Which Gears Should I Get?

[muzamill_717]

Hey Guys I recently got a 96 Mustang GT 2V, and I heard one of first mods I should is a Rear Gear Change, But I thing is I be cruising around 80 or 90 MPH in the Highway (Carpool lane of course), But I want a faster acceleration, so should I get 3.55, 3.73, or 4.10??

Sincerely, Muzamil

 

[96blak54]

My 96 Gt came stock with 2.73 gears. I swapped them out in favor for 3.55. I feel like 3.55 is a good best of both worlds ratio. Youll run close to 3k rpm at around 80mph. Truth be told, if you can swap in a 6speed manual, you might not need a gear swap.

 

[muzamill_717]

My 96 Gt came stock with 2.73 gears. I swapped them out in favor for 3.55. I feel like 3.55 is a good best of both worlds ratio. Youll run close to 3k rpm at around 80mph. Truth be told, if you can swap in a 6speed manual, you might not need a gear swap.

thanks for the input.

 

[07GtS197]

I’ve had 3.55s, 3.73s, 4.10s and 4.56s. I liked both 3.73s and 4.10s. 3.55s are good if you do a lot of freeway driving, otherwise the other two.

 

[shovel]

Stock would be 2.73, 3.08 or 3.27 - do you know which you have? Is your transmission manual or automatic?

One of the things that nobody talks about with deep diff gears is the versatility of each transmission gear - if your diff ratio is 20% greater then the range of road speeds you can be in for any given transmission gear is 20% smaller. For a manual that means you're shifting more often with deeper gears and of course you're not accelerating while you shift. For an automatic it's shifting more often too you just don't get as tired of it as quickly.

Highway RPM is one thing, having to be busy while driving is another. I think 3.55 or 3.27 is the right answer for a V8 you actually drive in the real world.

I've got 3.08 in mine & changing that is within my abilities (financially) if I wanted - but I'm keeping it how it is. I've changed final gear in a few other vehicles over the years and sometimes it was the right answer, occasionally it wasn't and I learned something.

 

[muzamill_717]

Stock would be 2.73, 3.08 or 3.27 - do you know which you have? Is your transmission manual or automatic?

One of the things that nobody talks about with deep diff gears is the versatility of each transmission gear - if your diff ratio is 20% greater then the range of road speeds you can be in for any given transmission gear is 20% smaller. For a manual that means you're shifting more often with deeper gears and of course you're not accelerating while you shift. For an automatic it's shifting more often too you just don't get as tired of it as quickly.

Highway RPM is one thing, having to be busy while driving is another. I think 3.55 or 3.27 is the right answer for a V8 you actually drive in the real world.

I've got 3.08 in mine & changing that is within my abilities (financially) if I wanted - but I'm keeping it how it is. I've changed final gear in a few other vehicles over the years and sometimes it was the right answer, occasionally it wasn't and I learned something.

I got a 5 speed manual it’s like 2350-2400 rpm when on 5 gear when going 85 mph

 

[shovel]

I got a 5 speed manual it’s like 2350-2400 rpm when on 5 gear when going 85 mph

If nobody's changed the gears already then there should be a tag hanging on your diff cover with the ratio, since all GT's got limited slip it would read something like "3L08" or "3L27"

There are also plenty of gear ratio calculators scattered around the internet to estimate ratio/mph/rpm if you don't have that tag or can't get under the car.

 

[muzamill_717]

If nobody's changed the gears already then there should be a tag hanging on your diff cover with the ratio, since all GT's got limited slip it would read something like "3L08" or "3L27"

There are also plenty of gear ratio calculators scattered around the internet to estimate ratio/mph/rpm if you don't have that tag or can't get under the car.

thanks

 

[RAU03MACH]

373 are about the middle for gas saving and power

 

[badass98svt]

On a 2V, I'd recommend 3.73

Never fear the gear

 

[cobrajeff96]

Highest numerical gear for stock trans and stock power would be 3.73 in my opinion. If you're increasing power 100hp or more, 3.55s would be better if you still drive it the way you do on street/highway. Of course the higher gear ratio will make the car accelerate noticeably quicker at the expense of top speed. At max desired speed, you want the motor cruising at 3k rpm or less. Anywhere from 2 to 3 is the target for cruising.

