Mellow- Yellow

I have had my baby for almost one year now and have been wondering about the 3.15 gear ratio that I paid extra for when I bought the car. The car was bought from the dealer showroom and during negotations concerning price I failed to ask my salesman what advantages there are to having this. I have done a lot of searching and reading on the forum and have not really had my question about this answered. I am not mechanically inclined so I really do not know anything about gear ratios. Are there any advantages to having this and if so, what are they. Will this affect gas mileage. My car is automatic. Thanks for any info.

yell03

It is a great option to have for the A4 auto tranny.

My C6 Vert automatic with a 3.15 rear ran a 12.57@110.67 with a 1.92 60' time.

The 3.15 rear is lower geared than the stock 2.73 rear which provides better acceleration.

Howard

Mellow- Yellow

Thanks for the reply Howard. Any idea if it has any effect on gas mileage?

yell03

Not much if any effect on gas mileage.

My 2005 C6 automatic with the 3.15 gets over 16mpg in the city.

My 2006 C6 manual tranny barely gets over 13mpg in the city and sometimes less.

Howard

rick229

You will get less gas mileage with the 3:15's that the 2:73's. About 2-3 miles less.

catbert

On a trip I get 2 mpg less with the 3:15 C6 than my 2:73 C5.

yell03

I can't believe it is that big of a difference.

I don't care, but I am shocked.

Howard

cg205

But if you live in a hilly or mountainous area, you might make up for the lower highway mpg with better mpg in rural/city driving. I have the 3.15 in my A4 '05 vert, and in my mountainous area, I get 22-24mpg all the time. I have never gotten less than 22 in my 7200 miles I've had it. I use cruise even in mountainous areas, and with the lower rear gear and huge torque, it never shifts down when going uphill and the rpms will rarely vary much as it is doing it.

Mellow- Yellow

I haven't tried my car on the strip yet so I don't know what it will do but are you saying that a car with a 3.15 ratio would probably turn in a better time than one with the 2.73 ratio if everything else was the same?

Patman

A 3.15 geared car should get about 2-3 MPG less on the highway than a 2.73 geared car, but around town both will be about the same.

In the quarter mile a 2.73 geared car is probably about two tenths slower. It also won't feel as "snappy" off the line when driving around town as a 3.15 geared car does. I sure was happy when I checked the glovebox codes on my C5 and saw the G92 code for the 3.15s!

yell03

Yes, the 3.15 rear is going to be better at the strip than the 2.73.

Howard

LS WON

3:15's Better acceleration off the line but higher RPM's at freeway speeds. A little bit less gas mileage than 2.73's. I get about 22 MPG combined with 3:15's.
Does this mean your top end speed will be less with 3:15's vs. 2.73's?

sweetc6

I have a 2005 z51 a4 and I find down low these 315 gears to be very lazy . Im changing them to 342 and also putting a tci stall converter to give the car some life off the line.

Patman

You'll barely notice the change from 3.15s to 3.42s, you might as well go with 3.73s. I had a 95TA with 2.73s and changed it to 3.42s and it didn't make that much of a difference in SOTP feel. So going from 3.15s to 3.42s will be not much of a difference considering how much you'll spend on the swap. You might want to just do the converter swap first and then see how it feels, you might even want to stick with the 3.15s once you do the converter.

own2vettes

The better bang for the buck would be a converter. That alone will probably shave a couple of tenths off 1/4 mile times on an otherwise stock car.

catbert

Probably not. The Vette is more drag limited at the top end than gear limited. Top speed runs are not made in top gear because the motor won't support an overdrive transmission gearset...at least stock.

rulez

I am doing a 2.73 to 3.73 swap eary next month, and will keep the 2.73 just in case. I don't plan on installing a converter until I put a cam in it. At that point the converter might be required.

nuvetteowner

The a4 2:73 rear combo gets the best fuel economy of all the c6 models

rambo

I've heard this before and don't understand what it means. Please explain.

rambo

shockwaveharry

If my A6 with a 2.56 final drive could pull 6500 rpm's in top gear, I'd be going 296.07 mph!!! Since I don't have the kind of power needed to go 300 mph yet ( ) I have to settle for 186 mph at 5200 rpm's in 5th. Upshifting to 6th would drop the motor down to about 4200 rpm's where less power is available and the car would slow down.

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