McGinnis

I currently have a stock 1999 Firebird Formula ls1 auto with 2.73 gears it does 2000 RPM at 80mph so I know thats the ratio I got. I want a little more power without sacrificing to much fuel economy. I know Trans Ams came from the factory with 3.23 gears, I am also considering 3.42, but don't wanna kill my fuel economy. I know that with my car currently it will max out in the high around 158 mph or so in 3rd gear it doesn't really have any pull in 4th gear, if I go with lower gears(higher numerically) will it max out in 4th gear or will it not be in the power band and cause the top speed to be lower? All the youtube videos seem to be with manual ones with a bunch of mods not 4l60e auto's. Also with gears I know the speedo has to be reprogrammed and the shift pointed re-flashed or something. My concern is I have a series 2 carrier in the rear end and i Know anything taller then 3.08 requires a series 3. I have seen some gear kits online that specify a series 2 even with gears with a larger number then 3.08, I'm assuming that they just us a thicker ring gear to compensate for the smaller pinion with a series 2. I have also seen series 3 gears and a spacer available as an add on to make it work. What would you recommend as far as getting gears set up and not whining, and anyone have a ballpark figure on what a reputable shop would charge to install and reprogram shift points and speedo error too?

ejbta2

My friend had a formula firebird with 2.73 gear and ran the same times as me with 3.73's because the tranny only used 2 gears thru the quarter he was shifting to 3rd going thru the traps we both had Yank ss4000 stalls. get a converter and keep the gas mileage or any good rear end shop can swap you some gears, in Tulsa they swapped for $500 parts and labor.

BODUKE

3.42 gears is a good combination for a a4.

farmington

iTrader: (14)

I got my 2.73's swapped for 3.73's. Heard that if you used the "thick" gears you had more probability to get whine, so I went with a new TruTrack posi unit. I used AAM gears. No issues 5 years later. You can change rear gear settings with a hand held programmer if you don't want to use a tuner shop. Might save you a little money.

RPM WS6

iTrader: (3)

Gear ratio changes do not effect any change in engine power, only mechanical advantage.

No, not all of them. 2.73 was standard for all A4/4L60E LS1 F-bodies, other than WS6/SS/Firehawk which required a mandatory 3.23 (GU5) option when ordered with 4L60E (MX0/M30). For non-WS6/SS/Firehawk models, 3.23 was optional on any trim level (Z28/Formula/Trans Am) with an A4/LS1.

Overall, I would look at a stall speed change before ever touching the gears on an 4L60E/LS1 setup. Gear swaps are much more important for M6 models, but with an A4 any ratio between 2.73 to 3.73 offers very little acceleration difference when matched to an optimized stall speed (3500+ for LS1s.) The higher numeric ratios will give a "tighter" feel to the higher stall speed, which some people prefer, but actual ET performance will be nearly the same (all else being equal, and with a 3500+ stall speed already in place, no more than about a ~0.15 second advantage for a 3.73 over a 2.73 and even less for ratios numerically lower than 3.73 - however, gear swap gains are much greater when stock or more mild stall speeds are still in place.) This post is a good example of how optimized stall speed mostly negates the acceleration advantages of higher numeric gear ratios:

01ssreda4

iTrader: (96)

GM75373x is what you want. Search that part number.

hardtrailz

So if not changing stall, is it worth it to go 3.23 over stock 2.73? What kind of gains are you referencing?

DANOZ28

iTrader: (1)

as for gas milage , i lost 2 mpg adding my stall. some articles said i wouldn't lose anything. a stall will really wake up your cars performance. if you have no plans to add a stall then maybe 3:42 gears wouldn't be bad. i've been looking at motive gears for a series 2 carrier part# G875342X. (i called motive)

RPM WS6

iTrader: (3)

The difference between these two is not really worth the cost of the swap, unless you have a complete 3.23 axle that you're just going to swap over. But then you still need a retune for the speedometer and shift points. If you're just going to do a gear swap and leave the stock torque converter, you'd want to move up to 3.73 to really see some improvement. That should give you a few tenths of ET reduction over the 2.73s with a stock stall speed.

