Want to know the Effect of Changing Gear Ratios? Look Here First!
Stock Gear Ratios:
M6: 3.42
A4 Standard: 2.73 (GU2 code on the door sticker)
A4 Performance Axel: 3.23 (GU5 code on the door sticker)
WS6 and SS models came with 3.23s.
Your A4 did not come with 3.42s.
If your sticker is gone you tell which gears you have by your highway rpms:
3.23s @ 2000 rpm = 67 mph; 2.73s @ 2000 rpm = 80 mph
3.15s were available in A4 Vettes
The attached file has the mph & rpm for the most popular gear ratios for F-bodies:
M6:
3.73
3.90 (requires aftermarket rear)
4.10
A4:
3.42
3.73
4.10
The mph assume a stock 245/50/16 F-body tire. Those on 17" wheels will find this pretty close since your tires are a narrower aspect ratio. If you run ET Streets, they are generally larger than stock tires. Depending upon which tire you select, you can add 2% - 5% to the mph numbers to estimate your rpm for a given trap speed.
A stock A4's converter is unlocked at WOT. Therefore when you cross the line your rpms will be higher than shown in the chart. While the amount slip will vary by converter, you should figure an extra 5 - 8% above the rpm shown in chart when looking at the high rpm numbers where you are likely to be at WOT.
If you want to play further with tire sizes and gear ratios go here:
Swapping from 3.23s to 3.42s is a waste of money. There is barely enough gain to justify the cost of a bottle of gear oil and additive, no less buying the gears. If you have 3.23s your next move is to 3.73s.
If you don't have a high stall torque converter, you really should look at that first. The big gains come from a converter, not from gears. You'll be amazed what a 3000 stall converter will do to the launch of a 2.73 geared car. Look in the automatic transmission forum for more info on them.
__________________ 2008 Atomic Orange C6 Z51 M6 - LG Pros w/ cats, Vararam, 160 T-Stat, HPT
Gone but not forgotten: 2002 SS vert
RIP: Z28 vert 11.58 @ 117.0 1.63 3800 lbs. 99 Mods and Pictures
Last edited by Ragtop 99; 11-30-2005 at 03:38 PM..
Higher gears will likely lower your mpg on the highway since your cruising revs will increase.
In town, as long as you shift more often, your mpg should not be effected. In other words if with 4.10s you use 5th gear whereas with 3.42s you would have used 4th gear, your mileage should be about the same... if your driving style is unchange.
__________________ 2008 Atomic Orange C6 Z51 M6 - LG Pros w/ cats, Vararam, 160 T-Stat, HPT
Gone but not forgotten: 2002 SS vert
RIP: Z28 vert 11.58 @ 117.0 1.63 3800 lbs. 99 Mods and Pictures
Stock Gear Ratios:
M6: 3.42
A4 Standard: 2.73 (GU2 code on the door sticker)
A4 Performance Axel: 3.23 (GU5 code on the door sticker)
WS6 and SS models came with 3.23s.
Your A4 did not come with 3.42s.
If your sticker is gone you tell which gears you have by your highway rpms:
3.23s @ 2000 rpm = 67 mph; 2.73s @ 2000 rpm = 80 mph
The attached file has the mph & rpm for the most popular gear ratios for F-bodies.:
M6:
3.73
3.90 (requires aftermarket rear)
4.10
A4:
3.42
3.73
4.10
The mph assume a stock 245/50/16 F-body tire. Those on 17" wheels will find this pretty close since your tires are a narrower aspect ratio. If you run ET Streets, they are generally larger than stock tires. Depending upon which tire you select, you can add 2% - 5% to the mph numbers to estimate your rpm for a given trap speed.
If you want to play further with tire sizes and gear ratios go here:
Swapping from 3.23s to 3.42s is a waste of money. There is barely enough gain to justify the cost of a bottle of gear oil and additive, no less buying the gears. If you have 3.23s your next move is to 3.73s.
If you don't have a high stall torque converter, you really should look at that first. The big gains come from a converter, not from gears. You'll be amazed what a 3000 stall converter will do to the launch of a 2.73 geared car. Look in the automatic transmission forum for more info on them.
All this info. pretty much applies to only F-bodies............Automatic Corvettes can come with 3:15 gears as well.
But do you have to have an aftermarket rear differential to go with 3:90 gears for the y-bodies? I don't think you do, but I'm not completely sure. I just had a built rear diff with 3:90 gears intalled in my Vette, but was wondering if I could have just put the gears in by them selves.....
__________________ -Jon-
2007 Blck/Blck Trailblazer 3SS. I'm not modding this one.
2007 Suzuki GSXR 750
2000 C5 Corvette Coupe, Blk/Blk with a few minor mods....Sold
I don't agree with the idea of getting a converter before gears. When you order your converter, it will be built based on the gear ratio you are running. Why get a converter built for 3.23's, then a few months later bump up to 3.73's? The two need to cork together, and the best way to do that is to have the gears you want to run in your car when you install the converter. JMHO...
Not sure about the details; but when I got my converter, they put in a 2.5 STR because of my 3.73's. If I had 3.23's I think they were going to put a 3.0 STR. You'd have to get with the tech rep when you get your converter built. That's all I know, but someone else might be able to shed some more light on the subject....
