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All AOD equipped SC's had 3.27 gears and 225/60/16 tires. 4th gear in an AOD is 0.67:1, so 55mph in OD with 3.27s would be just over 1500rpm. 3.08s would be about 1450rpm, and 2.73s would be about 1300rpm.
 

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The biggest problem is that there's not enough torque to run 2.73s and the 1st gear in the AOD.

Well, there is, but you'll lose out on the first part of the 1/4 mile due to having to get up into the torque curve.

Why are you looking for longer legged gearing? *is curious*

RwP
 

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Discussion Starter #4
I have 2.73s on my car and it really kills the acceleration. I'm thinking about going with the 3.27 to increase 0 to 60, but I also want the good mpg. Also, i dont have a super coupe, I have the 5.0. The reason I'm asking is because it's the "best" thing to compare it to 😕
 

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Actually, no, the SC isn't the "best" thing to compare it with; the best thing is a 5.0HO.

The 3.08 was the stock issue most years; and it does tolerable at best. A 2.73? I bet that car feels like a dead pig off the line.

I've got some 3.55s to go into Ruby as I redo her drivetrain; 3.73 is about as stiff as I'd go for a highway-also car, but YMMV natch.

RwP
 

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I think this is a trick question because who would actually drive 55?

They put 2.73's in V8 T-Birds for years, pretty much all years in the 70's and 80's. In the 60's they used 2.75's with the 429's. Talk about a waste of big block power.

I am curious which year the OP has, and if he actually has 2.73's. If it's an 88 or older, definitely!

Al
 

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Discussion Starter #7
Not a trick question. I own a 91 5.0 and I'm using it for daily driving. The roads I'm getting on are 55 mph. The 5.0s in 1991 were equipped with either a 2.73 or a 3.08
 

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That’s not true. Unless you or someone before you changed the rear gears, you have either 3.08s or 3.27s. The only MN12s that came factory with 2.73s were the 5-speed SCs. The fox body cars could be had with the AOD and 2.73s, but they also had shorter tires, and were at least 400lbs lighter.
 

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That’s not true. Unless you or someone before you changed the rear gears, you have either 3.08s or 3.27s. The only MN12s that came factory with 2.73s were the 5-speed SCs. The fox body cars could be had with the AOD and 2.73s, but they also had shorter tires, and were at least 400lbs lighter.
This is incorrect -I have a 91 Cougar LS, 5.0HO, stock 2.73 rears switched to 3.73's about a 1 second improvement in 1/4 mile times, LOL. 5000RPM shift out of first was at 60 mph or so:grin2:
 

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And yes, horribly slow until about 3800 RPM. Down shifting at 35MPH was fun though, before I knew how slow it still was...
 

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What does the door tag list under axle?
 

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I'm about an hour away from the car unfortunately. I'll look at the tag when I get a chance. Was under 1400 rpm at 55, just over 1600 at 70. I worked at a Ford dealership during college when I did the gear swap. Discussing options with the Ford tech we decided to find a junkyard rear with the trac-lok to build while I was still driving the car with the 2.73 open diff. I've been mistaken before but don't think I am here....
 

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It could be that the junkyard diff you got had 2.73s, since all the early SCs got a trak-lok, and nobody wanted the 2.73s so they were always cheaper than the 3.27 ones out of the autos. The door tag will tell for sure what was originally in there though.
 
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