rookie question

[jdubs]

i'm pretty new to the aftermarket scene, and i was wondering what exactly does changing the gear ratios do?
thanks

[Domestic Violence]

it moves the power. 4.10s = lots of power down low, crappy top end. 2.73s = no power down low and higher top end. with equal power, a car with 3.42s will be faster off the line, but the car with 3.23s will have a higher top speed.

that's why faster cars are going to 6 speed transmissions. they have an extra gear to lower the RPMs at higher speeds for fuel economy. the saleen S7 can max it's 6th gear at 223. if you were to change the gear ratio up or down, it would lower or raise that top speed and change the power band.

[satellite98]

At about what speed does the 3.42's (or even 3.73) start to "lose" top end-compared with the 3.08's?

[AlienInv8r]

Think of it sorta like riding a bike. Your transmission changing gears is like your rear derailler. The gear ratio is like your front chain rings, but you're stuck with just that one ratio.
~Let's say 3.08/2.73 are like the big chain ring. You take awhile to get moving from the start, but once you get going fast you can keep pulling a lot harder.
~3.42 are like the middle chain ring. You can start off decently fast, and pull pretty fast once you get going too. 3.42s are generally considered to be the best of both worlds since you get a good launch and still pull hard on the top end also. (from and A4 standpoint, M5's generally go for 3.73s)
~And 4.10s are like starting with your smallest chain ring. You can get up and go (ie-launch) really fast, but you run out of steam on the top end; your pedaling (engine rpms) is maxed out but the ratio doesnt let you go as fast at the same rpms.

That's how I came to understand what gears do, I hope that makes sense in how it was explained. You dont necessarily "lose" your top end with numerically higher gears. If we had no speed limiter, your top speed would be lower with the higher number gears. You will reach the top speed faster with numerically higher gears, but you do that at the expense of gas mileage and cruising rpms. A car with 3.08s will cruise the highway at lower rpms than a car with 4.10s at the same speed since the engine has to turn faster to maintain the same speed.

[jdubs]

now it makes sense, thanks for the response guys. how much would a 3.42 gear ratio cost and where could i get it done?

[AlienInv8r]

To buy the gears new they're about $200 and you can get em from any of the board sponsors. I got mine on eBay taken off an SS for like $20 though, so you can save some cash that way too. You'd probably want to add a Limited Slip Differential too when installing the gears, about $100, so that both tires will spin when you're launching. Right now you most likely have the open differential which gives power to the one tire with least traction. After a gear swap, you'll want all that new-found torque going to both tires rather than just one. And then you'd just need an install kit ($100) and an ABS reluctor ring if you wanna keep your ABS brakes ($20). So in parts you're lookin at roughly $420 new, or less if you find things used.
Most mechanics will do the install for like $200-300 on average. Call around and make sure the mechanic knows what he's doing since there's a few measurements that have to be pretty exact when installing the gears.
A lot of your questions can probably be answered with a search too, there have been tons of gear questions in the past and someone has probablyhad the same concerns as your before at some point.

[Ian]

It is probably easier for you to find a rear from a Z28. I know here in philly, there is a guy who has rears from 4th gen Z28's for $250. They already have 3.42's, LSD, and also have rear-disc breaks. They are a great deal at $250.