ford 100 speed

[jwpbullfrog]

I have a 1970 f100 with a 351w engine (installed by previous owner). It has 3 speed transmission and 3.25 rear end. It seems to work the engine too hard to travel over 60 mph. My question: what would be the best combination of transmission and rear end to get the best performance out of this engine in this truck?

[flyboy2610]

First off: Welcome to the site! Pop into the Welcome Mat and tell us about yourself and your ride when you get a chance. Nice to have you here!

Third gear in your truck is a 1:1 ratio, and 3.25 gears should be giving good road speed and mileage. If you do have 3.25 gears, you should have a decent highway cruiser there.
About the only thing I can think of is that you might have some clutch slippage going on. How much free play do you have in the clutch pedal?

[72hiboy4x4]

dang, I thought he had found a real 100 speed tranny.
now wouldn't that be fun to drive??

[willowbilly3]

That 351w should be happy with the 3.25s unless you are running 36 inch tires or something.
Maybe you have a timing or carburation issue if the engine is laboring. Or maybe you just aren't used to old trucks and the road noise that they produce.

[oldhalftons]

351w with 3.25's should be fine at highway speeds.
all the automatics, 3spds and 4spds have a 1:1 high gear so unless you get an overdrive transmission, changing transmissions won't help you.

I also think its a engine issue or like willowbilly said, road noise

my 300 with 3.50's doesn't complain until 70-75

[fordman]

i can get 70-75 before i start to feel thats all she has or needs. i've got a 390 c6 with a 3.25

[willowbilly3]

I had a 240 with 4'10s and it would cruise all day long at 70. It was starting to complain a little a 75. Same with my 300 and 3.73s. It will run happily at 80 all day long. My 390 with 3.73s will lope along at a casual 90-95 without even laboring.
Something isn't right. I still think maybe you just aren't used to old trucks .

[fordman]

i've had the 390 that fast but the cops are watching everyone anyway they can now days and i wouldn't want to tell on myself now would I?

[cdeal28078]

My 71 was originally a 302 with 3.25 gears and I always thought the 3.25's to be about the perfect gear unless you do alot of pulling. It'll run highway speeds well without too high of RPM's but still have decent take offs.
I went with 3.70's in mine now that I have an AOD in it but that's because I'm trying to have my cake and eat it to.
Is'nt working though as I'm getting worse mileage now than I did with the c-6 and 3.25's
clint

[steveheer]

It's kind of interesting that you're getting worse mileage. Is your rpm about the same?

I'd think a 3.25 gear if anything would be a little tall in a truck. I have 3.50 gears in my truck. It'll wick up to 85ish and that's about all the rpm the I6 has. But I installed a T85/R11 overdrive 3 speed and in O/D the thing will run at 85 all day! --not that I would do that!!!!

Steve
69 F100 300I6
67 Mustang fb FE 431ci
72 Gran Torino Sport 351W
91 Bronco 351