Technically correct methods for improving mileage
 

Lets start the thread with methods that cost nothing.
Tires: we have to buy them some time
* the narrower the tire in general the better for mileage, less wind resistance
* the higher the tire pressure in gen. the better mileage, less tire deflection
* the more shallow the tread better MPG, less squirm, and therefore less heat
* the taller the tire better MPG, changes the engine to ground ratio, also changes ride height, now we must deal with more air going under the truck.
** don't forget anything that changes the rolling circumference of the tire makes rechecking the odometer manditory.
* the cooler the tire runs, the less rolling resistance it is producing. Tire makers are now rating some tires for rolling resistance.

To sum: The more a tire looks like a racing bicycle tire the more MPG's.

Would someone like to take lubricants next? I'll get to engines eventually.

That is BS. By this token I could put on a 50" tire and get better mpg than what I'm getting with a 31" right now.

There is an optimum ratio (combined from gear ratio and tire size) that will provides the best mpg at a given speed, and any change in the raio in either direction will lead to a decreased mpg.

good point help separate the BS from the scientific
 

Correct, to be more specfic there is only one 'best mileage' RPM and Load for a given engine. Usually around max. torque peak. It would follow then that for each job there is only one best engine size. I qualified by asking how did can one handle the change in frontal area and ride height. I can't blame the 50" tire because the under carriage of a truck is aerodynamically inefficient. I started with tires because I am reading a lot of inconsistency on the subject. As we address each subcomponent, I agree we must keep in mind how the total system will come together in the end. We will even need to address the reasons for speed limits in the end. Whats BS is anyone who thinks these energy problems are going to go away. I digress.

why does one engine get better mileage than another
 

In general:
*the higher the compression ratio the better mileage, up to about 22 to 1 NA, some mills get this same effect with a compressor. Present gasoline engines probably can't take full advantage of ethanol at 10to1, better at 12or14 to 1
*the fewer number of cylinders the better, less fiction
*the more BTU's per gallon the better, diesel at approx. 130K vs. LPG at 91K
*the Fuel Injected engine usually is better, closer control over air/fuel ratio
*the smaller engine gets better MPG, if its running near its max. torque peak.
thus if the job requires 50 Lb-ft of torque @ 2500 RPM and a certain 50 cu. in. engine's max. torque is 50 Lb-ft @ 2500, it would get better mileage than a 100 cu. engine operating at 50 Lb-ft.
*the longer the stroke, the more torque per cu.in., the lower (RPM) the torque peak, the less fiction, computer controlled engines have offset much of this advantage, because they can be lugged down without as much chance of mechanical damage. The old 2 cylinder tractors held the fuel economy records (for tractors) until recently.
To sum: the smallest, slowest speed, turbo'd, diesel, 3cyl, that can just make enough torque to propel the load on level ground will get the best MPG.
What about hills you say, that's the FORCE made transmissions.

A turbocharged engine is also more efficient because it extracts waste heat energy from the exhaust and converts it to "free" extra compression.

The most efficient gasoline engines ever produced (in hp per hr per lb of fuel) were the 1950's Curtiss-Wright 3350ci 18 cylinder aircraft engines. They had something even better than turbocharging, turbocompound, that converted exhaust heat directly into power fed back to the crankshaft.

Jim

3350 cu. in. / 18 cyl.= 186 cu. in per cyl.
*Big cylinders, long stroke, slow turning, very efficient.
The Deere engine I'm thinking of had 189 cu. in. per cylinder and a rated speed of 1250 R.P.M.
Long stroke = long burn time
Having a turbo is almost like being able to vary the compression ratio.
Now if we could vary the displacement to fit the Load, with the engine always running at peak torque, we could gain efficiency. Brand X company is half way there by cutting out 4 cylinders when not needed. How 'bout it tuners, I challenge you to do it on a Ford. They deactivate 1,4,6,7 by allowing the lifters to collapse and cutting out the injectors. Forget the phase in/out, just give me a rocker switch that will do that.

what driving technics can save fuel
 

I easiest way I can describe how to save fuel is:
*practice driving as if you have no brakes.
Try not to use engine braking also.
One can pop the tranny into neutral and coast with the engine idling. Be safe.
The point is the further you drive ahead, the more you can save.
Because aero-drag increases exponentially with speed the best mileage is often just above the speed where the tranny stays locked up in high gear.
Keep in mind that overdrive is great as long as the converter stays locked.
If the load unlocks the converter in overdrive, then you may gain efficiency by going to direct drive locked converter. Two reasons for this the tranny gear train is often more efficient in directdrive and when the converter unlocks you lose some of what you gained with overdrive.
On my wish list are changes with the factory cruise controls, there has got to be a better way. When the + is pushed the vehicle should accelerate at the most efficient rate, not unlock the converter or down shift. Also tuners, I would like to be able chose a wider band width at a set speed. For example, Allow the car to go 60 down hill and 50 uphill if the operator choses. Cruise control should strive to keep the engine in closed loop.

The odd thing is that aircaft engines are short stroke, compared to the bore, but it is still a long distance in automotive terms. They do run a lot of spark advance, which extends burn time along with the low rpm. Rpm was regulated constant using a propeller governor, at any power setting. Throttle was used to regulate manifold pressure, hence power, not rpm.

Doesn't the Curtiss-Wright have over a 6 inch stoke? About 6 X 6.

I had a thought, could a tubocharged engine be programed to vary boost based on the percent ethanol present? If so why don't the E85 engines have it?

Lubricants:
*thinner oil generally is more efficient.
Thicker oil in an engine generally operates at a higher temperature than thin oil.
Thicker oil protects the bearings better than thinner oil on start up. But thicker oil may take longer to build pressure on startup. So thicker oil is a bit of a catch 22. Is film strength more important or is efficiency more important. In general, run thinner oil in new engines and thicker oil in engines that have more bearing clearance. I have run John Deere Hygard in a manual transaxle designed for 90W with no apparent problems so far. I don't how thin is too thin.

Which drive train is more efficient in high gear, everything else being equal?

A 4 spd manual (4th direct) and a 3 to 1 rear.

Or a 6 spd manual (6th @.75) and a 4 to 1 rear.

Ans. The 4 spd and 3 to 1. Why? Because the power flow through the 4 spd in direct goes through no gears. Every time power is transmitted through gears or chain it loses a little energy. A direct shaft is generally more efficient.