What gears would be best for my 1997 mustang gt, 3.55s or 3.73s. I will be driving on the highway from time to time. How big of a difference is it between the 2?
Which tranny do you have? Adding data about the car to your sig or profile will help folks help you. If you have an AOD, the question of gears usually gets expanded to include such things as mods to the tranny and stall converters.
The short answer imo (and there are at least a thousand other opinions equally valid around here):
1. Stock gears if you plan a postive displacement supercharger (ie, KenneBell or other roots-type) UNTIL you see how you like all that low end torque. Maybe 3.55 gears after.
2. 3.73 gears for a daily driver or a car that rarely sees a track or is NOT oriented toward 1/8 or 1/4 mile action.
3. 3.90 gears if 4.10's are a bit much.
4. 4.10 gears for drag strips and serious street machines.
5. 4.30+ gears for the strip.
6. LOL, I'll throw this one in for the "what about gas mileage" angle: "Forgedaboudit" gears for those who are searching under the couch for spare change for gas money. You don't need gears, you need a job.
__________________
tripleblack
"You can never be free until you let yourself go."
Lol its not the gas i'm worried about, how high the car is revving and how noisy it will be on the highway.
How high it revs is dependent on the size wheels and tires you are running as well...
Assuming 17" wheels, probaby 26" diameter tires.
Revs are also TOTALLY dependent on which gear and which tranny we are talking about.
If you do most of your driving in town, stop and go, the 4.10 gears will make first gear essentially go away - you will be geared low enough to where 2nd will feel like 1st, and you will be in 4th where you used to be in 3rd, etc. 5th will be more commonly used on surface roads, and running long trips on the interstate at 75mph will be a lot different.
"Noise" will be less of an issue if the gears are correctly (ie, professionally) installed than your exhaust, which WILL be louder as you run more revs of course.
This is all a subjective topic.
Find a friend (join a Mustang Club, the MCA site is Mustang Club of America , not sure) with gears and take a spin in his car.
I like the 3.73's for a daily driver. The new 08 Bullitts come with 3.73's, and I think its a great gear for the 4.6 cars, in general.
The 4.10's are for those who really like to snap passenger's necks and play stoplight bandit.
4.30's for the more serious folks running on the strips.
Final suggestion:
PLAN what you want from the car. Many mods don't play well with the other children. UDP's, intakes and often CAI's go away if you add a blower - headers are surplus with a turbo kit - and gears are dependent on things like power adders and camming and use (street, strip or road course).
Ah well.
LOL, sometimes I just wonder why I don't just say:
"4.10's are the ultimate answer to everything".
Its not true, but it would save some time!
Hey guys, look up and down a couple pages - there are several threads about gears, including several where I've posted up some semi-heavy math to play with to determine revs, etc.
__________________
tripleblack
"You can never be free until you let yourself go."
Well i do plan on getting cams, so gears would go good with that?
Probably. Most cams are designed around a certain rpm band where they generate the most power.
A typical street cam will cut in low, yielding good power for the cut and thrust, stop and go driving a street car has to cope with. Comp Cams 262 grind is the one I usually recommend for daily drivers. Power comes in at 1200rpm, and stays to 5200, yielding a nice gain over the stock cams, without sacrificing driveability or low end torque.
Their 270's are the street/strip solution, and come in at a higher rpm and extend past the normal rev range of a DD 4.6. They're about the most cam you can buy without reworking the pistons. These cams also have a rougher idle than stock. Just a bit "lumpy".
With the 270's (or stronger), lower gears help compensate for the loss of low end torque, and match the new power curve better than the stock gearing.
AGAIN, cams should be part of the plan, and will VARY depending on the other modifications made.
Best we never forget: We're building CARS, not just a motor. Add a bunch of power here - and you have to start looking at brakes, tranny, clutch, lower control arms, etc, etc, etc.
__________________
tripleblack
"You can never be free until you let yourself go."
