A6 3.91 gears or 1LE differential
 

Alright guys I kinda want this thread to be helpful for us A6 guys who are looking into the new gears 3.91 gears that chevy is now gonna start warranting. From my findings on this forum I have learned the following information which is helping me decided what are my options on this category.

1. A lot of M6 guys here have stated that the 3.91 gears are too much gear for our cars due to our differential being more aggressive than their M6. I don't think anybody that actually has a A6 that has the 3.91 gears in their car stated that it is too much for there car but you will have to be easy on the gas because it can be wild but it still is totally do able.

2. Because I know people will still say it is too much gear for our car can't us A6 guys just switch our super aggressive differential to a 1LE differential there for we don't have an aggressive 1st and 2nd gear? The only problem I see with is that I don't know if chevy will still keep our warranty with that part because it is more than just the 1LE gears.

3. If a A6 guy were to go and just get the 3.91 gears then some supporting mods that would help make these gears more practical would include some sticker tires and wider rims. Nitto Invo would be good for a set of street tires I would believe. My current set up is TsW Nurbergrings 20x9 front/20x10 rear. Invo Tires 275/40front 315/35. If anybody would like to include some suspension mods that would help with grip that would be great! The only thing I think that would help for sure would be some solid subframe bushings.

So list your opinion on this matter so we can have a solid amount of information for people who are thinking about doing this mod when this modification because fully available to everyone!
(Apparently if anybody leaves in Florida you can change your gears under warranty at the Chevy location in Fort Lauderdale next to sunrise if anyone was interested to do it now)

interested in this. as i am also torn between the 3.91 and the 3.73

The difference between the A6 and M6 is that the automatic transmission is geared more aggressively. That means it takes less gear in the rear to achieve the same result overall. 3.91 in an A6 car is compatible to 4.11 in the M6 but with even higher cruising RPMs. 3.73 in the A6 produces similar results to 3.91 in a M6 car. With supporting mods and tires you can do 3.91 in the A6 car, you just have to be careful. Especially in the wet.

Alright I get that now chase but my problem still remains I want my chevy warranty still intact as much as possible and they don't have 3.73 gears so the only choice I got is 3.91 gears.

1. The aggressiveness of the 3.91 gears in the A6 has nothing to do with the "differential" being different, it is because the 1st and 2nd gears in the automatic transmission are more aggressive than on the SS M6 transmission. If I remember correctly, the gears in the 1LE M6 transmission are even less aggressive than the regular SS M6 transmission.

2. The differential in a 1LE is the same as the differential in a A6 or M6 SS, just with 3.91 gears. As previously stated, it's the "aggressive gearing" in the transmission, coupled with the "lower" 3.91 gears, that makes some people say that the overall combination is too aggressive. I can't speak from personal A6 experience, but in reality, unless you're worried about getting the lowest possible ET's at the track, the 3.91's would probably be perfectly fine in an A6 street car. It's when you start getting into the high HP numbers and/or serious drag racing that the aggressiveness of the 3.91's becomes a problem.

3. Overly-sticky tires are only going to compound the aggressiveness, and you could start breaking driveline parts, such as axles, spider gears, etc.

Alright all good info so what would you guess would be the max amount of HP/TQ that someone should go up too with having the 3.91 gears before switching to 3.73 gears.

I have an A6 SS w/ 3.91 gears. Making 477 rwhp, 427 ft-lbs torque on Dynajet. I have about 75 passes on the gears and haven't broken anything yet. I have worn out a set of MT ET Street Drag Radials though. 1st and 2nd gear don't last very long, but I think if you had more HP and torque you could launch in 2nd gear and do just fine. 2nd is 2.36 ratio, whereas 1st on a 4L80E is 2.48. My car is set up to do this in M mode, but I'm a little short on HP and torque, so my 60' is not quite as good as with 1st gear.

Jeff

What does your car run at the track with that much power tho? 60ft? MPH?

PB so far 11.500 @119.90 mph, 1.69 60' with a converter that seemed to be only stalling to about 2600 rpm. Converter has been replaced, but haven't had good weather yet, hopefully tomorrow.

You got a slip? Not bad. What size tire?
Thinking about 3.91s but most can't 60ft my 3.27 gear 1.61 60ft. scared I won't hook.

Yes, I have a slip somewhere in my drawer. If you are suggesting I post it, I have no idea how to and not interested in being on the "fast list". Tire was MT 305/45 R18. Car dead hooked, but converter didn't flash high enough and tune pulled a lot of timing at launch. We're working on that, as car should be capable of 1.5x 60'.

Getting off topic and hijacked the OPs thread, didn't we? Sorry OP.

Edit: Went to Valdosta today (1/4/14) and ran 11.362 @ 121.09 MPH with a 1.63 sixty foot. DA was minus 524 Ft.

It's alright but now back on topic!

Gears really make a car more fun. My Corvette is manual with 3.90 gears. It really balanced out my 450ish RWHP. Without the gears, the car was fast. With the gears, the car was quick and fast.
Traction doesnt happen till 3rd gear on a 3200 pound car.

I calibrated a lot of Gen5 Camaros with 6L80 transmissions and 3.91 gears. With just bolt ons, guys are blowing through 1st and 2nd, and chirping 3rd. Sounds fun, and is fun, but at any decent power level, the 3.91s in the 6L80 transmission dont hook up well.

So I guess my point is if you are going to gear that high in an automatic, be mindful of your power level goals.

Phil

Reason I asked because of the MPH, just saw your 11.36 pass. Only wondering what everyone else run with the 3.91 gears. great pass none the less just MPH is a little low IMO. But that explains the pulled timing.