Inliners International Forums General Discussion Engines Questions of fuel mileage.

I have an 82 chevy truck with a 250 inline 6 and was wandering what would be good to do to give it more fuel mileage. I am going to add an electric fan and I was thinking of upgrading the ignition system with performance coil and wires. I think the coils are the same for the v8 engines, but would like to be sure and you can buy custom wires if necessary. I want to get more power and torque, (mainly torque) but I don't want to move the power band up in the rpm range too much if I don't have to and I have seen the split headers for dual exhaust and my truck already has a split manifold with duals, so I thought that might be good for mileage and power, but am afraid that it might move the torque up the rpm range.

Since your truck is an '82 it will already have HEI installed. If the stock plug wires are in good condition its unlikely to see any gain by changing just the wires. A performance coil and wires will help a bit. MSD has a multi-spark ignition module that fits inside the HEI dist. Where you will notice a difference is at idle and cruise.

If you really want to pickup mileage then the next 2 steps that will help is:

1) installing an overdrive transmission
2) installing TBI fuel injection

But both of these invlove more $$$ and at the end of the day its upto you to decide if the extra parts are worth the expense or just pay at the pump. With the OD and TBI you can expect a 15-25% increase in fuel milage.

For increased fuel economy, this website might help:

http://www.thecarburetorshop.com/Troubleshooting.htm#Fueleconomy

Jon.

The fuel economy tips in the carbking's excellent link need to followed by all of us. However, there was one that may need a little discussion: "Adjust your driving habits. Everyone knows that full throttle acceleration wastes fuel, so we will not discuss this." Let us disscuss it.

Full throttle acceleration may actually save fuel. A few years ago (to someone my age 1985 is just a few years ago) Car and Driver reported on some road tests conducted by BMW that fairly convincingly showed that full throttle acceleration could increase mpg over a simulated city driving scenario by somewhere between 10 to 25 percent. As I recall (I seem to have misfiled the article) BMW measured about 20 mpg with full throttle acceleration from zero to about 30 mph and about 16 mpg with quarter throttle acceleration. With either throttle setting, better MPG was obtained by shifting at 2000 rpm than at 4500 rpm. This is also one of the reasons why better mpg can be obtained with a manual transmission, as the driver can independently control both the throttle and the transmission gear selection. Some automatics do allow the driver to control the shift points. Otherwise, full throttle acceleration results in lots of rpm and pumping losses.

The first article where I read about the advantage of full throttle acceleration was in Motor Trend, June 1956. In this report, they averaged about 20 mpg at an average of 30 mph average trip following the recommended “drive like an egg is between your foot and the pedal”. Then, they used the “burn and coast” technique, where they accelerated at full throttle, in high gear, up to about 40 mph, and then coasted, in neutral with the engine off, down to about 10 mph, restarted the engine by popping the clutch in high gear, and repeating the cycle as required to get to the end of course. This resulted in 42 mpg. Admittedly, this might be tricky in heavy traffic, as all of the drivers would need to get their burns and coasts in phase to from having a few bumper touches. I’ve been told that this burn and coast technique has been used in the super-economy trials where several hundred mpg is achieved.

This may seem to be counter-intuitive, but if one works through the physics (engine efficiency vs. rpm and manifold pressure, F=ma, V= at, D=CdqS, E=mv^2/2 etc.) of the acceleration and steady speed of a car it will become apparent. I convinced my son to try a modified version of the burn and coast technique driving between St. Louis and his school in Springfield MO in his S-10, with an inline four. On one leg he measured 34 mpg compared to the 27 mpg with a normal steady speed, averaging about 65 mph both methods, driving the same direction.
I’ve been looking for a controlled test that shows that part throttle is better than full throttle for mpg, but I cannot find one. Of course, if you engine has so much torque that it smokes the tires at or near full throttle, you may need to back off or get a taller gear. That is real secret – drive at nearly full throttle with the rpm in the range for near-peak torque. This requires a multi-speed (or CVT) with a very wide range of ratios.

The Hypermilers (the people into competitive driving for fuel economy) also reccomend turning the engine off at stoplights, or anywhere else you would have to idle for more than a very few seconds. As well as drafting (well not that close, but the same idea) and the coast up to a stop is a big one too (with the engine idling, in neutral or off). Also, try to park where you don't have to back up, they consider reverse wasted motion.

This is all predicated on late model tight clearance (with as light an oil as possible) EFI equipped vehicle though, so with a carb (and larger clearances / heavier oil), I would probably tone down the don't let it warm up, just accellerate slowly while it's cold plan.

I'm not one myself, but I read all this in an article in Popular Mechanics recently IIRC.

I found some more stuff at:

http://www.hypermiling.com/car-mpg.html

All this talk about fuel economy dredged up a dusty, cobweb-covered memory from my formative years in the 50's and 60's. Whatever DID happen to the Mobil Economy Run, anyway?

I remember reading a blurb about that in Auto Week (IIRC) a few years ago. They quit running it and some people have tried to reorganise it over the years without much success.

I have a question: When coasting to a stop does it make a difference in mileage if you let the (manual) transmission "slow" the car down as opposed to taking it out of gear and applying your brakes?

Martin,

It seems as if the lowest fuel consumption would be obtained by timing the coast, with the transmission in neutral and the engine off, so that the car came to a stop at the desired spot with no engine or wheel brake application, so that very little of the energy that went in to accelerating the car went up in heat. Easier said than done. It seems that using the brakes, either with the engine off or idling in neutral, would use less fuel than using the engine as a brake with the throttles closed. The hard manifold vacuum with the engine rotating above idle speed will probably pull more fuel through the idle fuel ports than would flow at idle speed.

Back in the late '50s, I was considering buying an English Ford Anglia from an old man (I'm about his age, now!)

I asked him if the car got good mileage.

His response was............."Why son, this car gets such good mileage, you'll have to stop every 20 miles, or so, and drain some out!"

I didn't buy the car.......too much trouble, doing all that stopping and draining.

Thanks efi-diy, do you have more information on the price of an efi system, or know where to get info? It does have the HEI already and a reply I got from another of my postings said that the coils for the V8 and 6 are the same. I was thinking of maybe putting a six speed transmission, but I don't know how much trouble that would be. Does the inline 6 have the same bellhousing bolt pattern as the v8? I appreciate any help or suggestions.