I guess it could be done, but not sure it would help much. Case in point, years ago I replaced my gas hog 350 in a 75 full time 4x4 Blazer with a 283....it was even a 2bbl, thinking it would get better mileage. It didn't, engine just had to work harder. Now, with the EFI, you may have a better shot at it.

The Toyota camper is probably lighter than your van.

 

Yeah, I thought so, I once had a friend with a Ford f 350 flatbed, and he would haul three words of wood in it and still get 13 MPG. The secret, a 300 straight six engine paired with a manual transmission and stock carb. The truck could only reach speeds of 60 mph, still, that's pretty good for that engine and vehicle combo.

 

the chevy 6 does not get as good of fuel economy as the V-8 based on bsfc. The more power you use to accelerate or climb hills will burn more fuel.
If you build an engine for fuel economy you start with how much power you need and find the engine displacement that best matches all the parameters,,,
rpm that the peak torque occurs and where that will be in your transmission/rear gear system. getting rid of parasitic drag and hp losses.Some heads have better combustion chambers

 

Yeah, I have no idea where to start with doing something like that. Do you or anyone else have some pointers.

 

The six was factory available in the 1970s vans. This is a bolt-in swap.

The question you need to ask yourself is, how many hundred thousand miles will you have to drive to make up the cost of the swap in gas savings? And even if you think you have to do this, a modern LS will bet much better mileage than a 250 or 292, especially since your cobbled EFI won't have the benefit of factory engineering. Also keep in mind that the van has all the aerodynamics of a shoe box. No matter what engine you put in it, it's not going to win any economy awards.

 

Its tough to improve mileage on a box boxy van, since you can't really improve the aerodynamics. GM makes a good 6 cylinder engine, but for this application its probably not worth the trouble and cost compared to an SBC.

If you want to save money overall, I think I would just look for a 305 and then use the best tuned stock EFI you can find. A TBI system would be an inexpensive choice, and they are very easy to find and work with. GM has better EFI systems, but the price goes up and they get more complicated. Then use a 700R4 overdrive and a rear end ratio that puts it into the rpm range you want for highway use (probably in the range of about 2000-2200 rpm at 70 mph).

Bruce

 

There's a massive difference in what engines and vehicle combinations such as the Chinook are rated at compared to what they actually produce, the ratings being much higher than real life. For any highway object the aerodynamic and rolling resistance of driveline, bearing, brake drag, and tire losses are an X amount that is variable directly with speed, more speed requires more power. Regardless of engine size this takes X amount of power. For a small engine that means it's working harder into its design strength limits which reduces its life span against a larger engine not working as hard into its strength limit. As far as gas mileage goes it is easy to get worse mileage with a smaller engine as the greater power extraction against its size requires a power rich fuel mixture to keep the combustion temps down below the detonation limit. Much of this is variable to environment if you live in hilly to mountainous country it's worse because the gravity loads are higher than if you live in flat country. Also the faster you drive the worse it gets because of the multiple drag issues with speed.

Then you get to design efficiency of engines, inline sixes tend to have very poor intake systems which for the most part is simply imposed be engine length meeting cheap to produce manifold systems. The American manufactures spend a lot more money on V8 designs than I6 designs not to mention the V8 is a more robust design for the material weight used and for induction is simpler to make efficient and effective. But the tune configuration on the V8 greatly affects its mileage.

That last statement in the context of effective mileage solutions against relatively simple design solutions get you to the 1987 through 1995 LO3 and LO5 V8's. The LO3 being a 305 and the LO5 a 350. These are the Swirl Port headed engines that use a 2 bbl Throttle Body Injection (TBI) with very mild cam's. These engines use an overdrive transmission either 4 speed automatic or 5 speed manual with a deep low for getting started without so much throttle tip in and overdrive for highway cruise in top gear.

For an existing 350 the mild cam (milder than any other GM cam) which is a flat hydraulic can be installed and the Swirl Port heads interchange. Or the entire long block can be had as a crate motor. The factory TBI is a pain as it is designed to be EPA compliant so the rocket science is far in excess of what is needed for the job at hand. But fuel injection is attractive as it is more efficient than a carb. The answer here is aftermarket Self Learning TBI which is more expensive than a carb but is simple to install.

This type 305 or 350 combined with a properly sized for the power truck 5 speed stick or a nicely built 700R4/4L60 (no E after 4L60 as these need a computer to operate) delivers a 4 speed deep low high overdrive automatic.

This will be as good as it gets for best mileage at least up front investment that still has the power to get over a hill the same day you start up it and doesn't eat you out of house and home doing it.

Bogie

 

What Bogie said.. You could consider a swap to a late model computer controlled engine and trans should you be up for doing that. the modern engines have much better designs and fuel management programs..

Sam