Ya ive already been looking into the brembo gran turismos or baer. I didn't want to go that expensive but i think im gunna have to.
I was thinking about the stage 2 comp cams which are the 270s along with heads. Does that sound pretty good?
The 270 starts bringing in power at higher revs, and extends the power bandwidth to higher revs. Unless you rebuild the bottom (forged parts, rods, pistons, etc.), don't raise the rev limit on the motor. You'll just blow it up.
3.73 or higher gears would work well with that cam.
Those are good brakes you are looking at. I would still suggest you buy the Cobra kit rather than just swap in new rotors. The upgraded calipers and ss lines will stop you quicker, and are better than the stock brakes in every way.
Baer, Stoptech, SSBC, and the various kits from the tuners (Saleen, Roush, Shelby, etc.) are also excellent brakes. Hard to go wrong with any of the brand names.
__________________
tripleblack
"You can never be free until you let yourself go."
3:73s or higher is my recomendation. I'm planning 4:10s for my Bullitt and am not worried about mileage because its a Mustang, not an economy car. Some that go the 4:10 route get better mileage because the engine is not lugged down, its in its sweet spot. On a side note my old modded 97 Gt had the 3:73s and I still 26 mpg highway....
__________________
DHG #01434 Bullitt - full JLT intake, MGW shifter, Accel coils (I wish I had 4.10s, o/r H, tune)
Black 89 LX(the drag car) best 8.75 at 80 mph in the 1/8
97 Mountaineer V8 AWD
"Higher gears will lower your top speed" No, no, no. The top achievable speed for your car is determined by your engine's ability to press against the resistance caused by wind; NOT your gear ratio.
Theoretically, your "ignore wind resistance" top speed will be reduced, but unless you plan on ever reaching 186 mph don't worry about it (mid 7 1/4 mile)
With the stock gears on a stock engine (forget about bolt on crap because in reality it doesn't do much), your car will top out shortly after shifting to your last gear. You're not in your car's power band anymore and therefore cannot push against the wind. Switch to a steeper gear and yes, your RPMS will be higher but your car can continue to push against the wind.
Therefore your top achievable speed is going to increase. (this is not true with extremely steep gears such as those greater than 4.56)
"Higher ratio gears will kill your gas mileage" This is a load of crap. People claim their gas mileage suffers because they can't keep their foot out of the gas pedal. IF you drive normally, you will probably keep the same fuel economy or actually gain some.
On the highway, with the stock 3.27s, I saw 2000 rpms for 65 mph. When I got the 4.10s installed I saw 2400-2500 rpms for 65 mph. You may lose a tiny bit of fuel economy on the highway but it will be made up for off the highway.
Remember, with higher ratio gears, you will be able to get into the higher gears sooner. Instead of cruising around in 2nd or 3rd on backroads, you can cruise in 4th or 5th without stalling the engine.
"I'm afraid I'll blow my engine since steeper gears make you rev higher." Steeper gears do not make you rev higher- that's a conscious decision made by the driver. You won't blow your engine unless you abuse it.
"I want my car to accelerate fast but I don't want to lose my top speed."
Again, your top achievable speed will probably be increased. You will have higher rpms but that simply translates to more push against the wind = higher achievable top speed.
If you want to retain a low gear ratio yet want more acceleration, save up and buy a power adder such as nitrous, supercharger, or turbo.
"I want to accelerate faster but I heard that gears make it hard for you to hook."
This is a good question. In order to move, you must be able to get power to the ground. In order to get power to the ground, you need your tires to grab the road. If the torque coming from your tires onto the ground exceeds the static coefficient of friction, your tires will spin until they heat up and the torque matches or is lower than the new μs. (remember that heat increases friction for most surfaces that do not change state of matter).
So, what you need to consider is this: If you are looking at gears, you obviously like performance. Take a look at your wheels and tires and decide whether you want looks or power. If you want looks, keep your shiny wheels and buy the stickiest drag radial you can find. If you want power, say goodbye to your 18" attention-grabbers and buy some drag wheels. Sure, they don't have the same look, but who cares about how shiny your wheels are? What matters to you at this point is how much power you can get to the ground.
