Warrio17

3.73 hands down! You will have trouble wiping the smile off your face. I am getting 17mpg city and 23 on Highway

Mulepick

Try running around in sport mode. To me this feels as tall as 3.73 if not taller.

learning

I have 3.55 in my auto and seems great. High teens low 20s in gas milage with CAI and 91 tune.

scottmach

You have a manual, he has an auto. Not an apples to apple comparison seeing as he has a steeper 1st gear.

Paul S. Safford

I have the same dilemma / question... Unfortunately or perhaps fortunately, I'm already committed. The car is resting on a lift at Murillo Motorsports here in San Antonio awaiting new bearings as the bearings on the stock piñon were too difficult to remove without damage. We are installing the 3.73s for my '13 GT/Auto vs. the stock 3.15s. Because it's an auto the dealer warned against driving it without updating the programming. In the '12s and earlier the update to the programming was simple, however, on the '13s, the dealer here in NW San Antonio informs me they can no longer gain access to the programming for gear ratio. Luckily I found Murillo MS, they specialize and race mustangs. They have a SCT tuner which will adjust the spedo, gear ratio, and apply some pre-programmed tune-ups. The gear swap is $640 out the door, and the tuner installed with labor is $411. I'll try to remember to post back with the results when I get her back, possibly Monday...

OGarza5.0

Murillo MS is awesome runs some of the fastest mustangs in Texas. I heard he's tuning is also great, i know people who take their mustangs to SA just for the tune.

Paul S. Safford

Thanks for the confirmation on choosing them. Initial impression is great - they took the time to explain everything to me and when they saw my honorable discharge license plate they volunteered a discount.

I picked up the car this morning and the difference is noticible. With the 3.73s & SCT tuner there is still enough traction, atleast with the 275 40/19 Micheline pilot super sports I have. But it will do just a little more then chirp the tires when the auto hits second. Highway, at 70 MPH, I went from about 2000~ RPMs to about 2,400~, 80MPH is about 2,750~, and 60MPH, who's gonna go 60? 60 was about 2,000 RPMs. I tried to pay close attention to the fuel consumption, I did only 25 miles on the highway and observed the onboard fuel consumption indicator, no significant difference. So my initial perception is there's less then a 5% drop in fuel economy if even that.

scottmach

That's odd because when I was on street tires with my 3.15's my car would just roast the tires.

VistaBlueFrank68

He might have his traction control on, try pressing and holding the T/C button and TC and Advance track will turn-off. Then roast em but be carful less you rap it around a tree.
Even in an auto with 3.73 your milage will go-up. 4.10 is where you really start to notice.
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Paul S. Safford

@Scottmach & VistaBlueFrank68, yes, I have the traction control on, just spent $800 on two tires and don't want to really smoke them just yet. The 3.15s with an Auto will smoke the tires if that's what you set out to do but you have to be on the right surface, either turning, up a hill, or pre-load. I had a '12 GT with stick and 3.31s, that would smoke 'em at the drop of a hat just by letting the clutch out a little fast.

I had to go back to Murillo Motorsport's again today because I forgot my stock gears at their shop. It's a 26 mile drive but it was 86 degrees and sunny - I dropped the top and cruised. Those guys are great, if anyone wants to do a mod and can get to them I totally recomend them. Here's why, in a nutshell they anticipate your needs or requests... I had changed the stock tires out before finding Murillo's, with the gear upgrade they installed a SCT tuner (model 3015). I was reading about the tuner last night and learned it can reprogram the computer/spedo for non-OEM tire sizes. So when I went up today to pick up my stock gears I asked and they had already programmed the correct tire size! I also wanted the 93 octane tune - again, they anticipated the logical tune. It's so different from doing anything at the dealer where you have to spoon feed them what you want done.