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Discussion Starter #1
As my Cougar restoration progresses power-train decisions must be made. I"m probably going to stow away the original engine in my garage and purchase an engine from Ford Racing. This brings me to the transmission: should I rebuild the original C4 or buy a 3 speed AOD transmission and have it rebuilt? I plan on making a lot of miles with this car, long trips and no racing. It has a 8" diff with 2:79 gears, although I suspect they have been changed up. Regardless, if they have been changed I'll be putting them back to 2:79 ratio.

Any thoughts, suggestions and/or opinions are always appreciated.
 

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An AOD trans is typically at least a 4 spd or more - it significantly reduces your final drive ratio - http://en.wikipedia.org/wiki/Ford_AOD_transmission

A 2.73 rear is already a good "street" gear for economy.....so adding more reduction will not harm anything except your performance if that's a concern.........it's a balancing act performance vs grandma
 

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You won't like 2.73 with AOD, go with at least 3.25 or 3.50.
 

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Assuming you are running the typical 26" tall tire our cars require, that is ~770 tire revolutions per mile. Multiply that by your rear gear ratio and that's your engine RPM at 60mph for a 'normal transmission with a 1:1 high gear. For an overdrive trans, multiply that number by the trans overdrive ratio for the engine RPM in OD.

For example, your 770tire rpm by your stock 2.89 for 2225 engine RPM at 60mph in Drive. The AOD has a .67 OD ratio, so that is ~1491engine RPM in OD.

If you went up to a 3.25 rear axle ratio, the numbers would be ~2500engine RPM at 60mph in Drive and 1677 in OD.

Now you have to ask yourself - what is your new Ford crate engine's powerband? Which rear gear ratio suits that engine better? An engine that is lugged down, or operating below it's best power/torque will be a slug and waste gas.

As an example of lugged down - my wife used to have a '77 Marquis with a 460 and 2.42 rear gears. Good for ~11mpg. I did a 'mild' cam change, with a 'straight-up' timing set (Ford originally retarded the cam using a relocated keyway on the crank gear), added 2-1/2" duals, and a 3.25 posi rear. The car had a lot more ooomph off the line (read: more fun to drive ;) ), and still got 11-12mpg! Yeah, it probably no longer met emissions standards, but it was just as efficient with fuel use!
 

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Discussion Starter #5
Thank you gentlemen. All things considered, I think I'm just going to rebuild the original C4 and leave it at that.
 

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Sounds like your lowest $ route for sure....and at some point you can bump up the ratio if you feel the need and still be well under the conversion cost....a small block C6 would net you a stronger trans though, for not much more if your rebuiling anyways......just a thought. C4's can be beeefed up as well....
 
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