3.73 vs. 3.55 vs. 3.31
 

Hey guys I am trying to decide between 3.55 vs. 3.73 to add to my 2011. I searched a ton of forums and found some really good info that I just wanted to share. I am going to upgrade because I want better times at the track dont really care about MPG's cause its not a daily for me. Anyways chime in if you like but im leaning toward 3.55's at this point...This is the info I found interesting:


Technically the redline of the new 5.0 is 6850 rpms.
Fuel cutoff is 7000 rpms.

So I'll give you the top speed in each gear at the 6850 rpm redline for 3.55's and 3.73's
If you take it the extra 150 rpms you'll get another 1-4 mph out of each gear (about 1 mph in 1st and around 4 in 5th).

3.55

1st - 42.4 mph
2nd - 63.8
3rd - 91.8
4th - 117.5
5th - 155.1
6th - 155 limiter


3.73's

1st - 40.0
2nd - 60.3
3rd - 86.7
4th - 111.1
5th - 146.6
6th - 155 limiter

I'd have to run them but off the top of my head 3.31 is about

1st - 44
2nd - 65
3rd - 95
4th - 123
5th - limiter
6th - limiter


Now do you guys see why I've said I think the 3.55's are the best gear for 1/4 mile racing, especially if you add 30-40 hp to the car?
With the 3.73's you finish the 1/4 mile right at the top of 4th as you bang into the fuel cutoff around 113 mph (which would give you a trap speed in the 111.5-112 mph range). If you have an especially strong running car and you'll need to shift to 5th to finish, and that will end up costing you time and trap speed.
Add 10-40 hp and the same story applies.

With the 3.55's you get 117 mph at 6850 and close to 119 at fuel cutoff.
That allows you stock to run the 1/4 in 4th with no problems and you should cross the line somewhere in the 6600 rpm range...right in the peak of the power range.

Further, add up to 30-40 hp and you could still get to the stripe at the top of 4th with a traps in the 116-118 mph range.

Also notice with the 3.55's you get to the 155 mph in 5th gear.
In the 3.73's you need the shift to 6th.

The reasons above are why I will most likely order my 11 GT with the 3.55's
I think they'll produce slightly better 1/4 mile times stock over the 3.73's and probably up to .2 and 1-2 mph faster than the 3.73's on a car with up to 40 hp in mods. (and could possibly still be faster with more power in mods, as 3.73 gears will offer less traction at launch and between shifts as power rises, costing time and speed).

For auto-x and track junkies, the 3.73's will probably be the best choice.

You can also see why Ford has the 3.55 gears as standard everywhere else in the world but the U.S.
As they measure 0-100 kph (62.1 mph). With the 3.55's this is achieved right at the top of 2nd gear.
The 3.31 gears offered as standard here was simply to improve the ever stricter EPA fuel economy regulations.

Im going 3:73's because with the wheel and tire i run its gonna be more like 3:63.

Makes Sence^^^

Hmmmm...I just noticed that he never says what size wheel this is based off of...He says stock but is that 18's or 19's

3:55's were my choice on stck wheels.

However since im at 415/402 HP does that mean I would be shifting to 5th on both gear sets I wonder?

Im gona say no.

I went 3.73's in my auto and love them. It pulls hard in all the gears.

Wheel size doesn't matter, tire diameter does. And I think 18s and 19s tire diameter are nearly identical

Here's my two cents worth:
For autocross, 3.73s are pretty low. The blacktop parking lots have limited traction and you'd be better served with a tall gear for more speed range in second. It can be a big deal not to have to shift.

For what little time I have on track, the 3.73s feel great. The ideal gear would likely vary from track to track and even car to car depending on how mild or wild and track dimensions. Like the 0-60 and 1/4 mile limits noted, an ideal fit would get maxxed out just at the end of the straights. Hence the big boys change individual gears AND rearend gear ratio.

The car was designed to run its best numbers stock with 3.73 and it does ... Once you start adding power.. FI I'd go 3.55 honestly. . Drive both. You'll end up buying the 3.73

^This!

If your future plans include 700+rwhp, keep the 3.55s.

If you go FI, the most popular, and sensible choice, is to go 3.31s. Just allows you so much time to stay in boost.

If you are staying naturally aspirated, but plan on nitrous, stick to 3.55s or 3.73s, 3.73s would be preferable.

You also have to consider the diameter of your tire when trying to determine speed at xxx RPM.

IMO, 3.55 is a great median between both 3.73s and 3.31s.

Raise the rev limiter to 7300 and go 3.73s problem solved.

The higher your goal HP, the less gear you need.

I have 3.73s, but the secret is getting a tall tire on the car. Yes the larger diameter will kill off some gear, but importantly the contact patch grows front to rear. My stock, untuned 3.73 M6 GT traps 114.5 without hitting the factory rev limiter in fourth gear. Tires are 28.5" tall 305/35-20 Nitto DRs. Compared to the stock 27" tall 255/40-19s, the effective gear ratio is reduced by 5.55%, making the car "geared" like it has stock tires and a 3.53 gear ratio. I think it works well in my case. Some people freak the F out when they find out what a cast 20x10 wheel weighs with a drag radial mounted on it, but this is my daily driver and I just don't care.

PS, I think gear ratio is the most overrated metric on these cars. The engines have good power at nearly all RPMs, so you don't need a lot of gear to get them into a powerband. The cars don't really seem to gain or lose a lot of ET with gear swaps so just stick with whatever it already has and save the money for more effective mods. my .02