If you get drag tires, you will undoubtedly get more power to the ground than without them. At this point in time, you should take a look at everything else in-line to your tires. You can easily snap an axle, destroy your transmission, or even blow your engine if too much resistance is felt along your drivetrain. You will not be able to pull a high wheelie on stock drivetrain elements.
"I've heard that brand X whines and brand Y doesn't." Do you want gears or not? The amount of whine is determined by the amount of backlash (click here for a picture) given when the gears are installed. If your gears whine like crazy, they were probably installed wrong. If your gears whine once in a while and quietly, don't worry about it. If you gears only whine when you are accelerating/decelerating/coasting, you might have a faulty bearing.
Brand really does not have an impact on the amount of whine. The most common brands are Motive, Richmond, and FRPP. All three are high quality and you won't have any problem if they are installed right.
"Is there a break-in period with gears?" Absolutely. When you get your gears installed, you need to take it easy. Some people say that there is a 500-mile break-in period while others say that several warm-up and cool-down cycles are all it takes.
Here's what you do: When you get your gears installed, drive easy for 5 miles. Stop and get something to eat. Drive for another 5 miles to a mall or something. Look around for an hour. Then drive for another 5 miles. Do something that takes an hour or two.
What you are doing is allowing the gears to heat up and cool down. This tempers them and makes them incredibly hard.
10 cycles should be fine. Some say less, but to be safe, 10 cycles is fine.
"Do I need a bearing kit?" Yes and no. It never hurts to replace the bearings, however you need to be sure you're getting the right ones. If your car has low miles, you can probably skip it. If your car has moderate-high miles, it's strongly recommended.
"What is this '3.73' '4.10' and all the other numbers about?" That would be the ratio of teeth on the ring to the number of teeth on the pinion. Basically, when the engine completes a cycle, that rotation is translated to another in your transmission. Your transmission has gear ratios for every gear that's in it. The transmission output is transfered along the driveshaft and into the differential. Here, the rotation reaches the rear gears. Stock gears are typically 3.27 or 3.55. Basically, that means that for every 3.27 or 3.55 rotations provided by the transmission, your tires will spin once.
Now you can see why higher gear ratios allow you to accelerate faster. More power can get to the ground within the same revolution.
"Can I install gears myself." Sure. Why not? You need the right tools to do so and unless you have someone there to help you, you might have a difficult time. I recommend allowing a professional to install them unless you are very familiar with how the differential works and are mechanically inclined.
"What does installation cost?" This depends on where you go. Some places have work rates of 50$/hr. Some places have rates of 75$/hr.
Generally, installing gears takes 6-8 hours.
If you get a bearing kit, it will be slightly longer.
This depends greatly on how experienced the mechanic is and the condition of the existing bearings.
I paid 400$ to have mine installed with new bearings.
"4.10s are too much" Too much for what? 4.10 is one of a few ideal ratios for a modular 4.6l engine.
"Ok, 4.10s are too much for a car using a power-adder" No. 4.10s work excellent on both N/A cars and cars with forced induction. What determines whether the gears are "too much" is your ability to get the power to the ground. In which case, you should strongly consider getting stickier tires. If need be necessary, get drag tires.
There are DOT approved drag tires.
"Ok, what about 4.30s?" Again, 4.30s will not be an issue if you have a means to get the power to the ground. Even people with 4.56s can run a power adder and get the power to the ground with the right tires.
"Wow, 4.56s? How would that work on an N/A car?" Fine. You'll run high rpms on the highway but unless you have a lead foot your car will be just fine. It all depends on what you plan on doing.
"What do you recommend for gears?" There is no "right gear ratio." Every ratio has an advantage and a disadvantage. You can keep your stock gears, throw on a power-adder and do just fine. Or, you can get 4.10s, accelerate like a bat out of hell, upgrade to some sort of power adder, and do just fine.
