The Mustang Forum for Track & Racing Enthusiasts

Taking your Mustang to an open track/HPDE event for the first time? Do you race competitively? This forum is for you! Log in to remove most ads.

  • Welcome to the Ford Mustang forum built for owners of the Mustang GT350, BOSS 302, GT500, and all other S550, S197, SN95, Fox Body and older Mustangs set up for open track days, road racing, and/or autocross. Join our forum, interact with others, share your build, and help us strengthen this community!

S197 Rear gear question 355 vs 373

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

105
57
Exp. Type
HPDE
Exp. Level
Under 3 Years
Nova Scotia Canada
My 2014 V6 currently has 273 rear gears. The upgrade is coming soon (ish) I just need to decide on some things.
The first thing I need to decide is which gears I want to go with, I’ll still be daily driving the car in the summer months so I wasn’t to sure about making the jump to a 410. My dad just swapped the gears in his car and had offered me his 355s gears for free.
Im mainly wondering if it would be worth spending the extra money on the 373s. Is the difference noticeable with the 373s vs the 355s.
What would the cons be for making the jump to a 410 for street driving other then the obvious fuel economy.
I assume I will need an upgraded driveshaft but I’m not sure what I should look for in that respect
 

TMSBOSS

Spending my pension on car parts and track fees.
7,615
5,385
Exp. Type
HPDE
Exp. Level
10-20 Years
Illinois
Before you start spinning the drive shaft faster. Make sure it’s safe to do so. We had a 2013 V6 and the vehicle was restricted to 115MPH from the factory. Folks who spun the factory shaft faster usually lost the drive shaft in a dramatic fashion. Are you still running the stock drive shaft?
 
105
57
Exp. Type
HPDE
Exp. Level
Under 3 Years
Nova Scotia Canada
Before you start spinning the drive shaft faster. Make sure it’s safe to do so. We had a 2013 V6 and the vehicle was restricted to 115MPH from the factory. Folks who spun the factory shaft faster usually lost the drive shaft in a dramatic fashion. Are you still running the stock drive shaft?
I am currently running the stock driveshaft but will be buying an aftermarket one and installing it at the same time I install the rear gears. I just need to figure out what to buy for an upgraded driveshaft
 
6,676
8,784
The 3.55s are stock on the GT, I have those in Superbeater and only use up to 4th gear on most tracks. (2006, 5 speed)I have a set of 3.73s on the shelf. If you have an automatic, I'd say the 3.90 to 4.10s are a no brainer. All else prolly 3.73 to 3.90s. Even so, those 3.55s will be light years faster than those 2.73s.. The SCCA calls out the 3.55s for Mustang V6, T4 cars, so they are a decent alternative.
 
1,294
1,300
Exp. Type
HPDE
Exp. Level
5-10 Years
Lenoir City TN
My 2011 GT had 3.55’s with the MT82. Gearing was decent on most tracks with 19” wheels. Probably would have been better with a little shorter wheel. If you are running 18” wheels I would try the 3.55’s. If 19’s I would probably go 3.73.
 
105
57
Exp. Type
HPDE
Exp. Level
Under 3 Years
Nova Scotia Canada
The 3.55s are stock on the GT, I have those in Superbeater and only use up to 4th gear on most tracks. (2006, 5 speed)I have a set of 3.73s on the shelf. If you have an automatic, I'd say the 3.90 to 4.10s are a no brainer. All else prolly 3.73 to 3.90s. Even so, those 3.55s will be light years faster than those 2.73s.. The SCCA calls out the 3.55s for Mustang V6, T4 cars, so they are a decent alternative.
I’ve got the 6 speed and I’m running 18 inch wheels. I’m leaning toward the 355s mainly because they are free lol…
But in the back of my mind the saying “do it right or do it twice“ is bouncing around
 
105
57
Exp. Type
HPDE
Exp. Level
Under 3 Years
Nova Scotia Canada
My 2011 GT had 3.55’s with the MT82. Gearing was decent on most tracks with 19” wheels. Probably would have been better with a little shorter wheel. If you are running 18” wheels I would try the 3.55’s. If 19’s I would probably go 3.73.
I’ve got 18 inch wheels and I will most likely be staying with 18s at least as a track set up. I think the 355s are going to be the answer
 
1,294
1,300
Exp. Type
HPDE
Exp. Level
5-10 Years
Lenoir City TN
The 3.55’s will be a huge improvement over what you are running now. And would be my choice with 18” wheels and the MT82 in a GT. Not sure about how much difference the V6 makes.
 
