Rear gear swap effect on quarter mile

[smoke_wagon_6g]

I have an 18 manual with the 3.55 LSD.

The instrumented tests of the 2018 Mustangs you find on the web and in the magazines are done with the PP Mustangs that have 3.73 Torsen rears. I want shorter gears like the PP, but even shorter.

I'm actually looking at installing the 4.09s since they ought to be a blast around town. I live in second and third gear most of the time anyway.

Does anybody have back to back 0-60 and quarter mile times available where the only change is rear gear?

I'm curious if my 3.55 is running the same times as a 3.73 PP with the same HP, and if true, if the 4.09s would pick up any time over the 3.73s.

This is again with an MT-82. I know the auto has shifting programming that would be confused. And I'm aware that the speedometer and MPG are affected. The way I see it a tune wouldn't even be required unless the speedometer error is annoying.

This is the ring and pinion I saw available:

https://performanceparts.ford.com/part/M-4209-88409A

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[Schwerin]

For some perspective, I have 3.73 and am looking at the 4.09 also. My MACH1 had 3.55 stock and the gearing in the MT-82 is not to far off from the 3560 in the MACH1, its nearly a 3650 with longer first and a 6th gear slapped into it.
1st, +.14
2nd, +0.1
3rd, +0.1
4th, +0.0 - identical
MT-82 5th is .81
MT-82 6th is .62, same as MACH1 5th.

Moving to the 4.10 was noticeable in the MACH1, only mildly in MPG, but definitely when punching it. It was more eager to blow the(stock tire) wheels off(even downshifted on the highway once and spun them some). I would imagine that 3.55 to .73 is good for a couple 10th's and that going to 4.09 would be a few 10th more. I remember from the MACH1 forums one guy went from 13.2 to 12.8x with JUST a gear change. Around town it was fine, even in city driving. I was rarely out of 3rd or 4th unless I was on the highway.

I would get a tune as the speedometer and odometer may also be incorrect.

 

[ugstang17]

Along with a shorter gear comes the need for better traction. A group of us met up years ago with our 2011-2014 GT's. All were stock. I ran a 3.31, one guy ran a 3.55 and the other three all had 3.73's PP. Everyone was stock and on street tires. My. 3.31 and the guy with the 3.55 were the only two to find a 12 sec pass. The 3.73 PP cars were unable to get enough traction to take advantage of the shorter gear. None of us were veteran 1/4 mile guys at all. Everyone was just a weekend T/T warrior at best.

While this was an S197 w MT-82 compare it exhibits the importance of traction correction with a shorter gear. Getting traction will be your goal after dropping to a shorter gear. But given the proper tire and suspension setup the shorter gear will yield a quicker time at a lower MPH trap speed v your best ET/MPH on your stock setup.

BTW your speedometer will be off by 5% going from a 3.55 to a 4.09 gear. But it will be off in a good way. You'll be going slower than the displayed MPH. So at 60MPH you will be running closer to 57MPH (plus whatever the speedometer is off to begin with)

 

[mohadnuj111]

I am also considering changing to 4.09, the 3.55 gears are too long for me.

here's 18 gt with 4.09 and bolt ons



found another one

 

[smoke_wagon_6g]

I am also considering changing to 4.09, the 3.55 gears are too long for me.

here's 18 gt with 4.09 and bolt ons

I appreciate the post but those videos simply aren't very clear. What's the HP? Are these forced induction? There's other threads of discussion for speculation. I'd like actual numbers if possible. Sometimes a car mag in the old days would print acceleration numbers before and after a rear gear swap but I can't find one that is similar to our Mustangs. The MT-82 ratios, plus our combination of high redline and HP/Tq are not the old days stuff.

A video of a car actually running the full quarter might do it but then you have bolt-ons and so forth so it's hard to compare unless you have a single car modded the same with two different gearsets and two passes to compare apples to apples.[/QUOTE]

 

[Ghost50]

I’m interested in this too. When I bought my car (2019 MT82 PP1) the first thing I noticed was the lack of bottom end torque. I even started a post on how it felt sluggish until it hit the 3500-4000+ RPM bands.

I came from the Fox Body/SN-95 platform and ran 4:10’s on several of my cars and loved them.

However the concerns on these cars about them not hooking and the MT82 gear ratios are valid.

My 3:73’s spin the tires (the ps4s) like crazy. So upping to 4:09’s would definitely need to be accompanied with the suspension upgrades and better tires. I’d have to step back down when I go FI but once I see a few more people going with the 4:09’s is when I’ll be able to weigh whether I want to do it or not.

 

[Mikepol2]

I have a 2018 GT PP1 6-speed and am actually thinking about 4.56's, which are now available from Yukon - but I don't plan to run any 1/4 miles, it's just for fun in the hilly twisty Western PA roads. At max torque, the force applied to the road by the rear tires in my current car is about 2200 lbs. For the base GT with the 3.55's it's around 2100 lbs, 4.09's would be around 2400 lbs, and 4.56's would be around 2700 lbs. There's a guy in the GT350 threads who installed 4.56's and loves them, but he's got some extra top RPM to play with too. I really think 4.30's would be the answer for us GT guys but nobody's making them yet for the Super 8.8's. I emailed U.S. Gear asking about it but they've got no plans for 4.30's for now.

 

[Mikepol2]

Found a local speed shop that will replace my 3.73's with 4.09's for $225 if I bring them the pumpkin and the new gears. Has anyone removed and replaced their pumpkin themselves? Looking for any pointers or potential things that could get me into trouble...have done enough work on cars to know that the first time you do anything, you're gonna run into something that you would do differently the next time!

 

[PoppinJ]

Found a local speed shop that will replace my 3.73's with 4.09's for $225 if I bring them the pumpkin and the new gears. Has anyone removed and replaced their pumpkin themselves? Looking for any pointers or potential things that could get me into trouble...have done enough work on cars to know that the first time you do anything, you're gonna run into something that you would do differently the next time!

There are some posts in the HPDE section where guys have installed the diff cooler that detail their experience taking the diff out. Might check that out.

 

[ckendri]

Found a local speed shop that will replace my 3.73's with 4.09's for $225 if I bring them the pumpkin and the new gears. Has anyone removed and replaced their pumpkin themselves? Looking for any pointers or potential things that could get me into trouble...have done enough work on cars to know that the first time you do anything, you're gonna run into something that you would do differently the next time!

It’s pretty gravy work, and straight forward. There aren’t really any tricks that I recall. You just remove a few bolts from each side, pop out the axels, remove four more bolts, and out it comes. A couple of hours worth of work to get it out, and anyone should be able to do it.

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