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Discussion Starter #1
Since I'm going with the AOD, I am probably going to change out the rear end. The car is a 68 with a mild 302 and currently has a 3.00 ratio. I figure with this OD would only be good on the highway. I am leaning towards a 3.55 to 3.73, probably the 3.55. Fuel economy is important to me since this is my driver, but I do want a little more than the 3 to 1. So do you guys think this is a good selection?
 

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Most guys I know go with at LEAST 3.73's with an AOD. 4.11's are pretty common in an AOD applications too...

Gives you the best of both worlds. Fuel economy and rocket ship style acceleration.

Check out THIS handy gear ratio calculator...
 

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performance OR fuel economy, pick one.
If you are leaning twards the 3.73 just go for the 4.10's. It wont cost you that much more. If I were you I would get 4.56. That will really get the blood flowin. You would be surprised with how little the difference makes with fuel economy.

I had 3.55 in my bronco and went to 4.56 and didnt spend a whole lot more $ on gas. E4OD tranny (4spd)
 

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If you do a lot of freeway work try and get gearing so that you are not doing more than 3000 rpm at 70mph. It will be a lot more pleasant. Over that you start to chew through gas
 

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I am running 3:73 gears with an AOD. My motor would like more gear because it lugs in od due to the cam I'm running. At 55-60 I'm running aproximately 1700-1750 rpm. At 80 I'm running 2200 rpm just to give you an idea of where your rpm's would be. The next thing to consider is the speedo. With the 3:73 gears and 275/60/15's (tall) my speedo is correct with a 21 tooth speedo gear. If you go deeper on the gear then you will need a bigger speedo gear than ford makes so you will need to go to aftermarket which doesn't last long (I've heard) or a custom gear reducer for the cable. If your motor is stock or with a small cam and you don't have small diameter tires I would recommend the 3:73's. If you have a big cam go deeper on the gears. BTW my car only gets around 12-14 mpg but like I said my cam is for power not mpg.... disappointing mileage.
John
wvcat
 

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Discussion Starter #7
I've got a 302 running a very mild cam (edelbrock performer...not performer RPM). I had read some info about the 4.10 and speedo gear problems. This is my daily driver and thats a headache I don't need. If I ever decide to race it (or if I have a problem with the Ricers at stoplight derbys), I think I'll go 4.10 or higher. As it sits, I'm still leaning towards the 3.73 and will probably order it and a posi unit tonight. Thanks for everyone's input...I really appreciate it.
 

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Alex,
I used to live in Escondido. I just moved to Temecula, 30mi north. Guess its time to update my profile.

-Austin
 

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Discussion Starter #9
3.73 for 8 inch

Anyone know of anyone who makes a 3.73 ring and pinion for the 8 inch housing? All I've found was 3.8, which is no big deal...just curious.
 
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