Overall, I and many others find that 4.10s are ideal.
"Why 4.10s? I know lots of people with 3.73s" Again, you must choose between performance and drive-ability. People who choose 3.73s probably thought that 4.10s are too steep. That's fine. 3.73 will provide additional acceleration over the stock gears. Some people who purchase 3.73s have later swapped them out for 4.10s.
Some people with 4.10s have swapped them out for 4.30s.
"What kind of gain can I get with higher gear ratios." The jump from 3.27s to 4.10s will get you 25% more rpms at any given speed.
This translates to greater acceleration regardless of rpm/gear and may result in a higher achievable rpm.
Performance gains (number-wise) are determined by what you have done to the car. Some people claim that you are trading horsepower for torque, but that is untrue. In reality, you are gaining both if you get the ideal ratio for your engine's output. *cough 4.10 cough*
"What if I have a Cobra." Same thing, but since you have a 4V cam assembly, you have your choice of 4.10s and 4.30s for ideal ratios.
Gears work in concert with other variables (including aerodynamic factors, as dawrr points out) to deliver power to the rear wheels. Higher gears MIGHT lower your top speed, depending on how much they mis-match the camming of the motor - the use of the car (quarter mile warrior or daily commuter or road course or autobahn screamer or salt flats top speed record run, etc, etc, etc) - and yes, the aerodynamic and suspension limits of the design.
A balanced design has a motor cammed, fueled and built to match the rpm's needed to meet the demands put upon it by the owner. Over-camming a car with weak gears just makes it hard to drive and a poor-performer (for its design). Over-gearing a car with a weak cam is essentially the same sort of sin, in which the car would do better were it properly set up and everything matching as it should be. Cost becomes the usual limiting factor (swapping in cams is not cheap, whereas gears are relatively easy).
Making a strong change in one area may tilt a car design off its balanced axis. Milder gears match well with the low end torque of the roots/twin screw blower motors, because the whole purpose is to match the torque output to available traction. Adding tons of gear to a car that will split its LCA bushings or toss IRS half shafts (all things that have happened in reality) the first time its pressed is an equally bad idea.
Stock or near-stock 4.6 powered GT's do NOT have a problem of "too much torque", and handle a good amount of gear without losing all traction or control, or spitting out major broken components.
3.27, 3.55, 3.73, 3.90 4.10, 4.30, etc. gears all have their uses and fans, and they all will work in our cars.
Since the title of this topic is "Which gears for highway?", the answer would be something other than a gear selection designed to maximize quarter mile acceleration or even stop and go driving. Highway cruising requires a good overdrive, which these 5 speeds provide. Raising engine speed 400-500 rpms WILL be perceptible, and only the user can determine whether or not this is objectionable. Rpm's also translate directly into gas mileage, so adding 10% more rpm's to a trip will yield about 10% lower gas mileage, and I have witnessed this as the usual result of going from stock gearing to 4.10's.
10% is a real difference, but is it a CRUCIAL difference?
Even at $3 per gallon, the typical driver driving 15000 miles per year and getting 20mpg would be using 750 gallons of fuel per year, or $2250 worth of gas. 10% would add $225 to the fictional driver's gas bill, or put another way, about $4 per week.
Most of us would not notice a $4 per week penalty, whereas we WOULD notice the effect of the gearing!
Perspective and balance. All the hallmarks of a good car build.
Higher gears always extract a small penalty in terms of gas mileage, net, but the driving habits and routines of the owner make a much stronger impact.
Engine camming is the classical origin of gear match thinking. Comp Cams has a new line of gas sipping econo grinds that harken back to the 80's and early 90's for the V8's, when 2.xx gears were the norm, and cams were designed for "efficiency" rather than power. I look for this to happen again, given the new CAFE rules coming down the pike. Buy stock in the cam companies - in the future, cam swaps might rival loud exhausts as the first upgrade people do to their new cars.
