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3.55 Gearing - Solution to Less-Effort Cruising?

3K views 16 replies 10 participants last post by  FastFord19 
#1 ·
I've had my 2014 v6 manual for about a year now and have done the standard intake/exhaust/tune modifications except headers/h-pipe changes but left the 2.73 gearing stock. Upgraded the wheels to 18x9/18x10, did standard shifter upgrades, etc.

However, I still am a little disappointed in the performance in the car. It's outstanding above 3000-3500k, a bit disappointing below that range which I think is soley due to the gearing at this point or the 3.7 itself.

My part-time daily driver/winter beater is a 4200lb 4wd 4door 2010 Jeep Liberty with a weaker 210hp/235lb 3.7 SOHC v6/4spd auto that came with 3.73s from the factory and a towing package trim. It feels more comfortable accelerating 0-40 barely touching the 2200 rpm range in normal acceleration where my 2014 v6 stang gets there faster but feels "rubberband like" accelerating from 0-40 at the same RPM range/throttle input. Basically, at low RPMs, the car performs but doesn't feel "strong" like the Jeep does and requires winding out gears more often.

Simply put, can I achieve the same torque/response feel with a 3.55 gear end ratio (recommended for the MT82 due to the short 1st gear) like my liberty has with 3.73s and get rid of the "rubber-band" acceleration feel? My goal is that the mustang effortlessly shifts through the gears without having to rev it up so much to achieve consistent performance, allowing me to cruise easier at lower rpms and keep up with varying traffic speeds better.

My experience and based on what I've read about the gear swaps on these cars says likely yes but as my Jeep is an automatic, which multiplies torque and the peak horsepower is much later in the powerband on the mustang, I'm not sure 100% to expect here. The mustang has a DOHC 3.7 with Ti-VCT so I'm not sure if below 3k rpms is it going to continue to act the same way at lower RPM ranges feeling slightly "rubber-band like/weak" compared to old-school technology like the 3.7 SOHC in the Jeep.

Thanks for any help/feedback you can provide.
 
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#2 ·
Short tube Headers, stock cats and resonators and FRPP Xpipe helped mine out, drops the power band down and is a lot more peppy in the lower RPM's. I do have 3.31s also with the performance package so the gear change to 3.55's will certainly help you out.
 
#3 ·
With a manual you can't go wrong with 3.55 or 3.73. There's only a 100rpm difference between them and depending on what tire size you're running it may not be much different. 3.73 with 28" tires and 3.55 with 27" tires are very close in terms of final ratio with tire diameter factored in.
 
#4 ·
When I had my 2012 3.7 auto I replace the 2.73 with 3.55s plus I had a aluminum driveshaft and mpt tune they did make a difference in the bottom end take off wise ...If your happy with the 3.7 and plan on keeping it you'll enjoy the gears I traded mine in for a 5.0 day and night differance ..But if you go for the gears just make sure who you choose to install them knows what they're doing ..I found that out the hard way
 
#5 ·
do the gears but note what Jek said about choosing wisely for your installer. I had 3.31 and that is the minimum. If I was swapping out I would go to 3.55 or 3.73. The lower number if you do lots of hwy. You still won't have much torque below 3500 rpm but gears will mask that....a worthwhile mod
 
#6 ·
This is something of the many things I have planned for my little pony if needed. My question is though does swapping the gear ratio affect your mpg a lot or hardly at all? With my 3.7 all stock I get 23.5avg in town and 30+mpg on the hwy. Would hate to see that go down for the sake of a few extra G's on the low end. It's my daily driver and I love how it scoots from the light without having to floor it.
 
#8 ·
AJ,

on paper you should only notice it on hwy unless you are in a top gear at other times. To conserve you will just have to be one gear higher when you are cruising around (5th instead of 4th). I doubt there will be a huge change but odds are it will go down a bit

YMMV
 
#9 ·
Regardless of the option you go with, toss in a 1 piece driveshaft. The stock 2 piece are less than desirable, especially when you increase the shaft rpm from shorter gears. If you don't upgrade I'd plan to keep it under 100 mph.

If you go 1 piece I'd also look at a driveshaft safety loop, it's good extra insurance with a 1 piece.
 
#10 ·
When I had my V6 I put in a one piece aluminum driveshaft and 3.73:1 gears. I very much enjoyed it.

But, in autocross I was forced to shift up and down, which makes for a slower lap time. My friends used 3.55:1 and never had to shift out of gear. This might have simply been a function of the track layout, but I think I would have been a little bit happier with 3.55:1 for autocross and for general driving.

That said on the bigger track, 3.73:1 was a whole lot of fun!! For that use I had no regrets. Around town, yes I did lose a couple mpg. Same on the highway (55-60). On the interstate, the loss was slightly more. Still I was getting a pleasant 27 mpg on the highway driving however I like. This is after going from the stock 2.93:1 or whatever it was down to 3.73:1.

hope this helps.
 
#11 ·
I’ve been looking at doing this too. It’s going to cost about $1,600 to do gears, driveshaft, safety loop w/installation). So it will be one of the last things we do to the car.
 
#13 ·
Went with 3.55

I went with the 3.55 mainly because my rear diff is leaking and the 3.73 are on backorder at AM. I also read some reviews where some people said the 3.73 had more noise than they liked.
Ordered all this:

3.55 Gear Kit- https://www.americanmuscle.com/355-gear-oil-kit-1014.html
Traction Lok Rebuild Kit- https://www.americanmuscle.com/ford-88-traclok-kit.html
Rear Axle Bearing & Seal Kit- https://www.americanmuscle.com/frpp-rear-bearing-kit-0514.html
Ford Performance Dif. Cover- https://www.americanmuscle.com/frpp-88-diff-cover.html
 

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#14 · (Edited)
To follow up, I had 3.55's installed (Ford Racing with the complete 8.8 Install Kit) along with a DSS 1 piece Aluminum driveshaft and Redline diff fluid & friction modifier. I took it to a performance shop that specializes in Mustangs (Evolution Performance), took them a few days to complete the work as they basically set up the gears so well that it doesn't require a break in fluid change. Did such a nice job that the gears are whisper quiet even after less than 100 miles of driving!

Overall, the difference is amazing! The car is so much more fun to drive and the torque increase was significantly noticeable. You basically have to relearn how to drive it and I've been driving manuals and high performance cars for 15 years, it's that different!

I have an intake (airraid tube, airaid tb spacer, wrapped in heat insulation tape), MPT 87 performance tune, polyurethane shifter bushing, steeda shift ball and strut bar, and borla s-types on an otherwise stock exhaust. The car simply rips and it takes little effort to accelerate now where before it was "rubberband-like" acceleration and lagged generally in moderate driving unless you were pushing it. Chirps 2nd gear with 275s (on 18x10 AMR wheels) with ease and take off from a stop is outstanding! I start in 1st gear from a stop easily and the rpms are around 2000/2100 at 65mph in 6th which is perfect.

I noticed too that the shifting feels more "connected" and there is less vibration or harshness shifting in lower RPM driving which is great. Accelerating and maintaining in just regular traffic is very easy, much easier than with 2.73s where it was hard to keep the car in the powerband and it would fall behind as speeds changed in traffic. It simply pulls in every gear now, even in 6th at low RPMs (1500 rpms).

I'll eventually switch it back to a 91/93 MPT tune but it's wild enough as is on the 87 tune for me for regular driving in the interim. In other words, if you have a 3.7 with 2.73's, do it! I was considering a 5.0 potentially but after a few easy pulls with my car (not pushing it yet, 3-4k rpm shifts) with the gears, I'm good for now lol.
 
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