Need Advice On Gear Choice, Please Help!!

Which Gears would be best for my automatic GT?

  • 3.55

    Votes: 1 33.3%
  • 3.73

    Votes: 2 66.7%

  • Total voters
    3

13 GT/CS

Member
Jul 5, 2013
36
3
9
My current setup is a 2013 Automatic GT and its a daily driver.
I am looking into getting a supercharger in the future as well but I need some advice on gear choice.
It came stock with 3.15..but I cant decide if I should go with 3.55 or 3.73. 4.10s i think are out of the question because i have heard of MPG loss and I cant afford that. All responses are appreciated and look forward to reading them, Thanks!!
 
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Husky44

Active Member
Sep 27, 2006
807
71
29
Vero Beach, FL
We can help you more if you tell us what you're trying to accomplish. Are you building a 1/4 mile car? Daily driver, with lots of highway commute miles? Stop-light terror?

FWIW, there's charts out there where you can put in your gear ratio, rear tire diameter, trans gearing, etc, and it'll spit out what your RPM readings will be at various speeds for each gear. IMHO, there's not a huge amount of difference between 3.55s and 3.73s. I'd go with the 3.73s, unless you're going to be racking up huge highway miles, and aren't as interested in street performance. I'm running 3.73s in mine with a blower, but it's a manual. Very happy with it; still well-behaved on the highway, and can net me better than 24 mpg if I drive like a nun.
 

13 GT/CS

Member
Jul 5, 2013
36
3
9
We can help you more if you tell us what you're trying to accomplish. Are you building a 1/4 mile car? Daily driver, with lots of highway commute miles? Stop-light terror?

FWIW, there's charts out there where you can put in your gear ratio, rear tire diameter, trans gearing, etc, and it'll spit out what your RPM readings will be at various speeds for each gear. IMHO, there's not a huge amount of difference between 3.55s and 3.73s. I'd go with the 3.73s, unless you're going to be racking up huge highway miles, and aren't as interested in street performance. I'm running 3.73s in mine with a blower, but it's a manual. Very happy with it; still well-behaved on the highway, and can net me better than 24 mpg if I drive like a nun.
It is a daily driver, but I would like to take it to the track on the weekends as well. Smoking some people at stoplights wouldn't be bad either. My current setup has BBK longtube headers/Off-Road Xpipe, Boss Manifold etc (but that would be removed probably next summer when I invest in a Super Charger. I hear a lot of people recommend 3.73s but I was reading somewhere about 3.55 being good for SC applications. Gears is one thing I know not much about so im clueless in the subject. Just don't want to invest and the be disappointed.
 

TheShabz

Member
Aug 4, 2012
275
18
19
Los Angeles
I'm in a similar spot with the gears with an automagic and blower in mind. I'm sure anything more than the 3.15s we have now will be great, and I don't have too many concerns over the mileage. For me, it's getting in the sweet spot for the weekend 1/4mi and canyon roads
 

Dugl

Member
May 18, 2011
83
16
19
PA.
There are guys on here that are more familiar with automatics, but I believe the autos are geared lower than the 5/6 spd manuals, so you may not have to go too aggreesive. Tire diameter makes a difference also...I lost an inch going from a 55 series to a 40 and went from a 4.10 to a 4.30 effective ratio. (28" tall slicks fix that) The other thing is that I am almost positive you will need a tuner ($400) to manage shift points and speedo calibration. (my manual is off 10 mph on the highway...my GPS is spot on) I'm also not sure at what point you may need extra cooling for the trans.
 

TheShabz

Member
Aug 4, 2012
275
18
19
Los Angeles
Yea, that's the sticking point for me. the mentality for the manuals doesn't quite jive with what an auto should have. of course, a dyno tune is in the works for when this all happens, so it's not just the speedo and shift points i'd be messing with. I've heard of people putting down 600hp on the stock trans, so it seems like it's pretty sturdy as it is.
 

Alloy08GT

New Member
Oct 19, 2013
5
0
2
49
Owensboro Ky
Just put in a set of 3.73's, haven't had them long but I can tell a big difference between the 3.31's I had for sure. Yesterday I actually got sideways in 3rd with Traction Control ON...............!!!!

(And 4 people in the car I might add)
 

BobEFFC

New Member
Sep 8, 2013
10
1
2
Detroit
Wait a minute here.. You have a 3.15 and an 8500rpm Boss manifold and an automatic..? With that setup a 4.10 (or more).
A centri I'd still probably run a 4.10 although the 3.73 would be fine too. For a daily driver with a positive displacement blower a 3.55 is plenty of gear especially if you're concerned with gas mileage.