Quote:
Originally Posted by dawrr
Let me dispel some common myths:
"Higher gears will lower your top speed"
No, no, no. The top achievable speed for your car is determined by your engine's ability to press against the resistance caused by wind; NOT your gear ratio.
Theoretically, your "ignore wind resistance" top speed will be reduced, but unless you plan on ever reaching 186 mph don't worry about it (mid 7 1/4 mile)
With the stock gears on a stock engine (forget about bolt on crap because in reality it doesn't do much), your car will top out shortly after shifting to your last gear. You're not in your car's power band anymore and therefore cannot push against the wind. Switch to a steeper gear and yes, your RPMS will be higher but your car can continue to push against the wind.
Therefore your top achievable speed is going to increase. (this is not true with extremely steep gears such as those greater than 4.56)
"Higher ratio gears will kill your gas mileage"
This is a load of crap. People claim their gas mileage suffers because they can't keep their foot out of the gas pedal. IF you drive normally, you will probably keep the same fuel economy or actually gain some.
On the highway, with the stock 3.27s, I saw 2000 rpms for 65 mph. When I got the 4.10s installed I saw 2400-2500 rpms for 65 mph. You may lose a tiny bit of fuel economy on the highway but it will be made up for off the highway.
Remember, with higher ratio gears, you will be able to get into the higher gears sooner. Instead of cruising around in 2nd or 3rd on backroads, you can cruise in 4th or 5th without stalling the engine.
"I'm afraid I'll blow my engine since steeper gears make you rev higher."
Steeper gears do not make you rev higher- that's a conscious decision made by the driver. You won't blow your engine unless you abuse it.
"I want my car to accelerate fast but I don't want to lose my top speed."
Again, your top achievable speed will probably be increased. You will have higher rpms but that simply translates to more push against the wind = higher achievable top speed.
If you want to retain a low gear ratio yet want more acceleration, save up and buy a power adder such as nitrous, supercharger, or turbo.
"I want to accelerate faster but I heard that gears make it hard for you to hook."
This is a good question. In order to move, you must be able to get power to the ground. In order to get power to the ground, you need your tires to grab the road. If the torque coming from your tires onto the ground exceeds the static coefficient of friction, your tires will spin until they heat up and the torque matches or is lower than the new μs. (remember that heat increases friction for most surfaces that do not change state of matter).
So, what you need to consider is this: If you are looking at gears, you obviously like performance. Take a look at your wheels and tires and decide whether you want looks or power. If you want looks, keep your shiny wheels and buy the stickiest drag radial you can find. If you want power, say goodbye to your 18" attention-grabbers and buy some drag wheels. Sure, they don't have the same look, but who cares about how shiny your wheels are? What matters to you at this point is how much power you can get to the ground.
If you get drag tires, you will undoubtedly get more power to the ground than without them. At this point in time, you should take a look at everything else in-line to your tires. You can easily snap an axle, destroy your transmission, or even blow your engine if too much resistance is felt along your drivetrain. You will not be able to pull a high wheelie on stock drivetrain elements.
"I've heard that brand X whines and brand Y doesn't."
Do you want gears or not? The amount of whine is determined by the amount of backlash (click here for a picture) given when the gears are installed. If your gears whine like crazy, they were probably installed wrong. If your gears whine once in a while and quietly, don't worry about it. If you gears only whine when you are accelerating/decelerating/coasting, you might have a faulty bearing.
Brand really does not have an impact on the amount of whine. The most common brands are Motive, Richmond, and FRPP. All three are high quality and you won't have any problem if they are installed right.
"Is there a break-in period with gears?"
Absolutely. When you get your gears installed, you need to take it easy. Some people say that there is a 500-mile break-in period while others say that several warm-up and cool-down cycles are all it takes.
Here's what you do: When you get your gears installed, drive easy for 5 miles. Stop and get something to eat. Drive for another 5 miles to a mall or something. Look around for an hour. Then drive for another 5 miles. Do something that takes an hour or two.
