ok, i hear so much about guys changing their gear ratios, to better acceleration. i was wondering how this is done and what some reccomendations on what to change it to, might be. i'm sorry, i can't tell you what i have now, but my car shifts around 4500 rpms (i think). thanks

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'91 Camaro RS, Fresh Paint Job, K&N Filter, Twin Turbo Hood, Soon to have Hooker Cat-back

 

YOUR CAR SHOULD HAVE 3.43:1 GEARS IF THE PREVIOUS OWNER DIDN'T CHANGE THEM. THOSE GEARS ARE USUALLY GOOD ENOUGH. IF YOU WANT YOUR CAR TO SHIFT HIGHER PUT IN A SHIFT KIT, PERFOMANCE SERVO, OR A HIGHER RATED GOVERNOR. YOR LOCAL TRANSMISSION SHOP SHOULD BE ABLE TO HELP YOU WITH THIS.

 

You have 3.42's if it's a standard, and 3.23's if it's an auto, but since you gave the RPM's it shifts at, then I'm assuming that you have an auto. You must not have your foot buried in the floor either if it's shifting that early.

The way you change them out is by changing the gears in your rear differential, which (unless you're professionally trained) you'll probably want to have someone do for you. You'll also have to calibrate your speedometer to give you an accurate reading.

2.73's will give you more top end, and gas mileage (my friend's 91 Z cruises around at 1200RPM), but you'll lose low end. 4.10's on the other hand will give you better 0-60 times, but you'll lose out on top end.

Hope I helped.

 

Hey thanks... you have no idea how much i've learned from this board. How much would it run me, would you guess, to have my gears changed out by a professional. i'd probably prefer the one that increases 0-60 times.

 

If you stay off the highway and under 110 look into some 4.10's so you can rip through the 1/4 and 0-60.. Run some 235 60R15's and your final ration with your tires will be like 4:00~3.90 I am told due to thte tire diameter...

 

Gears usually cost $200; installation costs $200. There's quite a few things (pinion preload, backlash, etc) that need to be checked & set for gears; set them wrong and you can destroy your gears with one drive!

The idea behind gears is to keep your engine in it's powerband. You've probably noticed that your engine performs really strong in a range of RPM's.. probably 2500-4500 (if I remember the 3.1). By changing the rear gears, you raise or lower your engine's RPM's at a certain speed.

For instance- Say you go to the racetrack, you have an automatic trans, and that your powerband is 2500-4500 RPM's. You notice that when you finish the 1/4 mile, you're running through the traps in 3rd gear, at 1200 RPM. That means your engine's not as powerful as it could be by the end of the racetrack. Ideally, you'd want your car to run through the traps, in 3rd, in it's powerband- say, 3000 RPM.

To do this, you'd install lower gears. Lower gears are numerically higher- as in, a 3.73 rear gear is "lower" than a 3.23 gear.

Like Brian said, you can change your car's "effective" rear gear by changing the rear tire size. If you want to lower your effective gear ratio, install a shorter tire. If you want to raise your effective, install a taller tire.

For instance: Last August, I swapped a 3.73/posi/disc axle into my car, from an '84 Trans Am. I have P275/60r15 tires on the car. Comparing the two ratios, one with my "original" tire size of P215/65r15, and the "new" size of P275/60r15, my effective rear gear ratio is a 3.46.

My original rear axle had a 3.42 gear in it. With the P275/60 tires, the effective was down to something like a 3.18. By changing my rear gear (actually, the whole axle), I lowered the effective to a 3.46- and I felt a seat-of-the-pants improvement.

For a good tire size & gear size calculator, check out this website: http://www.tolan-hoechst.com/cars/tirecalc.htm

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-Tom P (Hot rodded 1986 Firebird 2.8l)