Top speed with 4.09 rear gear and MT82?

[Dave2013M3]

After 2019 you need a tune for 4.09. I was pretty sure the S650 wouldn't allow it without a tune. We are probably 3-4 mos. away from getting a tune for these cars.

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[Zig]

After 2019 you need a tune for 4.09. I was pretty sure the S650 wouldn't allow it without a tune. We are probably 3-4 mos. away from getting a tune for these cars.

You can tune it now for the low low price of 5+k.

edit: make that 9+k

 

[ThreePedalPlow]

Yea, my hope was to do it after Ford releases a tune but only if I'm not happy enough with the improved low end. The Ford tune on the S550 added a lot of low end torque. I'm hoping it's a thing where I can reflash it or reprogram it after adding the 4.09 rear end if that is possible. Not sure how the one on the S550 functioned exactly.

 

[Darkness24]

You can tune it now for the low low price of 5+k.

edit: make that 9+k

Remember though that (just say 10K) gets you up to 800HP or so at the crank. So to me if that's what you want it seems relatively inexpensive for that much horsepower. Considering what you may have paid for a new 2024 Mustang Gt or Dark Horse!

 

[24 vert]

About what do you think top speed would be with a 4.09 rear gear with the MT82 transmission? I know Ford limits the car to 155 mph from the factory and I'm wondering if a car with that type of setup would still be able to reach those speeds.

I think the best way to break it down is with the data/calculations. By my calculations, you should be fine. You won't hit the rev limiter in 5th (182.91 mph @REDLINE in 5th) because the speed limiter @ 155mph will kick in before that.

I used the calculator on the Tremec website (https://www.tremec.com/calculadora.php) and used my 2024 MT82D4 Performance Pack as a starting point and plugged in different commercially available gear ratios to see how the results would look. Used the performance pack rear tire size 275/40-19, redline assumed as 7400 rpm.

rear end ratio: top speed MPH @7400 RPM in each gear(1st,2nd,3rd,4th,5th,6th)

3.73: 50.44, 77.6, 114.8, 163.26, 200.57, 262.48
4.09: 46, 70.77, 104.71, 148.89, 182.91, 239.38
4.11: 45.77, 70.42, 104.2, 148.17, 182.02, 238.21
4.56: 41.26, 63.47, 93.91, 133.55, 164.06, 214.7
4.88: 38.55, 59.31, 87.76, 124.79, 153.3, 200.62

All require 1-2 shift for 0-60 anyway. 4.88 requires 2-3 also. All my fun on the street keeps me out of triple digits so the shorter the gears, the more I get to enjoy banging through them. The 3.73s I would not even be winding out third on the street because it's too fast for comfort.
Personally, I'd do the 4.56 and accept the highway fuel mileage penalty as a trade-off for the excellent in-gear acceleration. IF you have windy roads, might be too much gear changing when hustling/frequent stop and go. The other benefit with 4:09 and up is for dyno testing in that 4th gear 1:1 will no longer conflict with the 155 mph speed limiter. The other potential drawback for these steep gears is you will definitely have to take them out if you decide on forced induction as you'd just be making tire smoke instead of forward motion.

I'm just waiting for someone to pull the trigger and try 4.09 or higher gears and sort out the speedo error/rev-match issues...maybe there is a way through for-scan or similar?

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