3.15 to 3.73 swap on auto

I don't know where are all those 435 horses, probably lost in the longest gears i have even seen. The auto trans has longer gear ratios than the manual, so why put a 3.15? :frusty:


I'm considering to go directly with 3.73's. What do you think? Pros and cons?

P.s
Don't say mpg

3.15 is great if you plan on going FI also keeps wheel spin down some when launching compared to 3.73. It does help increase mileage, I agree 3.73 would give a more peppy feeling but much more wheel spin if not careful. Just my opinion of course and yes I own a 2016 gt a6 with 3.15 rear gear.

he auto trans has longer gear ratios than the manual, so why put a 3.15?

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3.15s are purely for the economy, especially on the highway.

And that's why they offer the optional 3.55 rear end, which is just about perfect for this combination.

Although not sure why you seem to think that the auto has longer gears than the manual. 1st and 2nd are shorter, the rest are marginally longer.

1st 4.170 3.657
2nd 2.340 2.430
3rd 1.520 1.686
4th 1.240 1.313
5th 0.870 1.000

EFI said:

3.15s are purely for the economy, especially on the highway.

And that's why they offer the optional 3.55 rear end, which is just about perfect for this combination.

Although not sure why you seem to think that the auto has longer gears than the manual. 1st and 2nd are shorter, the rest are marginally longer.

1st 4.263 3.657
2nd 2.538 2.430
3rd 1.665 1.686
4th 1.239 1.313
5th 1.000 1.000

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Your are comparing manual ecoboost with manual gt. I'm talking about auto trans vs manual gt. If i'd put the 3.73 gear ratio i would have longer gears than a manual with 3.55...

Oh oops, you're right I copied over the wrong ones. I updated the post above for the auto numbers. Even with those, they are still pretty comparable in length to the manual. Also don't forget about the torque converter which multiplies torque (something that the manual with a clutch doesn't do). So an auto is not going to need as steep gears as a manual.

But again, Ford gave the option of 2 rear end ratios for different types of driving. Also many people agree that the 3.73s with the manual are too much gear, and a lower 3.55 is more desirable. So the auto with 3.55s is a great combo.

These are the correct ones:

1st 4.17 - 3.657
2nd 2.34 - 2.43
3rd 1.52 - 1.686
4th 1.14 - 1.315
5th 0.87 - 1.00

The % of difference between each gear is more than the % of difference between 3.55 and 3.73.

About the torque converter i agree with you, it works very well but at low rpm. Actually i get a bit of fun only in 2nd gear. If i pull the 3rd I arrive at 120mph and I don't know if i'll stop on the road or into the jail.

i had a 2011 i went from 315 to 410 and loved it!!!! would kick ass out of the hole and roll racing was killer too.

Auto gearing 1st and 6th gears shorter and 2-5th longer compared to the manual.
You won't gain much more performance with more gear but it may feel more fun to drive. 1st will become useless and 6th will have a higher cruising rpm. If you care about the 1/4, the wrong gear choice may even make you slower. I'd add more power first. Maybe even try a throttle booster like pedal commander or pedalmax; won't add power but will liven things up.

[ame]

Listen to the douchebag.

I'd go to 3.31 or 3.55, not 3.73. Know a guy who went to 3.73 and I wasn't a fan. Just spins tire all day.

The 3.15's are a great gear for the autos. I went 11.2 with that gear with just a few bolt ons. They feel soft out of the hole because of the super tight torque converter. A converter is the way to go after a good tune obviously.

wildcatgoal said:

I'd go to 3.31 or 3.55, not 3.73. Know a guy who went to 3.73 and I wasn't a fan. Just spins tire all day.

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Of course if you just stand on the pedal and think that that's what makes it fast you're going to fail; throttle control.

My situation, with the 20" wheels, auto and 3.15, actually is this:

Gear => mph @ 6800 rpm / GT / auto / 3.15 / 20"

1st -> 40mph
2nd -> 75 mph
3rd -> 112 mph
4th -> 160 mph
5th -> 200 mph

The max speed is reached in 4th and the 1st is totally useless, so, talking about performance, i have 3 gears for fun.

If I swap to 3.73 the situation will be this:

Gear => mph @ 6800 rpm / GT / auto / 3.73 / 20"

1st -> 35 mph
2nd -> 63 mph
3rd -> 98 mph
4th -> 130 mph
5th -> 170 mph

The first would be always useless, the second would be much more fun, but still good for 0-60, and in the third I would feel much more torque. The 5th gear, with a bit of more power, would allow me to reach that speed.


Now, as benchmark, lets see how are the speeds with a GT, manual, 3.55 and 19", that seems considered by everyone the best combo.

Gear => mph @ 6800 rpm / GT / manual / 3.55 / 19"

1st -> 42 mph
2nd -> 62 mph
3rd -> 90 mph
4th -> 116 mph
5th -> 154 mph


Considering all this, if I did correctly the maths, is there any reason to consider a 3.55 good for a manual and a 3.73 too much for an auto?

I am in process of going twins. While stock I installed a circle d converter to go along with my 3.15. My friend has stock car and 3.55. From a dig I put 3-4 cars on him by 100mph. From a 40 roll I get him by 2 cars.

Keep the 3.15!

Reds197 said:

I am in process of going twins. While stock I installed a circle d converter to go along with my 3.15. My friend has stock car and 3.55. From a dig I put 3-4 cars on him by 100mph. From a 40 roll I get him by 2 cars.

Keep the 3.15!

Click to expand...

What this circle d converter does exactly?