Marc:
For a typical F-Body street & strip use, gears will have only a small impact on converter selection. If you have higher number gears, people tend to be willing to live with a higher stall because it doesn't feel as tight. . Don't worry about the impact of gearing on effective stall speed...if you launch with good DRs/slicks you'll notice no change in stall speed with a swap from from 3.23s to 3.73s. Run a PG with a 1.6 first gear and you may notice a little difference, but the 4L60's 1st gear of 3.06 cuts it way down. The optimal stall on these cars (from stock to all but the most radical cams) is typically right around 4200 +/- 200, so if you running 4000 or less, gears will have no impact.
If you get a converter, the need for gears diminishes greatly. Once you have a 3000+ stall, switching from 3.23s to 3.73s yields .1 max and 1 mph. Given the problems that can develop with gear whine, it would not be high on the mod list.
I don't know what stall speed you were looking at or the details of your set-up, but a .5 change in STR is a lot. It was much harder for me to launch my 2800 3.0 STR than my 3500 2.5 STR. If you were considering a 3.0 STR on 3.23s, I can only assume you are planning to run good rubber.
Some people definitely like getting gears and don't like converters, but for most getting a converter does a better job from a performance standpoint.
00 Vette: I'll add the 3.15 for vettes. I thought that was optional as I have seen 2.73s in vettes. I have seen 3.90s in built differentials for vettes; I haven't been involved in a vette gear swap, but it seems a lot more expensive than an F-body...
__________________ 2008 Atomic Orange C6 Z51 M6 - LG Pros w/ cats, Vararam, 160 T-Stat, HPT
Gone but not forgotten: 2002 SS vert
RIP: Z28 vert 11.58 @ 117.0 1.63 3800 lbs. 99 Mods and Pictures
Last edited by Ragtop 99; 10-17-2005 at 11:21 PM..
So you're saying you could keep the 3.23's for highway gas mileage, yet still get similar performance of someone who is running 3.73's?
Absolutely. Gears feel like they make the car much faster, but back to back testing at the track shows the gains are pretty small (.1 and 1 mph) once you have a 3000 or higher stall converter. If you are a serious track hound, you'll want them to squeeze out all the performance, but there are plenty of 11 second cars running on 3.23s. 3.73s are nice for highway racing between 90 and 120 mph compared to 3.23s. On the street, 3.23s are better for stoplight racing. When I had a YPT 4000 and 3.23s, I could launch really hard on the street.
__________________ 2008 Atomic Orange C6 Z51 M6 - LG Pros w/ cats, Vararam, 160 T-Stat, HPT
Gone but not forgotten: 2002 SS vert
RIP: Z28 vert 11.58 @ 117.0 1.63 3800 lbs. 99 Mods and Pictures
Oh..... I feel like a dumbass. I've always been under the assumption that gears were a definite must first mod. Makes me kinda wish I would've talked to you before I did my setup. Oh well, better to learn late than never, right?
One thing to note with the attached file for A4s, those values are close to TCC locked numbers, not accurate for unlocked speeds. You will need a way of logging the Input vs. Output shaft speed to determine your loss percentage, then apply that value to the table and get more reliable values.
__________________ George P. Lara 2001 Camaro SS #0391: FQuick Garage
Stock Gear Ratios:
M6: 3.42
A4 Standard: 2.73 (GU2 code on the door sticker)
A4 Performance Axel: 3.23 (GU5 code on the door sticker)
WS6 and SS models came with 3.23s.
Your A4 did not come with 3.42s.
If your sticker is gone you tell which gears you have by your highway rpms:
3.23s @ 2000 rpm = 67 mph; 2.73s @ 2000 rpm = 80 mph
3.15s were available in A4 Vettes
Hmm I have a GU5 and at 2000rpm I am at about ~75-80mph...
Swapping from 3.23s to 3.42s is a waste of money. There is barely enough gain to justify the cost of a bottle of gear oil and additive, no less buying the gears. If you have 3.23s your next move is to 3.73s.
Good info, so what about the M6?
Is it a waste to go from 3.42 to 3.73 or should one just jump straight to 4.10's?
I went from 2.73's to 3.42's on my 95 Z28 and I picked up .3 second 1/4 mile time went from 14.2/98mph to 13.89/102mph and the car felt a whole lot better on the street. It woke the car up no more flat spots it was like having a different car.
Then I changed from 3.42's to 3.73's and the car didn't feel any better!
This was all on my 95 Z28 LT1 which I sold.
When I sold the car I put the 2.73's back in there and I have the 3.73's sitting here and I am thinking of putting them in my 99 Z28 Ls1 Camaro.
But I read something about the 99 cars having a paddle fixing instead of the pin to hold the c clips in?
Anyone have an info on this?
Cheers Andy
__________________ 99 Z28 Camaro A4 Now Sold
SLP headers 3" y pipe high flow cats TCI streetfighter TC.
Want to know the Effect of Changing Gear Ratios? Look Here First! 
thanks for the info I always like to learn something new
2:73 to 3:42 
