Hi, folks.

I have a 74 2wd with a 390 and C6 trans. Engine is stock, but bored .030, factory 2bbl rebuilt. Trans has a mild shift kit. Both have about 25000 miles. I drive only a few thousand miles a year (less than 5000), the vast majority in town. My average fuel mileage last year was 9mpg. I realize with an FE bigblock, that's probably about right.

Now that fuel here is nearing $2/gal, I'm wondering the best line of attack to get a few more miles per gallon. Plugs, cap and all only have 3000 on them, oil is changed regularly, no black smoke in the exhaust (dual 2 1/4"), carb is okay, though accelerator pump is not perfect (little hesitation on accel. when cold). Cooling system is all new with 180 degree t'stat.

Should I start by leaning the carb out some more? I know that headers are a bit of a help, but I also have been told several times that headers for this truck will have to be removed to replace the starter, which seems like poor design and lots of wasted time. Change to a 4bbl intake and carb?

The other thing I'm thinking, since this is my daily driver and I will keep my 4X4 a big-block, is to find a donor truck and swap a 302 in place of the 390. I've heard good things about the 300 six-banger, too. I'm guessing I'll have to change transmissions, too, but if I find a donor truck, that will all be there. Front springs seem to be the same for all V8s, but what about raditor (bigger is better for cooling, so I am guessing I could leave the original, but shroud might be a problem....), power steering pump, brakes (not power, so I think no changes), shifter.....

I'd really like to see this truck getting 15mpg or better, but that might not be realistic. By going with a 302, I know that parts would not be a problem, could even change to fuel injection pretty easily, which would really improve mileage.

Anyone with a 302 or 300 in a mid-70's F-series? What kind of mileage do you get? What transmissions (auto) work on these engines.

This truck will not have to do major or prolonged towing or hauling, just a run-around type, some road trips, going to work, etc. Any help anyone can offer would be great.

Thanks.

Matt

 

The 300 and 302 get about 15 mpg average with a 4 speed auto, some get more some get less. Now a engine and transmission swap will cost you probably around 1000. Lets say you drive 5000 miles per year and get 10 miles per gallon, that's 500 gallons of gas and roughly about 1000 bucks, ouch. Now 15 miles per gallon would roughly cost you about $650.

That's a $350 difference, it would take 3 years to get your moneys worth. Not too bad. Have you thought about getting like a little POS car that gets 30 MPG?

 

my 302, C4, 2.75 gets 9 city.

 

My 300-6 in an E150 Club Wagon with AOD got 17mpg highway and 15+ city. A 302 in the same vehicle got far worse mileage. A 302 is a poor choice of engine for a heavy vehicle. It would take a long time to pay for the expense of an engine change with gas savings.

p.s. The E150 with 300-6 was rated 14mpg highway but it had special modifications (no damn computer).

 

Matt, I wouldn't do it. A 302 or a 300 will have to work awfully hard to move your truck around. It might get the same mileage or maybe a bit worse. I have a '71 2wd with a 390, 4 barrel and a 428CJ intake and C6 and 3.5 gears. This truck also has a biggish Crane cam gets driven 'enthusiasticly'. It is giving about 10-12 miles per gallon. I wonder a couple of things, how tall are the tires you have in the back ? What ratio are your axle gears ? What kind of ignition does your truck have ? If you still have points, a healthy Duraspark or Pertronix will let you tune it somewhat leaner for a bit better mileage. Do you know what pistons are in the rebuilt 390 ? If you have the low compression pistons most rebuilders use on truck engines, more compression would give better economy. Are you willing to swap the pistons ? Where in Kansas do you live ? A lot of places in the plains states sell a fuel called E85, frequently for 50 cents less per gallon than regular, and setting upm your truck to run it wouldn't be that hard. DF, @ his dad's house

 

Hi, Dino.

Tires are LT235/75R15's on all four corners (factory tire size, or at least as close as I can get 30 years later). Axel ratio is 3.00, so that's reasonable for highway (70mph is about 2800-3000 RPM). Ignition is the original Ford breakerless type (replaced 25000 miles ago when rebuilt). From another post I've made, I'm planning on setting the timing (currently about 6 BTDC) to 10-12 BTDC per FAQ advice. Pistons, don't know. The builder does a lot of race engines, but I was a poor college student at the time, so I went pretty stock. I would imagine they are whatever standard pistons come in a master rebuild kit. I doubt I'd swap pistons until I had to do something else major, but I'll keep that in mind for my 4X4 build that is somewhat pending (thanks for the tip). I live in SE Kansas, and I haven't seen E85 anywhere around here. But I like the idea of it, just as I like the idea of biodiesel (I'm all for renewable/fast growth resources). Maybe before long..... I'm also giving serious thought (and have been even before this) to changing all the lubes (oil, trans, axel, ps, etc) to Royal Purple products. I know, it's not a big mileage gain, but all the info I've read on their product line points towards good things in terms of wear protection, stability, etc. And I just like the name. As someone else on here said, you've got to love a company that markets a product called "Royal Flush" (or at least used to).

I really don't want to part with the bigblock. Has come in handy many times. I doubt I'd save enough in fuel to justify the price and time to swap engines, anyhow.

Looks like it's time to do some basic tune-up and see what happens.