'21 manual 3.73 to 4.09 worth it?

DrZed

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Is there a noticeable performance gain going from 3.73 to 4.09?

Going higher does not seem to be an option for me.. as I have the Procal4 which can only program to 4.09, and while I can monkey with the revs/mile to get the speedometer right, with a higher gear ratio I don't think the rev-match will work well beyond 4.09??

Any experience and advice... thanks in advance.

 

StangTime

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... getting quote now...

Thank you kind Sir.
Very interested in knowing what sort of prices you get back. 4.09's would kick ass with my FP calibration tune. It just looks like a job I would pay a pro to do.
 

Superspirit

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Very interested in knowing what sort of prices you get back. 4.09's would kick ass with my FP calibration tune. It just looks like a job I would pay a pro to do.
Thats exactly the setup I have. fp tune for 18up gt 4.09's steeda x-pipe and dynomax resonators. car rips!
 


shogun32

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If you have a D4 transmission going with 4.09 means your transmission closely matches the experience of the 15-17 owners and their D5 transmission.



3.66 or 4.24​
2.43 or 2.54​
1.66​
1.24​
1​
0.7​
4.003505​
2.594864​
1.757094​
1.23565​
1.005819​
0.768574​
 
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01Romanss

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I’ve got 4.09 gears with h pipe, light steeda rotors, lighter RTR rims and Lund E85 tune. Gears and e85 make it super fun and quick. I had to get Lund to get my tunes changed with 4.09 so my car wouldn’t set off every alarm and go into limp mode. You may not have that problem. I had the safe and secure system which may have had something to do with it. Not sure.
 

Superspirit

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You either have to have a tune or procal 4 in the 19 up to adjust for the 4.09's
 

Jm28192

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Very interested in knowing what sort of prices you get back. 4.09's would kick ass with my FP calibration tune. It just looks like a job I would pay a pro to do.
I'm getting mine swapped out soon, just waiting on the actual gears to show up. I was quoted 450 for the install. I'm sure this will vary greatly though from shop to shop.
 

shogun32

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Very interested in knowing what sort of prices you get back. 4.09's would kick ass with my FP calibration tune. It just looks like a job I would pay a pro to do.
I'm in talks with Steeda to have them build me a pumpkin. Their in-house tech rebuilds pumpkins for their race cars so they've got a good amount of experience doing it. I wouldn't trust a general purpose mechanic who rarely if ever does these to do it and not make mistakes in shimming and so forth.

I'm starting with the FP 3.55 loaded pumpkin ($1000), putting 3.73 gears in ($200), and replacing the Trac-Lok with a Eaton Detroit dtl-917a731 ($700). So far it's a $2000 build plus labor. So a rather expensive exercise just to convert my MT82D4 with 3.31 into a MT82D5'ish. But that's why I didn't throw money away by giving it to Ford for the High Performance Pack and can instead use funds in more useful pursuits.

Another member here is working on a project to replace the Trac-Lok friction parts and make it vastly more robust and durable.
 

MRGTX

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Is there a noticeable performance gain going from 3.73 to 4.09?

Going higher does not seem to be an option for me.. as I have the Procal4 which can only program to 4.09, and while I can monkey with the revs/mile to get the speedometer right, with a higher gear ratio I don't think the rev-match will work well beyond 4.09??

Any experience and advice... thanks in advance.
So let me add a little splash of cold-ish water here.
I have ~4,000 miles on my 4.09s and I'm very happy with them but it was a very expensive job to have done (or it would be a very time consuming job to do yourself).... and there are some things to consider

1) As far as I've heard, you are correct that the Procal won't accommodate anything past 4.09. It seems like a software update could change this but there's no hint that this is coming.

2) As for messing with the revs/mile, don't bother. You may be able to correct the speedometer this way but it will make everything else go haywire and the rev match will not work. So you're right about that one too.

3) As for your main question, 4.09s have been a very worthwhile mod in my 2020 6spd. That said, I was coming from 3.55s and it was a much bigger jump for me. It's not as valuable of an upgrade in your case and you may decide that this money is better spent elsewhere. Also, if you ever plan to go forced induction, the 4.09s will be less useful.

4) Keep in mind, you won't necessarily see objective performance improvements since in many cases, you'll be shifting more. While it will pull harder in each gear, the shifts between cost you time. As a result, Your 1/4 mile will probably be about the same and the 0-60 may even be a tick slower if you now need another shift. As mentioned, it will make the car feel much more lively and strong and shifting is something most of us enjoy. In a world with 9 second stock electric street legal sedans, fun really is the most important thing.
 

StangTime

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I just found out how much this would cost a mechanic to swap gears. All I have to say is the price changed my mind. I'll stick with my 3.73 gearing. Big thank you @DrZed for the info.
 

NeverSatisfied

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4hrs labor so just under $500.
Does anyone know of an off the shelf housing spreader that works on the super 8.8? i'm half inclined to do The setup myself with gear setup prices what they are and not knowing a local diff shop that I trust will follow the right steps?
 

Mustang_Lou

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Not that I'm considering doing this but would traction be an issue moving to the 4.09's?
 

 
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