GT automatic stock 3.15 or 3.55

[jcovaltine]

I have been reading through the different threads on this topic but only seen one member post actual mpg with 3.55 on automatic. His results are impressive but I wanted to know what others have to say about the different options for a GT automatic. After work I'm heading to my local dealership to special order my vehicle. I have decided on the following

GT Premium
400a
Automatic
Enhanced security package
19" premium painted wheels
Navigation
Rear backup sensors
Premier leather trim

3.15 (stock) or 3.55 rear end????:headbonk::headbonk: I can't decide. This is going to be a daily driver. To and from work. 50/50 city, highway

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[sandbagger]

I would go with the 3.55 myself I had 4.10 in my wifes 07gt and loved them had 4.30's in my 2011 GT

 

[Jsboening]

I'd go 3.55 just for the additional kick in the pants feel. I'm guessing you might loss 1mpg if that.

 

[Wolfman625]

3:55!

 

[jcovaltine]

1 mpg isn't bad. Someone mentioned the 3.55 gave them better around town mpg.

 

[1320']

1 mpg isn't bad. Someone mentioned the 3.55 gave them better around town mpg.

Yes, there is a trade off.

What will remain to be seen is if 3.55 or 3.15 cars produce better dragstrip times.

There is a chance, I am unsure as to how much, that 3.55 gears may cause an extra shift during the run, thus you might actually produce a worse ET than a 3.15 car

 

[K-Loader]

My initial order was the 3.15 gears, but a week ago had second thoughts and I modified my order to the 3.55 rear end. I have a 60 mile round trip to work. It’s a 40 min, almost non-stop trip in the morning, and 70 min stop and go, heavy traffic ride home. I figure the round trip mileage would be a wash, with the 3.11 doing better on the non-stop ride in, with the 3.55 doing better on the way home. The 3.55 wins because I’m convinced it will be more fun on the weekends.

 

[STAMPEDE]

THREE:FIFTY FIVE

 

[jcovaltine]

My initial order was the 3.15 gears, but a week ago had second thoughts and I modified my order to the 3.55 rear end. I have a 60 mile round trip to work. It’s a 40 min, almost non-stop trip in the morning, and 70 min stop and go, heavy traffic ride home. I figure the round trip mileage would be a wash, with the 3.11 doing better on the non-stop ride in, with the 3.55 doing better on the way home. The 3.55 wins because I’m convinced it will be more fun on the weekends.[/QUOTE

I had a 2002 Mustang GT I put 3.73 on and it was a lot of fun around town but it was horrible on the freeway. I feel that 3.55 wont be that much of a difference. My concern is what the RPM difference will be while driving 70 mph on the freeway. I'm leaning towards the 3.55 right now.

 

[jcovaltine]

THREE:FIFTY FIVE

What did you order with yours?

 

[K-Loader]

Below is some data put together from some testing of a small block Nova some 20 years ago with various rear end gear ratios. It was printed in the June 95 issue of Hot Rod. It helped me put in perspective the performance difference I may see between the 3.15:1 and the 3.55:1 gear ratios.

 

[Five Oh Brian]

Save the money for the 3.55 upgrade from the factory and install 4.10's after you take delivery. You're going to get a tuner for more power anyway (right, everybody!?!?), so you can use the tuner to correct your speedo. Or, invest in a big stall converter (Circle-D makes awesome stall converters for the 6R80 trans). Better yet, get the 4.10's and a big stall converter.

 

[Jimdohc]

...what the RPM difference will be while driving 70 mph on the freeway...

70mph:
3.15 ~1,800rpm
3.55 ~2,030rpm

In my humble opinion,
street use:
street tires & NA- 3.55
street tires & Supercharger- 3.15

 

[STAMPEDE]

What did you order with yours?

3:55 all the way

 

[jcovaltine]

70mph:
3.15 ~1,800rpm
3.55 ~2,030rpm

In my humble opinion,
street use:
street tires & NA- 3.55
street tires & Supercharger- 3.15

Thank you for the detailed response. 230 rpm shouldnt be that much of a differences on mpg. Looks like 3.55 rear end is the way to go.

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