4.09 Gears in 2019+ M6 questions

[2016S550]

I'm running the 4.09s with the Ford Performance/ProCal4/CAI/throttle body pack.
IMO, 4.09s are a completely positive change to 18+ GT manuals and WELL worth it for folks coming from the base 3.55 ratio like I was. The new ratio allows you to keep the engine in the sweetest part of the rev band in more situations without going to jail and the change just makes the car feel happier somehow.

The swap is labor intensive. If you already have 3.73s, the change isn't going to be quite as significant. That may seem obvious but it's worth keeping that in mind as you size up the job or get quotes on having it done.



Unless something has changed since last year, I don't believe this is correct. I tried and tried and had no luck with Forscan. There's something in the logic of the rev match software that just isn't fooled by altering the tire diameter.

If I remember correctly you had a Lund tune that was working after some difficulties. Why did you transition to the FMS? Thanks

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[MRGTX]

If I remember correctly you had a Lund tune that was working after some difficulties. Why did you transition to the FMS? Thanks

In a nutshell, the car just didn't behave quite right with the Lund tune, they said they couldn't help me make it any better than what they already sent so I bailed out. I could elaborate but that's about it.

Honestly, I wouldn't have gone with Lund at all but Ford's tune for the 2020 wasn't ready yet.

Unfortunately, I didn't know this going in. My Ford service department erroneously said there wouldn't be any problems adjusting the PCM for the new ratio and they included that service in the quote...and ultimately handed the car back to me in non-working order so I had no choice but to roll the dice on one tuner or another.

It was an ordeal.

 

[2016S550]

Yea…I remember that thread. Glad its all good now and I appreciate the feedback.

 

[Seanuf99]

I am waiting on delivery of the FP calibration kit, and was seriously considering the 4.09 ratio as the next project. Thought was to run the stock 2021 18 inch wheels and AS tires in the winter, but adding perf pack or similar style staggerds with summer tires the rest if the year. This is a DD, but I work from home so most driving is just for fun. I try to not drive in ice or snow but it does happen on rare occasion. Anyone experience or have any words of caution with this set up?

 

[MRGTX]

...

You'll need 91 octane going forward. The ratio doesn't matter in the computer with the 6MT only with the AT. You can also adjust tire size separate from gear ratio (again, not necessary for 6MT) any time in the future with the ProCal 4 that comes with the tune if you ever do change tire diameter.
...

I see you have a 2018 but this info is flat 100% wrong for the 2019+ manual cars with rev match. For those cars, a tune IS REQUIRED.

This seems like an important clarification for anyone who might be searching this thread in the future.

 

[01Romanss]

I’ve got a 19GT PP1 6MT. It has the safe and secure system. I put 4.09 gears with a Lund tune. Once I drove the car with the gears it set off every alert on the car. Blind spot, collision, etc and went into limp mode. Couldn’t flip the toggle switch to sport or any other setting. Lund sent me another set of tunes for flex, 93 and e85 for 4.09. It worked. The car is amazing to drive. With 4.09s and e85 it is twice the car it was. Do it!!!

 

[WildHorse]

FYI, you cannot make the needed changes with forscan! It has been addressed on here and attempted many times.

Rear Axle Ratio (4.10) Enabled BCM 0726-12-01 019A xxxx xxxx
^^ close enough to a 4.09

 

[Superspirit]

Rear Axle Ratio (4.10) Enabled BCM 0726-12-01 019A xxxx xxxx
^^ close enough to a 4.09

It's been tried, won't fix it.

 

[NeverSatisfied]

It's been tried, won't fix it.

Sucks there’s no stock tune fix. Want 4.09 but need to retain 87 octane fuel use option. don’t want to go aftermarket tune while under warranty.

 

[Marketplaza]

I’ve got a 19GT PP1 6MT. It has the safe and secure system. I put 4.09 gears with a Lund tune. Once I drove the car with the gears it set off every alert on the car. Blind spot, collision, etc and went into limp mode. Couldn’t flip the toggle switch to sport or any other setting. Lund sent me another set of tunes for flex, 93 and e85 for 4.09. It worked. The car is amazing to drive. With 4.09s and e85 it is twice the car it was. Do it!!!

Hey, it’s funny as you have the same exact set up that I had. I recently installed a vortech and had to go back to 93 until I get a fuel system. But I had your exact setup and mine is a 19 mt6 as well. You would love a vortech or Paxton. They work really well with that set up. Don’t go PD as you’ll have to change gears. But I’m am really happy with the vortech.

 

[01Romanss]

Good to hear. Did you upgrade your clutch as well? Who did you use for the vortech 93 tune?

 

[WildHorse]

It's been tried, won't fix it.

Then obviously that 4.100 code is exclusive to the F-series trucks.
FORD has all kinds of access, all other tuners hack they're way around it.

 

[Jaymar]

Then obviously that 4.100 code is exclusive to the F-series trucks.
FORD has all kinds of access, all other tuners hack they're way around it.

That's not as obvious as you may think. One section of the code can pertain to one thing (i.e. speedometer) while that same aspect may be referenced someplace else entirely by separate code (i.e. PCM for rev blip) even though it is the same outside variable in this case rear end ratio. The two modules may even check with one another to see if they have the same value but a mismatch can be handled in many different ways. Since these parts are multi-use, it actually makes sense that everything isn't central even though it looks like a clusterfark.

 

[WildHorse]

The two modules may even check with one another to see if they have the same value but a mismatch can be handled in many different ways.

That happened when I changed tire circumference. Got a p0160. Did the forced learn, alls good.

 

[PaddyPrix]

If you think the 4.09's are great, try tossing on a smaller set of tires. 315/30/18 from the stock 255/40/19(?) drop from a 27" to 25.5" tire, and the acceleration goes through the roof. Unfortunately, so does the shifting, but it's a small price to pay. The 15-17 gearing is much better for a road racing car than the 18+ MT-82D4 ratios, but a set of 4.09's will bring it pretty darn close to it.

Base GT crew, if you're going to go to all the trouble of popping the rear open, might as well throw a PP or GT350 Torsen in it, absolute night and day difference on the handling should you take it to the track.

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