 

[Mustang5L5]

I'm the outlier here. I like my 3.27's. I have no desire to change them. If i had 2.73's or 3.08's, and i were to spend the money i'd probably go 3.55's.

I've driven 4.6L's with 3.73's, 4.10's and 4.56's and just not a fan of them for daily driving. Since my racing days are behind me, I prefer the taller gears.

I have 3.73's in my modified Fox body. I know it’s not apples to apples comparison. 1st gear is useless at this point. It’s either a burnout gear, or I’m running it to redline (casually) and shifting to 2nd just to clear an intersection driving normally. I might change to a TKX and reevaluate my hearing then, but I might step down to a 3.31 gear in that car. It’s got enough HP and is light enough that it can probably use a taller gear…especially if I add the supercharger

 

[96blak54]

Oh....a 3.31 ratio and a 3rd gear pull...nice. And then low rpm 80mph interstate cruise.

If you had 4.10 at 80mph interstate cruise, the engine sound like

WAAAAAAAAAAAAAAAAAAAAAAAAH.......in overdrive

 

[Terrorist 5.0]

There is no answer to this question. It completely depends on the person. If you are talking strictly for the 1/4 mile, then it gets easier to decide. I have a 3.08 and am going to be going to 3.31 in the future. With a 0.68 overdrive and stock tire size, that puts me at about 1830 RPM going 62 MPH. I would imagine that I wouldn't really feel the difference in traffic as much as I would when really giving it, which is exactly what I want. I have a 302 under the hood so it is a different animal entirely, and the best they came with was a 3.08 axle with the manual cars. The 4.6 cars either came with a 2.73 or a 3.27 with the manual cars. One way to tell is look at your door sticker. Under the axle section, an M will denote a 2.73, a Z will denote a 3.08, and an E will denote a 3.27. If your car is stock, I would suggest no more than a 3.27/3.31 if you want to drive it everyday. It keeps your RPM at an acceptable level when cruising, and gives good acceleration. If you are coming from smaller cars with smaller engines where you need to keep the RPM up just to keep up with traffic, you may feel differently.

One thing I would like to mention that almost everybody neglects is that you are not using 5th gear to go fast. It is too big a gap. So you are using 1st to 4th. Depending on how fast you like going, gears can cut your fun short really quick. Personally, I like to get up to about 100 MPH before letting off, but my rule of thumb is I like to be able to get up to 120 MPH without shifting to 5th or holding the RPM at an uncomfortable level. With stock size tires in my case (3.08), I am at 4850 RPM at 120 MPH. For you, with a 2.73 axle, you will be at 4300 RPM. If you have a 3.27 axle, you will be at 5150 RPM. Our engines, whether 5.0 or 4.6, can handle this RPM, but do you really want to hold it there? Especially a 5.0. They don't make any power there.

Since you said you are going to be cruising at 80 to 90 MPH, I wouldn't change anything if you have a 3.27 axle. Your RPM is already pretty high.

Just fruit for thought.

 

[Wood's 5.0]

From your description of intended highway speeds, IMO, 3:55s. Otherwise, as @96blak54 wrote...

the engine sound like

WAAAAAAAAAAAAAAAAAAAAAAAAH.......in overdrive

 

[shovel]

There's also a factor of value for cost, unless you've simply got abundant money and the cost is immaterial to the outcome. What's the value of changing from 3.27 to 3.31 for example? It's a 1.2% change so you get 1.2% more torque to the wheels in any given gear and your engine rpm is 1.2% higher at any given gear/road speed and your versatility in each gear is 1.2% less. Most people would probably agree it's just not worth the cost and effort to change from 3.27 to 3.31.

