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Discussion Starter #1
From what I've heard lately, 3.73 gears normally are put on cars with Manual Transmissions, and 4.10s are put on cars with auto tanny's. I have an Auto, should I go with the 4.10s or with 3.73s? This will be my first substantial mod so I want to do it right.

Now, I do not plan on ever putting in a blower, so the teeth on the 4.10s wouldn't be too short in the future. I might stroke the engine eventually (next year) but I'm not sure if that would indicate I should get 3.73s or not.

Thanks!
 

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With 3.73s:

5500rpm in first gear = 37mph
5500rpm in 3rd gear = 90mph

With 4.10s:

5500rpm in first gear = 30ish mph
5500rpm in 3rd gear = 78ish mph


You don't want to shift into 4th gear when you run the car on the quarter mile, do you? I went with the 3.73s for that reason only.
 

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gears...

I agree if I were you I would go 3.73... @ about 90mph on the highway im pulling about 3000rpm's... SO its prolly a wise decision to go with the 3.73 gears ...

8astangs .02 cents
 

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Discussion Starter #5
Does it say in the 5.0 forum that it this thread had been moved? I was wondering why it wasn't getting any responses. :) good thing i checked drive train...

Thanks for the replies though, I'm trying to plan for the future of the Bird right now. 3.73's sound like the wise choice and they're used more often.

Anyone notice any problems or noises after the installation?

When I get back from New York in two weeks, I'm running the bird over to Orlando for the change. :D
 

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JJanney

Hey buddy i Have had no probs or odd noises once so ever with my gears...

I had US-1 muffler do it and the guy there does some amazing work...

I diddnt relize you lived in symrna, i live in Port Orange 10 mins away...

Are you talking about the bithlo trakc in Orlando(Orlando speed World)

I have a friend with a 97 bird, and the other one has a blown cougar...

when ya go down to the track drop me a line and we'll see ya down there..

8astang out....
 

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Drivex, are you sure

about the numbers you posted?? I got 4.10's in mine and I go out the end in 3rd gear at close to or over 100MPH and I have yet to see much over 5000 RPM. I'm not trying to be a smart ass or something but I don't think you are correct. In OD @ 70 MPH my car turns about 2700 - 2750 RPM's. You might want to check that out OK!! Also, with the 3.73 in OD the car will turn a tad over 2500 RPM. I know, I had them in also. Thanks and good luck.
 

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Discussion Starter #8
1MTNCAT, how do you like the 4.10s? You said you had 3.73's also, how do the 4.10's compare?

Thanks for your reply!
 

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Since you are running an AOD, your 1st gear ratio is 2.40
If you tie this to a 3.73 rear, you get 2.40 x 3.73= 8.95 in 1st
                        4.10 rear, you get 2.40 x 4.10= 9.84 in 1st
                        4.30 rear, you get 2.40 x 4.30= 10.32 in 1st

Now, if you wish to have your cake, and eat it also, get your trans gone through and have Ford Racing low gear set put in it. These will give you a slightly lower 1st gear ratio to help launch the heavier cars, and have very little differance at highway speeds from stock.

Sample 3.55 rear, you get 2.84 x 3.55= 10.07
          3.73 rear, you get 2.84 x 3.73= 10.59

so, you can launch better than a 4.10, and cruise as a 3.55 or go with a 3.73 and 2.84 1st, and leap off the line with a 10.59

The ratios are 2.84 1st, 1.55 2nd, 1.1 3rd, and .67 OD (Same exact gears that come in the 4R70W)
Std ratios are 2.40 1st, 1.40 2nd, 1.1 3rd, and .70 OD

The cheapest place I foud for them: $436
http://www.usaplaza.com/scripts/wcom_producttree.asp?StoreID=1078&ProductID=32362
 

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Discussion Starter #10
Wow, that's good to know. I'm looking at those wide ration gears now, and will book mark them for when I rebuild the tranny. You guys are a wealth of information.

392Bird, I eventually want a stroker also. Can you PM some pics of your setup?
 

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I am just started on it. I had hoped to have it done by September, but I am not getting much cooperation from my wife. She does not want to take on a 2nd job to speed up things, while I am busy working on the Bird :) Might have to see what kind of trade in I can get for her on the remaining needed parts... I am doing a total drive train replacement, so its going to take most of this Winter to complete.
This is the <a href="http://www.oemfordparts.com/PartDetail.asp?S=1&PartID=192&SubCategoryID=10"> engine </a>going in mine.
 

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JJANNEY, GO WITH

the low gear set when you rebuild if you can and and either the 3.7. or the 4.10s will work fine. If you do a lot of long distance driving go with the 3.73. They are a bit quieter. If you want to drag is a lot and aren't going to run it 100 miles per day the 4.10 will be ok. Torque multiplication would really depend on how you choose to use your car. That's the best advice I can give.
 

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392 BIRD, YOU ARE PRETTY GOOD

at the math now all you need to do is get the information right. 94-UP T-Birds and Cougars ALL have the 4r70W Trans in them and that's what my 96 Cougar has got in it. The 4.10's are fine. I also liked the 3.73,s. If I ever planned on changing again I would go back to 3.73's just because they are somewhat quieter. Otherwise, I will stay with what I have. I am trapping 103-104 in the 1/4 and @ around 5000 RPM, in drive. A Fact!! Good luck in your new motor build-up. Hope it does well for you!!!
 

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1MTNCAT:
I posted the information in referance to JJaney, the original poster, who has a 91 Tbird 5.0 It has an AOD. I also posted that the 4R70W trans already comes with the low gear set.
 

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That's cool

maybe I mis understood then. Just wanted to clarify. Be safe. Good luck on your project.
 

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Discussion Starter #16
Yes, good luck, I hope your wife decides to lend a helping hand. :) Your car will definitely fly after that swap.

To all, thanks for the information. A tranny rebuild is still down the road a ways being as I'm a poor college kid, but believe me, it will be done one day. I'm leaning towards the 3.73's now just to be on the safe side. Once again, thanks!
 

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How about a calculator?

Since it seems you guys can't decide what rpm you get with 3.73s or 4.10s....

GO HERE
 

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3.73info

I checked my gagues again and at 90mph its right at 2500-2600rpm's. This is with the 3.73 gears. If i had the chance to do it all over i would go with the 4.10's! I dont know about any one elses car but off the line when my friend and i race he kills me outta the hole. He has a 90 blown cat. with 14 lbs of boost and some other mods. I need to get rid of that limited slip crap!!! These cars are hard to launch given the weight they carry...

8astang .02 cents
 
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