Leaning hard toward swapping my 3:15’s for 3:73’s.

Anyone doenthis swap and regretted it? Thoughts?

2016 GT stick.

 

If you care about gas mileage and spend a lot of time on the highway, you will regret it. Otherwise, you will love it. We're talking about 2+mpg less most likely.

 

 

I agree with "proeagles". I swapped to 4.10s and HWY sucks, city not too bad. Quick as Hell take offs but you take a big hit on MPGs.

 

I haven't swapped but I've owned and driven both. The difference is readily apparent. Plus a friend of mine had a F150 Ecoboost with 3.15 and mine had 3.73 and we had a little drag race and my truck left him in the dust. He gets about 21 mpg on the highway and mine only gets 19. I've also left Chevy and Dodge Hemi's in the dust.

 

I had OEM 3.73's on my former '08 Bullitt and loved them because they move the powerband down low- lots better bottom end and quicker acceleration. My '14 GT Track Pack also came w/3.73's and loved them on that car for the same reason.

I just had the OEM 3.31's on my '09 GT500 swapped to a set of FRPP 3.73's and am very happy I did the swap. Even as strong as the GT500 engine is, I felt the bottom end was soft. The 'experts' cautioned me against this, citing that the KR model of the GT500 had 3.73's because of the larger wheel size to which I said, 'bunk.' I was also warned about the MPG issue, which I chuckled at. The increase in bottom end power & roll-on was immediate & significant & my MPG has actually gone up.

The theory goes that your gas mileage will be grossly affected by 3.73's too. Well, my Bullitt averaged 24-27 highway MPG, my '14 GT T/P was well over 22 highway MPG and I've actually noticed an INCREASE in highway MPG since the 3.73 gears were installed on the GT500. I'm guessing the engine is now sitting in the 'sweet spot,' especially during my daily commute, where the engine is running at near optimal performance. I've seen 25+ MPG on some occasions but generally, the MPG has been up 2-3 MPG on the highway. I use to have to fill up every 2-3 days & now I'm getting at 4-5 days out of every tank.

3.73's are a win-win to me.

I will caution you, however, to NOT buy used 3.73's. Sadly, that was a lesson I learned that cost me time & $$. The gears looked perfect, brandy new even yet once installed, they could not be properly aligned and the dreaded whine was ever-present. I'd never buy used gears again, don't care how pretty they look.

Spend the extra $$ and get new FRPP gears, as well as the proper type/amount of oil and ring/pinion installation kit. Lastly, and perhaps most importantly, make sure the shop you bring it to knows what it's doing. Nothing worse than listening to whining gears that were installed improperly.

Good luck.
Lee

 

What "spectreman" said. Ford Racing gears on the only ones to buy.

 

Go find a 2017 GT with the 3.73's at a dealership and take it for a test drive. I know for a fact that two 2015 mustangs with 3.15 and 3.55 ratios will feel significantly different accelerating from a stop.

 

I did a 3:31 - 3:73 swap. I could not really tell that much of a difference but of course I never have really tried the car out prior. Until I get some good tires, trying to do anything out of the whole is pointless. But as far as mpg, 13 city, 24-27 hwy....Of course my riding around consist of playing around and I Haven't driven it that much to give you true numbers

 

Test drove 2017 GT 3.31, 3.55 and 3.73

3.31 is good for MPG and highway.
3.55 comes in the California edition and all 2018's here on out, It's perfect with the new 10 spd Auto.
3.73 PP on the 2017. Great all around especially off the line and in corners. (2nd gear is a dream, very easy to kick the rear out and lots of control)
4.10 if you are at the drag strip.

Apparently the 3.73 is a "torsen" branded diff? Not sure what that means?

* Couldn't tell much of a difference between the 3.55 and 3.73 when I test drove them.