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What is a good rear gear ratio?


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I am currently rebuilding a 351c, some components are aluminum heads and intake and a comp cam with 230 int/exh at 050. I am also swapping the cruise-o-matic for a 4 spd toploader. I know I need to redo my rear end gears, but I am really unsure on what a good ratio would be? I plan on driving it mainly intown and would like some getup off the line. Any suggestions would be appreciated.

'72 Mach 1

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I agree with Tnfastback, 3.91:1 if you can find them these days. Most makers have gone to 3.89:1, close enough. It depends on what you want the car to do and what you are willing to trade to make it do it. In 78 I was driving an R code Mach to work with a 4.86:1 gear in it. A real hoot but very radical.

 

Good Luck,

Chuck

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Check out roushyatesparts.com, they have several used gearsets in kinda odd ratios but you cannot beat the price. I'm looking at a 3.22:1 set. Their sets are all deburred and polished.

[align=left]Jeff T.

 

When I die I want to die like grandpa, peacefully in my sleep... not screaming, like his passengers. [/align]

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I have 3.50 non posi. Does it or will it make a big difference by adding posi traction instead? when you first take off does posi make a big difference (pick up wise) as far as racing someone in town?

 

Thanks,

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If your vehicle has factory A/C and you have retained it for daily use, any gear over 3.25 will burn out the Tecumseh (factory) A/C compressor. The compressor will just spin too fast. This is why the 1971 Boss 351 and 1972 R Code 351 HO--both which came with 3.91 rear gear ratios--could not come with A.C. However, if you go with the new Sanden AC compressor, it can handle the faster spin. But, of course, if you do not have AC, it is a moot point. My 2 cents.

Tim: Restoring 71-73 Ponies, Restoring People

139A1893.jpg

 

 

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I have 3.50 non posi. Does it or will it make a big difference by adding posi traction instead? when you first take off does posi make a big difference (pick up wise) as far as racing someone in town?

 

Thanks,

 

It only makes a difference TRACTION wise. An open rear only puts power to 1 wheel. Ford calls it Traction Lock (Posi-Traction is a Chebby term) for a limited-slip differential. It puts power to both wheels (with some slip for drivability).

To the OP: Why not just put in a TKO-500 (5-speed) instead of the Toploader?? Cost is about the same. You're not keeping it origional anyway.

The 500 has a 3.27 first gear, so you may not have to change the rear gear. It really juiced up my Mach with a 3.00 rear gear. The first gear combo now is equivelent to having a 3.81 rear with a c6 automatic, except now it has a nice overdrive too.

 

1971 Mach1

351C-4v

C6 is history-->>now TKO-500

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