes fuel.

3)Upshift at any point you feel comfortable but THE thing is to drop the engine to
a point above a minimum rpm in the next gear. Generaly above 1800-2000 for a 4.0.

4)avoid abrubt increases in throttle position suddenly "snapping" the throttle from
20% to 80% is almost as bas as using 100% throttle.

5)And finally avoid cruising above 2300-2400rpm.

The 4.0 becomes more piggy

the beautiful thing about the 4.0 is that for low rpm operation it
just doesn't care what rpm it's running at... the only thing is that
at lower rpm while you have the torque you don't have the power
so if you downshift and use more rpm in a lower gear you'll spend
less TIME accelerating and somethimes that's preferable, because
less time accelerating means more time in your more efficient cruise mode.

but there is one caveat about low rpm operation.
The oil pump doesn't reach it's maximum capability until 1800-1900rpm
so I don't like running my engine under load (cruise is ok but accelerating isn't)
below 1900 or so... remember the oil pump keeps pieces from banging
against each other.

Maximizing efficiency has some factors that seem counter-intuative

Like don't be pathalogical about maintaining a precise speed on long highway runs... for downhill runs let the speed build particularly when there's another hill you have to go UP on the other side....

Try running your A/C full blast on downhill runs, it improves engine braking (using the brakes pisses away energy) and turning it off on upgrades.

Running the A/C on a steep downgrade is basically "free"
because you already paid for that energy climbing the hill in the first place, using the brakes is "giving" the energy back

NOT using your A/C like this is like getting $100 from the ATM to
buy something, only spending $85 then simply giving the money back to the bank (NOT depositing it, just dropping it through the mail slot)

And incase you forgot brake pads and rotors cost money too...



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