But I would still HIGHLY recommend a stall upgrade. The improvement of a ~3500 stall speed, even with stock gears, would be about twice as big as just doing a 2.73-3.73 swap alone.

As far as a higher stall and MPG, there will be no change in MPG once in lock-up range (and this can be tuned to happen at a lower speed, if you so choose.) Any loss would only be at lower city speeds. With the gear swap, you'll get slightly lower MPG both city and highway due to higher cruising rpms at any steady speed.

Bob@BruteSpeed

iTrader: (16)

I would say it is not worth the expense, you wouldn't notice much of a difference for what you would be paying to swap the gears. If you went from 2.73 to 3.73 then yes, I'd say it would be worth it. Bob

hardtrailz

Great info. 3.73 will need a carrier swap as well, correct?

Bob@BruteSpeed

iTrader: (16)

All you have to do is to go to a thicker gear, here is a link to one that I sell.
http://shop.brutespeed.com/Moser-10B...-10B75373X.htm

Thanks. Bob

01WS6BLACKLS1

I have an 01 ws6 a4 bolt ons and 3.73 gears and tune. I too was on the fence stall vs gears. my choice was gears. reason being i drive the car daily spring through fall. literally 8 miles round trip to work and home no track time closest track is over an hour drive. so no track time for mine and I put maybe 2000 miles a year on. now for someone doing track time a lot I would say stall. I still am contemplating down the road a stall maybe though. the gears were in my opinion worth every penny man. 3.23 to 3.73 for me was definitely worth it. but I don't really race it either. street car good choice. if your going to do gears do it right. good set of gears stud kit for carrier bearing caps. solid pinion spacer. my preference anyway. and a girdle. my 2 cents. I'm am by no means saying no to the stall. but you have to look at how your driving the car too. and if you go stall get a good one with a good trans cooler.

RPM WS6

iTrader: (3)

I would still pick the stall over the gears, especially for a 3.23 car, even if it never saw the track. Do them both if you have the cash and/or ability, or do just the stall, but I'd never recommend just the gears. Too much is left on the table with the stock stall speed to justify the cost of a gear swap when the stock stall is still in place IMO.

If you think the 3.23 to 3.73 gain was worth it, you would be pretty surprised by the improvement from stock to a 3500-4000rpm stall speed even with stock gears. And it would be perfectly daily driveable with 3.23s and a top shelf converter.

Bottom line....higher stall is not just a track modification. For anyone looking for dramatic improvement in the performance of their A4 LS1, a higher stall is a must even if the car never leaves public roadways.

Bob@BruteSpeed

iTrader: (16)

I agree! Bob

01ssreda4

iTrader: (96)

Stall will gain more performance, no question. But I liked the seat of the pants of a gear change, your car may not be a whole lot faster but it feels like it, accelerates easier at light throttle etc.

FirstYrLS1Z

iTrader: (4)

^^^ this agree.

I'm a fan of both stall & gear change.

For 1/4 & 1/8 racing
Gains from a stall can be huge,gains from a gear change,typically,are small.

For everyday non-racing driving
You don't feel the stall until you open throttle position to awaken the beast,gear change is always felt.

Torque increase to pavement with gear change
2.73 to 3.23 = 18%
2.73 to 3.42 = 25%
2.73 to 3.73 = 37%

3.23 to 3.42 = 6%
3.23 to 3.73 = 16%

RPM WS6

iTrader: (3)

Gear swap is fine to wring out every last drop of performance or to change street manners if so desired, but IMO it's a waste if that blows the budget for a stall swap that hasn't yet been done.

In my experience, ~3500 stall speed will do more to increase the "street fun factor" than small gear ratio changes of 2.73-3.23 or 3.23-3.73. However, the impact would be greater from a change such as 2.73-3.73 or 3.23-4.10.

SteenH

Absolutely, stall plays a gigantic role.

hardtrailz

So 2.73 and stock stall---

It sounds like my plans should be for a 3.73 and 3500ish stall to maximize while retaining the drivability and commuting friendliness the car has.

Christmas is coming...