Installation Time: Afternoon
February 29, 2016
Decent performance increase
This modification was much needed over the 2.73. I have also installed the solid one piece drive shaft as well. To start it off, I am using my 2nd Bama performance tune. The first would keep me in 1st until 3k RPM...awesome performance, less great for mpg especially annoying/jerky in parking lots and slow spots. Unfortunately I do have a small amount of noticeable gear whine in 1st, and reverse is...like whoa. People have actually asked about it while riding with me. I attribute this to the install though and it in no way reflects negatively on the part. Honestly, it doesn't bother me...but from what I have read is that once driven like this for a bit...its permanent. So, be aware of that. I used all Ford Racing parts/kit and bearings etc for install and Royal Purple fluid.
Nitty gritty, performance increase is FOR SURE noticeable. I half wish I would have chosen the 3.73, but this is good as I do a few miles on the highway every day to work and back. For those saying no notice in mpg...they are lying, or just not tracking it very well. I track my mileage religiously. After my other upgrades I was averaging 22-23mpg driving normally, but getting on it somewhat often. After new shaft/gears lowest is around 18.5-19 I just drove like a grandma for a week (mostly 2.5k rpm starts and no excessive playing at higher speeds) and the results are in. I filled up around a quarter tank and averaged 20.94mpg. At this point if I use a full tank I may average 21-21.5. I do a lot of city cruising 45-50 and limited interstate driving at 70-75. A lot depends on the tune you use as well. I am more near factory shift points than not. With a typical tune for this ratio from Bama, expect less mileage. Though, the performance is much better off the line compared to the more stock tune I use now.
All in all, if you are thinking about this just do it. The 3.31 may not be enough of a kick to make it worth it, yet the 3.73 may reduce your mileage a lot if you drive on the highway often. The 3.55 is a good in between for performance/mileage and I am mostly satisfied with it in those regards. If you have the extra coinage, have a dealership install it. A Ford dealership will guarantee 3 year 36k mile and there will be no whine. My local dealers wanted $750 and one wanted $1100 (JUST labor) I paid $400. I am very happy, and this along with the shaft are the best upgrades I have done to date.