4.09 gears.

I'm building a complete diff for the car so I can swap between gear sets as needed. I am also going to swap in a CF drive shaft when I do the swap.

Conedodger said:

I'm building a complete diff for the car so I can swap between gear sets as needed. I am also going to swap in a CF drive shaft when I do the swap.

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I love the idea of having two diffs.

I think all Mustangs as delivered from Ford will benefit with more rear gear. Ford does not put the optimal gear in the Mustangs because of CAFE. A 4.09 gear sounds good, a 4.56 would be interesting.

Hi-PO Stang said:

I think all Mustangs as delivered from Ford will benefit with more rear gear. Ford does not put the optimal gear in the Mustangs because of CAFE. A 4.09 gear sounds good, a 4.56 would be interesting.

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That's what I suspected. I can't imagine how awesome these cars would be with 4.56 final drive, fuel economy be damned.

Any insights on what a quick-change differential might look like would be very welcome. The only analog that I'm familiar with is the ancient Chrysler 8.75" with a very easy to swap center section (out the front of the axle assembly).

With aftermarket axles, these are fairly easy to swap out.

Conedodger said:

I took the plunge and ordered M-4209-88409A and M-4210-B3 for my GT350 R. I will let you all know how it works out in a couple of weeks.

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You may want to call Ford Performance to find out why the 4.09 gears were dropped. I had a conversation with them months ago about this.

I found it on Summit. US gear makes it.

https://www.summitracing.com/parts/ugr-0788841115is/overview/

Or here. I like this one better as they offer the lightning version.

http://www.usgear.com/p/high-performance-product-catalog.pdf

jma406 said:

You may want to call Ford Performance to find out why the 4.09 gears were dropped. I had a conversation with them months ago about this.

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Do tell...:gossip:

So what do you do with the ECU to correct for these gears?

stanglife said:

So what do you do with the ECU to correct for these gears?

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You can use a whipple device or forscan if your talking speedometer correction.

Update: Estimated ship date 3/3

BTW, there is a 3.91 available also.

Update. The gear set arrived today so they do exist. That is the first hurdle crossed.

Nice!

I should go ahead and order then.

Conedodger said:

Update. The gear set arrived today so they do exist. That is the first hurdle crossed.

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Pics or it didn't happen lol