What you are doing is allowing the gears to heat up and cool down. This tempers them and makes them incredibly hard.
10 cycles should be fine. Some say less, but to be safe, 10 cycles is fine.
"Do I need a bearing kit?"
Yes and no. It never hurts to replace the bearings, however you need to be sure you're getting the right ones. If your car has low miles, you can probably skip it. If your car has moderate-high miles, it's strongly recommended.
"What is this '3.73' '4.10' and all the other numbers about?"
That would be the ratio of teeth on the ring to the number of teeth on the pinion. Basically, when the engine completes a cycle, that rotation is translated to another in your transmission. Your transmission has gear ratios for every gear that's in it. The transmission output is transfered along the driveshaft and into the differential. Here, the rotation reaches the rear gears. Stock gears are typically 3.27 or 3.55. Basically, that means that for every 3.27 or 3.55 rotations provided by the transmission, your tires will spin once.
Now you can see why higher gear ratios allow you to accelerate faster. More power can get to the ground within the same revolution.
"Can I install gears myself."
Sure. Why not? You need the right tools to do so and unless you have someone there to help you, you might have a difficult time. I recommend allowing a professional to install them unless you are very familiar with how the differential works and are mechanically inclined.
"What does installation cost?"
This depends on where you go. Some places have work rates of 50$/hr. Some places have rates of 75$/hr.
Generally, installing gears takes 6-8 hours.
If you get a bearing kit, it will be slightly longer.
This depends greatly on how experienced the mechanic is and the condition of the existing bearings.
I paid 400$ to have mine installed with new bearings.
"4.10s are too much"
Too much for what? 4.10 is one of a few ideal ratios for a modular 4.6l engine.
"Ok, 4.10s are too much for a car using a power-adder"
No. 4.10s work excellent on both N/A cars and cars with forced induction. What determines whether the gears are "too much" is your ability to get the power to the ground. In which case, you should strongly consider getting stickier tires. If need be necessary, get drag tires.
There are DOT approved drag tires.
"Ok, what about 4.30s?"
Again, 4.30s will not be an issue if you have a means to get the power to the ground. Even people with 4.56s can run a power adder and get the power to the ground with the right tires.
"Wow, 4.56s? How would that work on an N/A car?"
Fine. You'll run high rpms on the highway but unless you have a lead foot your car will be just fine. It all depends on what you plan on doing.
"What do you recommend for gears?"
There is no "right gear ratio." Every ratio has an advantage and a disadvantage. You can keep your stock gears, throw on a power-adder and do just fine. Or, you can get 4.10s, accelerate like a bat out of hell, upgrade to some sort of power adder, and do just fine.
Overall, I and many others find that 4.10s are ideal.
"Why 4.10s? I know lots of people with 3.73s"
Again, you must choose between performance and drive-ability. People who choose 3.73s probably thought that 4.10s are too steep. That's fine. 3.73 will provide additional acceleration over the stock gears. Some people who purchase 3.73s have later swapped them out for 4.10s.
Some people with 4.10s have swapped them out for 4.30s.
"What kind of gain can I get with higher gear ratios."
The jump from 3.27s to 4.10s will get you 25% more rpms at any given speed.
This translates to greater acceleration regardless of rpm/gear and may result in a higher achievable rpm.
Performance gains (number-wise) are determined by what you have done to the car. Some people claim that you are trading horsepower for torque, but that is untrue. In reality, you are gaining both if you get the ideal ratio for your engine's output. *cough 4.10 cough*
"What if I have a Cobra."
Same thing, but since you have a 4V cam assembly, you have your choice of 4.10s and 4.30s for ideal ratios.
I hope this helped.
__________________
tripleblack
"You can never be free until you let yourself go."
