I have a 91 firebird with an L03. I just have minor engine mods (exhaust, 82-84 style powerbuldge hood intake.) I just got done installing an energy poly bushing master kit along with new shocks (makes a HUGE difference btw) I'm planning a few more mild engine mods, maybe headers and high flow cat, underdrive pullys, nothing major. Anyway, I would like to put some gears in to help out the acceleration. I don't need anything to crazy, but something to give a little more kick. It's an automatic, this website says it has 2.73's in it now. I have drums in the back. What would you guys recommend for gears?

 

The 3.42 works very well with the 700R4 transmission.

 

I love my 3.42's. But mine is a 350 TPI.

 

What would be the difference between the way my L03 responds to the new gears and the way your 5.7 TPI responds. Would there be drawbacks to using the gears?

 

The only drawback will be kicking yourself for not doing gears sooner. You will LOVE LOVE LOVE the 3.42s. Your speedo will be off, but that can be fixxed as well.

Your mpg should stay the same after you get over mashing the gas to feel the difference in acceleration.

 

On L98's and LT1's I've had 2.73, 3.27, 3.45, and 3.73

2.73 = fun on the highway (70-100 mph cruising). Not so good for acceleration. A big converter and 2.73's can be fun. That way you get the speed of the converter and the gas mileage and cruising of the 2.73's. At the drags, you can still get traction while springing off the line with the converter. 1st gear is usable in that regard.

3.27 = a good all around ratio. Doesn't rev too high. Not too tall either. Cars wants to do the 3-4-3-4 shift around 40 mph.

3.45 = a bit more zing than 3.27. Still good on the highway. Car wants to shift 3-4-3-4 at 30 mph.

3.73 = too much gear for an automatic. With our 3.06 first gear, it's too much. Driving on the highway in O/D is like driving on the highway with 2.73's in 3rd gear.

If you have 2.73's, I'd recommend the 3.27 or 3.45 (3.45 being preferred).
If you have 3.27's, I wouldn't bother going to 3.45 or 3.73. Keep what you have.

3.73's are really for 6 speeds. With their 2.66 1st gear, that's the same as an automatic with 3.27's in 1st gear. But the 6 speed/3.73's can still have a deeper overdrive for low RPM highway cruising (and actually make 6th gear usable). 4.10's are even more fun.

 

Fixed for you.

**Edit fixed for me. I wasn't operating on all 8 when I wrote that.

 

Never had an LB9....But I'm guessing the 3.45 gear for them would be the most fun and best overall.

 

I switched to 3.42 from 2.73 gears, and I got according to a chart, a 25% increase in torque. I really feel the difference with my carbed 305. It made all the difference in the world. yes.. the 273's are great for the highway, but i perform much better w/ the taller 342's. You will nottttt regret it. I wanna get the same gears for my 92 rs w/tbi 305.

 

The torque curve seemed much flatter than before the switch also since I am getting the revs sooner with each shift.

 

3.42's good gear - decent mileage, nice seat-of-the-pants feel. I really like mine.

 

Well that sounds good for me to upgrade. Just have to remember to get the speedometer gear that will go with it.

 

Personally, I prefer 3.73 gears for an auto.
I had 3.23 and went to 3.73 and it was a night and day difference.
At the drag strip it knocked off 1/2 second and gave me 3mph on my otherwise stock 305.

When I converted to manual I still had the 3.73 rear end but it was whining really bad. buddy was trading in his 98 Firebird with a built 4.10 10 bolt so I bought the rear and put my 3.73 rear in his car.
4.10's is way too much gear for a T5 with a motor that runs out of steam at 5K rpm, 1st gear is waaaay to short, cruising at 2500-3K at 65mph in 5th and a top speed of 120something. mpg went down the toilet.
I tore that rear up and went to a 3.42 rear.

 

Sorry I didn't get back to you sooner. I switched to 3.42 in my 86 iroc, but I have the stock 2.73 gears in my 92 rs. I felt a world of difference in the iroc, but I thought of going to 3.23 gears in my rs so I could have a little more low end torque, but still have some highway gear left. Is there a torque increase, or is it better use of available torque?

 

it is a better use of the available torque. it might open up a few hp/tq that were previously lost due to friction

 

http://www.angelfire.com/fl/procrastination/rear.html

that a cool final drive ratio calculator that'll help.

and here's how to calculate your dire diameter:

http://www.cc.k12.nf.ca/sketch/tire2.htm

 

It sure made a world of difference in the iroc.