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My father has a new Cadillac that gets 28 on the highway with a v8. However the gas mileage comparison between what an engine gets in a lighter and much more aerodynamic car has nothing to do with what that set up will get in one of these old trucks. My father also has a '91 f150 with a 302 and AOD trans that gets 18-19 mpg. That same set up in my 69 F100 would probably not get over 15 mpg. If you lighten and lower the truck it will help. Lowering may be the best thing.
If I was in your boat, I'd take a hard look at the specs on the 1st generation F150 Lightenings.
That is about the best real world use of power and economy in a 'truck' package I can think of... that has proven itself.
I would add electric fan, 1-5/8" ceramic coated long tubes, 2-1/2" dual exhaust... and call it a day.
I would expect to loose 2-3mpg swapping the drivetrain into a heavier loaf of bread.
And, I too will sing the praises of the EFI 302 mustang package.
Mine routinely knocked down over 25mpg(much closer to 30 actually) but keep in mind that is in a ~3000lb 'aero' nosed car.
if you want to go the route of the 300, this is what i would personally recommend:
offenhauser 4v intake with 390 4v holley
port and polished intake and exhaust
RV cam
EFI exhaust manifolds with dual 2.25 exhaust w/ H pipe
pertronix ignition
mazda 5spd OD
3.00 gears
aluminum driveshaft
race weight hood and fenders
this should yield roughly between 200-250 hp and 300-350ft/lbs and weigh in at around 3700-3800lbs maybe a little less, and get about 17-21mpg.
i rebuilt a 69 windsor for my 72 long box and with a mild rv cam and holley street avenger it does about 280 miles to the tank and the engine stock had 280 horse and 390 pounds of torque i believe
I was just wandering earlier today while driving my Mack down the road at 70 with the engine screaming at the tone of 2000 of 2100 RPM, if a diesel is most effecient near red line, where would I need to build and gear this truck to run?
My current truck has the same set-up as the old one, less the engine makes 20 more horses at 300 more RPM. Mack geared them both to redline around 80, and even though the newer truck runs at a much higher engine speed, it is more effecient.
Should I rethink my gearing and go for a 2300/2800 RPM set up and run a RV cam in a smaller engine? Maybe 2500/3200 RPM and an 600-4800 RPM camshaft in the current 302? Thats the smallest XE cam CompCams grinds.
my door tag is not legible, so what DO these trucks weigh? I was going to put this truck on a diet anyway, so who has the best selection of glass body parts? If I keep the 3 spd, what should I expect from a Gear Venders Overdrive unit (3+2=6 forward, 2 reverse)?
usbody.com has the best and i think the only fiberglass parts for 67-72 Ford trucks. They are not cheap, but you benefit greatly from weight reductions. put a small v8 or inline six in and you will still keep a light weight truck. try to find aluminum engine parts such as intakes, heads or waterpumps, to lighten the engine some. lower your truck 2 inches in the front and back and that should yield better mileage, aerodynamics, and give it somewhat of a performance look. Try to lower your horsepower to weight ratio without really modifying the motor and get a lot of weight reductions to lower the power to weight ratio, as that will increase gas mileage and acceleration. it would be like the difference between a 302 in a truck versus a mustang.
The part about the Mack was it made me wonder if more revs would help the mileage? I thought less revs would yield better mileage, then I got to thinking about more power-less throttle at higher revs. I remembered Friday morning, that my best friends ranger always got better mileage. They were both 96 Ranger XLTs, 2.3 5 spd, 225/70R14s, the only difference in the trucks was the rears, mine has a 3.08, his had a 4.10L. I was always about 18-21, he stayed at 23-25. The other difference was I kept it in the 2-3k range, he shifted at 4k, and didnt run OD until 60.
A lot has to do with the engine. I think the engine that you are referring to is a dog plain & simple. I gave one away with that engine because it was so gutless. The engine absolutly had no power, so it needs rpms to make some. When it lugging around it aint getting mpgs.
Take a forum correct topic like a 70 model with a 390 V8 and a 300 I-6. The 300 while a torqueie motor has to have some gears to make it have power. You bout have to run 375 or higher gears to make it work well. The 390 on the other hand can make great power with a 3.00 rear.
The FE needs to turn low rpms to get mpg & the I-6 will have to turn a little more to be effecient.