Fox Why did FORD use such lower sized gears in rear IMO

MrPerfect2

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I have a stock 91 GT AOD with the factory option 327 rear gear . It is nice to cruise around town at 1200 rpms , but off the line it is a slug - I can only imagine what a 308 would feel like ... 25 years ago I had same year mustang and remember putting in 373 and it seemed a lot better - but still no rocket of the line . I heard the Ford motor gears seemed the least problematic of the brands , but the ratio I was thinking ( 390 ) not made by them . Do any of you guys with AODs run 410s and can offer some insight if it’s too much gear ? Would 373 gears be less stress on drivetrain parts and be best for a daily commuter or is it not really worth the hassle to go from 327 to 373 ?
 
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91TwighlightGT

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Most people change the factory gears in search of more performance.

3.08 was the "performance" gear for the T-5 (manual transmission) equipped cars. If you didn't get that, then you got the 2.73 gears!

Things were different back then, and one of the ways the manufacturers tried to increase fuel economy was with taller rear end gear ratios. 3.55 is the common upgrade choice for a manual transmission, but 3.73 is also popular. For automatics, 3.73 is popular and 4.10 is viable. You will see more RPM on the highway and a slight decrease in fuel economy. Drivetrain wear is not a concern, but technically running more RPM will mean more wear over time.
 

Mustang5L5

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I went with 3.73s when I was AOD. I felt like it was good enough if you do a lot of highway driving. However since you can’t go WOT in Overdrive it limits you to a max of 100 mph give or take at WOT. An issue when drag racing as I hated crossing the traps at redline.

Now with a 5-spd, I’m not a fan of the 3.73s. I love highway cruising and will be swapping for a 3.27 gearset after I feel out my motor build
 

revhead347

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All the V8 sports cars came with anemic rear end gears. Mostly for fuel economy, or that's just how they did it. Who knows?

Kurt
 

Mustang5L5

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Will I feel a lot of difference going from 327 to 373 - it’s a $700 job with parts and labor

It was a huge diff when I went 2.73 to 3.73.

Now 3.27 to 3.73? You’ll feel it but is it worth $700? I can’t answer that.

Or maybe I can since I’m going 3.73 to 3.27...but I’m doing the work myself
 

Gs87GT

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If your not doing a ton of highway driving I'd go 4.10s with an aod.

I had 3.73s in my foxes back in the day....5 speed cars.

With this 87GT I think I'm going 3.55s. A big improvenent without 1st gear being so low. It has 2.73s now and 5th gear is pretty much useless for the type of driving I do.

Gears always were the biggest bang for the buck. I'd suspect that's still the case.
 

General karthief

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The 4:10 gear will have a noticeable effect with an aod and stock converter. You will run higher rpms on the highway. A happy medium is the 3:73 gear. It depends on where you drive the most.
 

Rt jam

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We all know the solution but the root of the problem was the AOD's 1st gear ratio. 2.4 is pretty tall for a performance 1st gear.

Rear gear ratio alone means NOTHING. It must be combined with the 1st gear ratio and rear tire size as just a starting point of the making a ratio decision.
Multiply the 1st gear ratio with your desired rear ratio. In a typical fox around 9:1 is a good street strip drag gear.

Coyote stock and a 427 Windsor will not be happy with the same ratios.
 

TOOLOW91

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All of you guys talking trap speed and starting line ratio to the op who never plans on racing his car . Looking for a little more pep in his step .

op for a stock car 373 will wake it up a bit and still not have it screaming down the highway .
 
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MrPerfect2

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Thanks all! - seems 373 is good for AOD and the most popular for a daily driver with mainly city use . Got to decide if it is worth the 6-700 $ to go from 327 now ....
 

Neuron

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When I went from 3.27 to 3.73 I think my expectation was to high, the difference to me anyway was kinda disappointing. On the plus side gas mileage and freeway RPM was not affected to badly. I wish Ford made 3.91's like the old days, I think that would be perfect. Not sure about 3.73 but any lower and a trans cooler is highly recommended too.
 

Monkeybutt2000

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I went from 3.27 to 3.73 years back on a 92 LX. Car went from a small chirp in takeoff to boiling the tires after install. Car ran 14.20's in pretty much stock form. I've had buddies run 4.10 and even 4.30 gears in AOD cars. All ran good and dont sweat the rpm,it's not that bad.
 
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