This is a straight forward and informative thread dude. I have a 96 GT 5-speed and wanna do gears, and this was a huge help. Thanks dawrr
Quote:
Originally Posted by dawrr
Let me dispel some common myths:
"Higher gears will lower your top speed"
No, no, no. The top achievable speed for your car is determined by your engine's ability to press against the resistance caused by wind; NOT your gear ratio.
Theoretically, your "ignore wind resistance" top speed will be reduced, but unless you plan on ever reaching 186 mph don't worry about it (mid 7 1/4 mile)
With the stock gears on a stock engine (forget about bolt on crap because in reality it doesn't do much), your car will top out shortly after shifting to your last gear. You're not in your car's power band anymore and therefore cannot push against the wind. Switch to a steeper gear and yes, your RPMS will be higher but your car can continue to push against the wind.
Therefore your top achievable speed is going to increase. (this is not true with extremely steep gears such as those greater than 4.56)
"Higher ratio gears will kill your gas mileage"
This is a load of crap. People claim their gas mileage suffers because they can't keep their foot out of the gas pedal. IF you drive normally, you will probably keep the same fuel economy or actually gain some.
On the highway, with the stock 3.27s, I saw 2000 rpms for 65 mph. When I got the 4.10s installed I saw 2400-2500 rpms for 65 mph. You may lose a tiny bit of fuel economy on the highway but it will be made up for off the highway.
Remember, with higher ratio gears, you will be able to get into the higher gears sooner. Instead of cruising around in 2nd or 3rd on backroads, you can cruise in 4th or 5th without stalling the engine.
"I'm afraid I'll blow my engine since steeper gears make you rev higher."
Steeper gears do not make you rev higher- that's a conscious decision made by the driver. You won't blow your engine unless you abuse it.
"I want my car to accelerate fast but I don't want to lose my top speed."
Again, your top achievable speed will probably be increased. You will have higher rpms but that simply translates to more push against the wind = higher achievable top speed.
If you want to retain a low gear ratio yet want more acceleration, save up and buy a power adder such as nitrous, supercharger, or turbo.
"I want to accelerate faster but I heard that gears make it hard for you to hook."
This is a good question. In order to move, you must be able to get power to the ground. In order to get power to the ground, you need your tires to grab the road. If the torque coming from your tires onto the ground exceeds the static coefficient of friction, your tires will spin until they heat up and the torque matches or is lower than the new μs. (remember that heat increases friction for most surfaces that do not change state of matter).
So, what you need to consider is this: If you are looking at gears, you obviously like performance. Take a look at your wheels and tires and decide whether you want looks or power. If you want looks, keep your shiny wheels and buy the stickiest drag radial you can find. If you want power, say goodbye to your 18" attention-grabbers and buy some drag wheels. Sure, they don't have the same look, but who cares about how shiny your wheels are? What matters to you at this point is how much power you can get to the ground.
If you get drag tires, you will undoubtedly get more power to the ground than without them. At this point in time, you should take a look at everything else in-line to your tires. You can easily snap an axle, destroy your transmission, or even blow your engine if too much resistance is felt along your drivetrain. You will not be able to pull a high wheelie on stock drivetrain elements.
"I've heard that brand X whines and brand Y doesn't."
Do you want gears or not? The amount of whine is determined by the amount of backlash (click here for a picture) given when the gears are installed. If your gears whine like crazy, they were probably installed wrong. If your gears whine once in a while and quietly, don't worry about it. If you gears only whine when you are accelerating/decelerating/coasting, you might have a faulty bearing.
Brand really does not have an impact on the amount of whine. The most common brands are Motive, Richmond, and FRPP. All three are high quality and you won't have any problem if they are installed right.
"Is there a break-in period with gears?"
Absolutely. When you get your gears installed, you need to take it easy. Some people say that there is a 500-mile break-in period while others say that several warm-up and cool-down cycles are all it takes.
Here's what you do: When you get your gears installed, drive easy for 5 miles. Stop and get something to eat. Drive for another 5 miles to a mall or something. Look around for an hour. Then drive for another 5 miles. Do something that takes an hour or two.
