390 with Toploader
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Cross-Country
Joined: May 2018
Posts: 64
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390 with Toploader
Im currently building a F100. I have a 390 and a 4 speed top loader. Both out of a 68 Galaxie. With that combo, will 4:10 gears in the rear be a good idea? Its not a drag truck, I just want to cruise with it. I'm not sure what for tires I'm going be running, something close to OEM. Please dumb it down, I'm not an expert when it comes to ratios and gears.
Welder User
Joined: Feb 2009
Posts: 5,269
Likes: 50
From: northwest MT
You can play with a ratio calculator........plug in your numbers.....watch the RPM's. 4.10's would be fun at stoplights but really annoying at highway speeds. With OEM size tires I'd go with a 3.50ish ratio
https://www.randysworldwide.com/calculators/rpm/
https://www.randysworldwide.com/calculators/rpm/
Logistics Pro
Joined: Aug 2007
Posts: 3,773
Likes: 169
From: Pt.St.Lucie , Fla.
Have 3;50's in "Art" the hot rod truck . It has a 428 , C-6 w/ a 3000 rpm stall converter and a '70 nine inch w/ those gears . Am very happy w/ this ratio . You are going to have a ton of fun w/ the BB FORD FE power plant . You will be surprised aw/ the power . "Art " is a blast to drive .
Senior User
Joined: Jul 2003
Posts: 322
Likes: 1
From: FL
The Toploader is arguable the best factory 4-speed out there, but like all 4-speeds, the final drive is 1:1 - 1RPM in = 1RPM out. So, with a 4.10 rear end ratio and a fairly 'standard' 275/75R15 tire, with a nominal diameter of 31.25", at 70MPH, that big 390 is going to be spinning about 3300 RPM. That's a little on the uncomfortable side on the highway - those big FE engines don't like to turn those RPMs (I used to have a 428SCJ with 4:30 rear gears behind a toploader - 55mph was not comfortable on a long trip).
What you have going for you, however, is the low end torque of the 390. You can comfortably run a much higher (lower numerically) gear like a 3.25 or a 3.50. With a 3.25 rear gear, you'd only be turning about 2600 RPMs at 70MPH - much better. And even the 3.50 will only have you turning a little over 2800 RPMs at 70MPH.
What you have going for you, however, is the low end torque of the 390. You can comfortably run a much higher (lower numerically) gear like a 3.25 or a 3.50. With a 3.25 rear gear, you'd only be turning about 2600 RPMs at 70MPH - much better. And even the 3.50 will only have you turning a little over 2800 RPMs at 70MPH.
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