3.55 is also an option and if you go from 3.27 to 3.55 the difference is ~8.5% which is certainly more than 1.2% but still not huge. If you were specifying the car from brand new, or having an axle built anyway there might be an argument to go 3.55 if acceleration (from any gear without necessarily downshifting) is the objective because there is no added cost to choose another ratio. If you're starting from 3.27 and would have to spend the money to do 3.55's for no other reason than just the gear change it might not really be worth it.

On the other hand you could tell yourself OK 8.5% isn't worth it let's go more, 3.73 is 14% more than 3.27.. but if 3.73 starts to introduce new compromises it might end up being actually worse and then you've spent money to be worse.

If you started from 2.73 I think most would agree that for this particular platform, this particular engine that ratio is on the shallow side and unless you're pulling every gear to redline every time you shift you're spending a lot of time outside the power band. If you go from 2.73 to 3.27 that's a 20% difference. Going from 2.73 to 3.55 is a 30% difference. Just to put all the numbers out there 3.08 to 3.27 is 6% and 3.08 to 3.55 is 15% and 3.08 to 3.73 is 21% .

When I swapped the axle on my wife's 02 V6 I found a Mach 1 axle with 3.55 gears, which is 8.5% deeper than the 3.27's she had. It's subtle enough that I doubt most casual drivers would even notice if the change was made in secret. But her V6 came with an open differential & no quad shocks so installing that axle supplied a LSD, it supplied the improved "Cobra" rear brakes, it supplied quad shocks and it supplied the subtle gear change. I already had a tuner that could update its speedometer for the ratio change. That means in the context of all those improvements the actual ratio change was pretty much free. I wouldn't have done all that work if the only thing that changed was the ratio.

My 94 GT breathes a bit better than stock (MAF delete, 70mm TB, Cobra intake, 1.72 rockers, headers/midpipe/exhaust) and I suppose if it was absolutely free a change from 3.08 to 3.27 might optimize it in certain situations but it would have almost no effect on actual driving enjoyment so I just can't be bothered.

 

[badass98svt]

As far as a lower (numerically) gear giving you better mpg, I say that is bs.
I picked up MPG around town when I originally went from 3.27 to 4.30. You are in 4th gear, rather than 3rd gear. Car is at lower RPMs when cruising around town.
If you do a lot of highway driving, that would be different. Around town though my mileage definitely increases with 4.30s. Hell even on the highway I would get 20 MPG.

 

[ju015dd]

I had 410s put in my mystic back in the day. If I had a other sn95 that would be one of my first mods.

 

[Terrorist 5.0]

As far as a lower (numerically) gear giving you better mpg, I say that is bs.
I picked up MPG around town when I originally went from 3.27 to 4.30. You are in 4th gear, rather than 3rd gear. Car is at lower RPMs when cruising around town.
If you do a lot of highway driving, that would be different. Around town though my mileage definitely increases with 4.30s. Hell even on the highway I would get 20 MPG.

Yes you can get an increase in MPG around town with a ring and pinion change. The engine doesn't have to work as hard to get up to speed because it doesn't have to lug through low RPM as long. The highway MPG can actually get better too, depending on the speed. The best way to monitor any change would be either to monitor engine vacuum during driving (U-Haul trucks have that as a measure to help the average person save fuel), or to monitor the TPS readings as you drive. The higher the vacuum/lower the TPS reading, the better fuel economy you can get. On a personal note, I ride around in 4th all the time with my 3.08 axle. I keep RPM at about 1200-1300 RPM and just rest my foot on the pedal. Keeps the car quiet, and I get great fuel economy (relative to other SN95 cars).

 

[shovel]

Every engine has a different BSFC map which dictates what fuel efficient cruising looks like.

When it's engineered holistically as the manufacturer will do then low RPM means less friction (same friction per revolution x fewer revolutions = less friction per time interval) and low RPM/low throttle aperture means higher VE than higher RPM/same or less throttle aperture. That's universal on internal combustion engines, whatever tuning the OE does to depart from this is for other objectives like performance metrics & driveability.

Cars that have been modified can have wildly different BSFC characteristics, we can make armchair predictions about which ones will get optimal MPG at what cruising RPM but I don't think anyone is driving a 30 year old V8 hoping to hypermile it.