What you are doing is allowing the gears to heat up and cool down. This tempers them and makes them incredibly hard.
10 cycles should be fine. Some say less, but to be safe, 10 cycles is fine.
"Do I need a bearing kit?"
Yes and no. It never hurts to replace the bearings, however you need to be sure you're getting the right ones. If your car has low miles, you can probably skip it. If your car has moderate-high miles, it's strongly recommended.
"What is this '3.73' '4.10' and all the other numbers about?"
That would be the ratio of teeth on the ring to the number of teeth on the pinion. Basically, when the engine completes a cycle, that rotation is translated to another in your transmission. Your transmission has gear ratios for every gear that's in it. The transmission output is transfered along the driveshaft and into the differential. Here, the rotation reaches the rear gears. Stock gears are typically 3.27 or 3.55. Basically, that means that for every 3.27 or 3.55 rotations provided by the transmission, your tires will spin once.
Now you can see why higher gear ratios allow you to accelerate faster. More power can get to the ground within the same revolution.
"Can I install gears myself."
Sure. Why not? You need the right tools to do so and unless you have someone there to help you, you might have a difficult time. I recommend allowing a professional to install them unless you are very familiar with how the differential works and are mechanically inclined.
"What does installation cost?"
This depends on where you go. Some places have work rates of 50$/hr. Some places have rates of 75$/hr.
Generally, installing gears takes 6-8 hours.
If you get a bearing kit, it will be slightly longer.
This depends greatly on how experienced the mechanic is and the condition of the existing bearings.
I paid 400$ to have mine installed with new bearings.
"4.10s are too much"
Too much for what? 4.10 is one of a few ideal ratios for a modular 4.6l engine.
"Ok, 4.10s are too much for a car using a power-adder"
No. 4.10s work excellent on both N/A cars and cars with forced induction. What determines whether the gears are "too much" is your ability to get the power to the ground. In which case, you should strongly consider getting stickier tires. If need be necessary, get drag tires.
There are DOT approved drag tires.
"Ok, what about 4.30s?"
Again, 4.30s will not be an issue if you have a means to get the power to the ground. Even people with 4.56s can run a power adder and get the power to the ground with the right tires.
"Wow, 4.56s? How would that work on an N/A car?"
Fine. You'll run high rpms on the highway but unless you have a lead foot your car will be just fine. It all depends on what you plan on doing.
"What do you recommend for gears?"
There is no "right gear ratio." Every ratio has an advantage and a disadvantage. You can keep your stock gears, throw on a power-adder and do just fine. Or, you can get 4.10s, accelerate like a bat out of hell, upgrade to some sort of power adder, and do just fine.
Overall, I and many others find that 4.10s are ideal.
"Why 4.10s? I know lots of people with 3.73s"
Again, you must choose between performance and drive-ability. People who choose 3.73s probably thought that 4.10s are too steep. That's fine. 3.73 will provide additional acceleration over the stock gears. Some people who purchase 3.73s have later swapped them out for 4.10s.
Some people with 4.10s have swapped them out for 4.30s.
"What kind of gain can I get with higher gear ratios."
The jump from 3.27s to 4.10s will get you 25% more rpms at any given speed.
This translates to greater acceleration regardless of rpm/gear and may result in a higher achievable rpm.
Performance gains (number-wise) are determined by what you have done to the car. Some people claim that you are trading horsepower for torque, but that is untrue. In reality, you are gaining both if you get the ideal ratio for your engine's output. *cough 4.10 cough*
"What if I have a Cobra."
Same thing, but since you have a 4V cam assembly, you have your choice of 4.10s and 4.30s for ideal ratios.
I hope this helped.
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96' GT 5-speed
BBK X-pipe w/high flow cats
BBK fenderwell CAI
Flowmasters
SCT SF3 Xcal w/93 oct tune
Which gears for highway? 1997 Mustang GT 
