the f100 i just picked up is geared stupidly low. i wana be able to cruise down the road at 65mph turning about 2k rpm. i figure that would be about optimal considering i wont be towing anything ever with this truck.

it has 4.10 rear end ratio 26" rear tires and a non OD trans. that puts me at 38mph in 3rd at 2k rpm....not exactly ideal.

i just picked up a set of 28 inch tall tires so that would bring it up to 41mph at 2k.... still not good

it has a c4 currently but im pulling that out and replacing it with either a zf5 or a M5OD 5 speed. both have ODs around .75 just changing that brings me to 54mph in over drive....getting better but still a bit low.

now i have a 78 f150 with axle code "13a" on the stamped vin. from what i can come up with that should have a 2.75 rear end ratio... pretty tall.

when i punch that into the calculator witht he OD trans it puts me at 81mph at 2k.....too fast?

heres my question, do you guys think id get better mileage with the 2.75 ratio or the 4.10? i personally think both suck and i was hoping the parts truck would have some 3.55s in it or somewhere close to that. with the 4.10s it takes about 2600 rpm to get to 65. with the 2.75 it takes about 1600 rpm to get to 60.

i think it would be bogging with 275s and "over revving" with the 4.10s at 65mph. im just trying to work with what i have so if you had to pick one which would it be?

im getting my numbers from here, obviously its not 100% accurate when you are driving something as aerodynamic as a brick but it gives you a rough idea.

 

If you're never going to tow then I'd go with the 2.75. Spruce up the motor a bit and that'll help the bog. It'll at least do for now until you can find some middle ground. Kinda at opposite ends of the spectrum. lol

 

well the motor is a mild 289. heres the supposed spec from the PO

289 bored .030 over
world heads, not sure exact model
roller rockers
edelbrock air gap intake
cam, not sure the exact one but it has a little lope at idle
holly 4bbl, dont know cfm
some sort of LT headers

she runs pretty good so she might have enough push.

i hear ya about opposite ends, i was hoping my parts truck would be in the middle but no such luck

 

I originally had 2.75 gears. I have a 302 and 31" tires. The 2.75s are great on the freeway. It'll loaf along at 75 easy. With those gears, it'll drive like a 4 speed automatic overdrive, with no 1st gear. Floor it from a stop and it just kind of rolls off the line. If you need to pass someone, it'll need to kick down.

I put in 3.50 gears. It gives it a nice kick off the line, and the 302 doesn't mind spinning at freeway speeds(your 289 would obviously be similar). That wasn't one of your options, but you can pop in the 2.75s while looking around for the "just right" set of gears.

 

I don't think 2600 is a bad highway cruise rpm for a 289 v8. For a 300 inline maybe. But not that small v8.