65
68
Exp. Type
HPDE
Exp. Level
Under 3 Years
The Central Valley of California
I am running 19x11s (295/35/ZR19s) in an Automatic 2016 V6 track car. What gears would you all suggest for me and maybe the tracloc diff upgrade? Currently running stock base model 3.15 gearing and diff.
Going full NA build.

The gearing upgrade shouldn't affect the ECU too much so I wouldn't be able to pass CARB right? (I am still learning as I go, apologies if this is a stupid question...fighting emissions crud over here.)
 
Last edited:
6,676
8,784
I am running 19x11s (295/35/ZR19s) in an Automatic 2016 V6 track car. What gears would you all suggest for me and maybe the tracloc diff upgrade? Currently running stock base model 3.15 gearing and diff.
Going full NA build.

The gearing upgrade shouldn't affect the ECU too much so I wouldn't be able to pass CARB right? (I am still learning as I go, apologies if this is a stupid question...fighting emissions crud over here.)
I'm not positive about emissions, although it doesn't seem logical that a gear change would effect emissions , unless they ran it on some type of chassis dyno. Generally, automatics like a bit more gear than a stck car, so if a 3.9 is great for a stick, a 4.1 would be good for the auto.
I would prolly go 3.70 in your case.
Now, about that auto, if you plan on running an auto on a road course, you need to get to know @flyhalf , to my knowledge, he is still the only guy to win a national championship with a slushbox.
With regards to the diff, you can find used Ford units everywhere in decent shape, they are easily rebuilt. Hit search and you'll find articles on setting up gearing on this site as well.
Most guys on this site realize people have to start someplace, so don't worry about asking dumb questions.
 
65
68
Exp. Type
HPDE
Exp. Level
Under 3 Years
The Central Valley of California
I'm not positive about emissions, although it doesn't seem logical that a gear change would effect emissions , unless they ran it on some type of chassis dyno. Generally, automatics like a bit more gear than a stck car, so if a 3.9 is great for a stick, a 4.1 would be good for the auto.
I would prolly go 3.70 in your case.
Now, about that auto, if you plan on running an auto on a road course, you need to get to know @flyhalf , to my knowledge, he is still the only guy to win a national championship with a slushbox.
With regards to the diff, you can find used Ford units everywhere in decent shape, they are easily rebuilt. Hit search and you'll find articles on setting up gearing on this site as well.
Most guys on this site realize people have to start someplace, so don't worry about asking dumb questions.

I appreciate the response, for emissions they just do the OBD scan, visual inspect, and make sure no codes. So should be perfect.

Rock on, 3.70 it is.

I talk to (read: pester with questions) him occasionally like the 20-something goof I am...will be asking him transmission cooling/other cooling questions soon...

Sweet, I wouldn't mind trying a hand at it...I have a shop who could fix my mistakes if needed haha.

Very appreciated, I love mechanics and track time...and want to learn and enjoy every moment!!! (As long as my job allows haha)
 

Dave_W

Cones - not just for ice cream
1,062
1,388
Exp. Type
Autocross
Exp. Level
20+ Years
Connecticut
With some math, you can take your track tire circumference and calculate mph at redline in 3rd and 4th gear (or 2nd gear for autocross), and also your street tire circumference and rpm at highway cruising mph. If you have a track you run at most of the time, take your apex mph for the 2 or 3 most important corners (leading to long straights / passing zones) and calculate what rpm you'd be at with each gearing - is it a good range for drive off the corner, or are you either bogging or nearly at redline?
 
6,676
8,784
With some math, you can take your track tire circumference and calculate mph at redline in 3rd and 4th gear (or 2nd gear for autocross), and also your street tire circumference and rpm at highway cruising mph. If you have a track you run at most of the time, take your apex mph for the 2 or 3 most important corners (leading to long straights / passing zones) and calculate what rpm you'd be at with each gearing - is it a good range for drive off the corner, or are you either bogging or nearly at redline?
 

TMO Supporting Vendors

Top