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So actual rearend is probably a 60 based on several clues. What gears are people running in trucks that will go 55-60 mph? I probably won't be carrying heavy loads. I live out in the country so 45 mph is a little slow to go anywhere. Would a 3.55 be a reasonable compromise? Thanks
I have the 3 speed. I believe 1-1 final gear, no overdrive. I have 2 sets of wheels and tires. I have a good set 32" tall and an experimental old set 37" tall. I was trying the 37's to see if that would raise my top speed enough. Currently I have only tried them in the back. Not sure if they would work in the front yet. Very worn out, I would need to replace them if I decide to continue down that path.
Just based off how my worn out Flat V8 is with the T98 4 speed (granny low 1st) and 3.73's I'd think 3.55's "might" be a little too tall for 32" tires and no good for 37's. My tires are spec'd at 32.73" tall and at times I have to take off in 1st. I can get over 65 MPH on the top end. Cruises nicely without lugging. I don't have a tach and I used GPS on my phone for speed.
The 3.55's seem to be a good choice for the F1 guys with smaller tires based on a bunch of forum posts. The gear ratio calculators are worth looking at. Gear swaps are too expensive to re-do if you're not happy.
I have been playing with the numbers. I talked with an old school mechanic today. He is going to look into options for me. I only want to do this once, that is why I am asking questions. I have added a tach, and I also use an app on my phone for speedometer. I will follow up when I actually do this project. Thanks for all of the input.
These f3's originally had a 7.50-17 tire which I think is a 33-34" tall tire. Small tires look kind of odd in our larger wheel wells. Once you decide on your tire/wheel package you'll have a better idea of what ratio to run.
My 32" tall set is pretty good. I will probably use them. The 37" are an experiment to see if that would make enough difference. They really didn't help much. My truck currently runs great at 45mph. 50 is doable, but seems like I should ony do it for a short distance. It can hit 55, maybe downhill with a tailwind?
Using a calculator I have, with the 32" tires and existing 4.10 gears you are only turning 2600 RPM at 60. That is perfectly acceptable for a flathead. These are not large engines, and you are pushing a truck with the aerodynamics of a barn door through the air. Gearing lower may not put the engine in a range where it can make enough power.
I have never gotten it to 60mph. I might have to check my tach. That is what calculations show, but my tach is showing that around 50mph? I use a phone app for my speedometer.
Then maybe you don't have 4.10 gears. 4.86 gears would give you close to that RPM's at 50. Only way to be sure is to pop the cover and start counting.
That might explain it? I did mark the tire and driveshaft and spin it. I got just over 2 turns of the driveshaft for 1 tire turn x2. That roughly says 4.10 tag is correct?
Using a calculator I have, with the 32" tires and existing 4.10 gears you are only turning 2600 RPM at 60. That is perfectly acceptable for a flathead. These are not large engines, and you are pushing a truck with the aerodynamics of a barn door through the air. Gearing lower may not put the engine in a range where it can make enough power.
Rotflmao, ''a truck with the aerodynamics of a barn door'', Oh my god. This made my night, lol. So true, yet we still love em just the same. lol
Then maybe you don't have 4.10 gears. 4.86 gears would give you close to that RPM's at 50. Only way to be sure is to pop the cover and start counting.
I ran it up the road today with the 37" tires. I was shuffling vehicles so I could get to my lift. 45mph @2000rpm. I think that calculates really close to your figures. Looks like I need to pull the cover. Label says 4.10.
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