GT 3.55 vs 3.15 & Fuel Economy

[six_shooter]

So I've gotten a promotion at work and plan on upgrading to a GT soon. I was originally thinking procharging my V6 but honestly I just want the 5.0 sound and N/A power. Anyway I basically plan on getting the same car but with a 5.0 and some extra goodies. DIB, auto, spoiler delete and reverse sensors. My question is what is the difference in fuel economy and acceleration between the 3.15s and 3.55s with an auto?

I tried searching but couldn't find any different MPG numbers. I wouldn't care about a MPG or two but if its like 5 MPG I would go with the 3.15s.

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[1320']

As an aside...

One key thing to consider is that the 3.15's have a unique differential. If you're ever wanting to swap gears, I'd get the 3.55's since that will let you run the 3.31's, 3.55's, 3.73's or the new 4.09's etc.

3.55 is a bit of a short gear with the A6's...if it were me..I'd get the 3.55 and buy a set of 3.31's and swap those in...best of both worlds!

 

[six_shooter]

OK very interesting, I did not know that. I think I'll go with the 3.55s in case I decide to swap gears in the future. Are 3.31s even a factory option? I don't see that in the build tool.

 

[mjhousto]

I have an auto with 3.55. My average fuel economy over 13k miles is 22.5 mpg with a 50/50 split of city/highway driving.

 

[1320']

OK very interesting, I did not know that. I think I'll go with the 3.55s in case I decide to swap gears in the future. Are 3.31s even a factory option? I don't see that in the build tool.

Not for the automatic, they are the standard gears on the M6 cars without the PP.

You can buy the ring and pinion from your Ford parts counter or wait until Ford Racing releases them..which they will.

Multiple shops did testing on the 2011-2014 A6 Coyotes and found that the gains were essentially wiped out past 3.31's in automatics due to the aggressive gearing that the 6R80 has internally. Since the transmission gearing hasn't changed, and the Coyote hasn't dramatically changed...the results are still valid. If anything they're more valid since the S550's have a bit more weight to get moving.

A lot of people still are in the old C4/AOD mindset of needing 4.10's to get an auto moving..but even with 3.15's it's the same effect as having 3.90's in the rear end of a AOD/ 4R70W car...3.31's are equal to about 4.10's.

 

[BBB]

So much wrong with this post

1. Job promotion - lets get a V8
2. Get a v8, hey which one gets better MPG?

Are you sure you should even be buying a new car?

 

[1320']

So much wrong with this post

1. Job promotion - lets get a V8
2. Get a v8, hey which one gets better MPG?

Are you sure you should even be buying a new car?

It's not unreasonable to consider fuel economy with the 5.0

The old "if you're concerned about fuel economy you shouldn't get a V8" and "If you have to consider fuel economy, you can't afford XYZ" is so utterly black and white, "if and then" that it's not even funny.

It's a stupid argument. Some people want some balance and moderation in their choices..and it's unique to each person.

 

[15COPP]

3.55

 

[Tcstang]

I have the auto with 3.55's. I have 8500 miles on my car and the lifetime average is 16.9 mpg. I do 95% city driving.

 

[Chad11491]

It's not unreasonable to consider fuel economy with the 5.0

The old "if you're concerned about fuel economy you shouldn't get a V8" and "If you have to consider fuel economy, you can't afford XYZ" is so utterly black and white, "if and then" that it's not even funny.

It's a stupid argument. Some people want some balance and moderation in their choices..and it's unique to each person.

He makes a good point though. If you weren't able to afford a gt comfortably before, most promotions aren't more than 5-10k a year extra. If a v6/ecoboost put you at your comfort limit, a gt might be stressing your income even with a promotion due to the extra insurance, gas, and consumables cost. It might not be the smartest choice. Things can happen, and you don't want to stress your income to the hilt in case they do by adding on all the extra costs of a new car. Not saying that's the OP's position at all, just saying he made a valid point.

 

[BBB]

He makes a good point though. If you weren't able to afford a gt comfortably before, most promotions aren't more than 5-10k a year extra. If a v6/ecoboost put you at your comfort limit, a gt might be stressing your income even with a promotion due to the extra insurance, gas, and consumables cost. It might not be the smartest choice. Things can happen, and you don't want to stress your income to the hilt in case they do by adding on all the extra costs of a new car. Not saying that's the OP's position at all, just saying he made a valid point.

Bingo. If it's coming down to the gear ratio and how much gas one uses vs another, you probably shouldn't and can't afford to buy a new car.

You're going to eat it on depreciation
You'll eat it with insurance
You'll eat it with gas

 

[jasonstang]

Good fuel economy: 3.15
Good acceleration: 3.55

 

[paul123]

One key thing to consider is that the 3.15's have a unique differential. If you're ever wanting to swap gears, I'd get the 3.55's since that will let you run the 3.31's, 3.55's, 3.73's or the new 4.09's etc.

3.55 is a bit of a short gear with the A6's...if it were me..I'd get the 3.55 and buy a set of 3.31's and swap those in...best of both worlds!

why do the 3.15's have a unique differential?

I probably wouldn't buy 3.55 with plans to mod it with 3.31. Swapping the gears is intrusive and there should be a good reason to do that.

 

[1320']

why do the 3.15's have a unique differential?

I probably wouldn't buy 3.55 with plans to mod it with 3.31. Swapping the gears is intrusive and there should be a good reason to do that.

I'm not sure why they have a unique differential, all I know is they do.


All I know is that if you buy a 3.15 car, and do want to change gears, it's going to be a much more expensive prospect. If you're entertaining changing gears at any point in the future, 3.55's is the best starting point on automatics.

 

[DR_]

The Traction-Lok M-4204-M differential used with the 3.31 and up is only $175 new and people pretty much give them away free if used. The carrier is the same, just the diff needs to be also changed out.

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