Depends on what height tires you use. I am sure Terry and Jason's gear recommendations are based on 315/30r18 height tires. That's why I swapped to 3.31s, although I would prefer that gear with the factory manifold even with the factory height tire.
We came up with this 3.31 ratio recommendation (for 5.0 + Getrag) based on multiple tires in the 25.5-26.5" height range, which encompasses most aftermarket 18" sizes that fit these S197 cars.
- Most of the wide 18" sizes are 25.5" tall: 275/35/18, 295/30/18, 315/30/18, and 335/30/18 Hoosiers are all within 0-0.1" of this height
- Another popular size: 275/40/18 = 26.7" tall
- 285/35/18 (of which there are painfully few to choose from) = 25.9" tall
- 295/35/18 (again, too few to choose from) = 26.1" tall
- 345/35/18 monster rear Hoosier is only 26.8" tall. That change made the car SO much easier to autocross and drive on track... softening the effective rear gear ratio, and of course giving us 13.2" of tread on the ground (shown above).
Well with the 5.0L motor and the Getrag 6-speed gearing, plus those tire heights, the 3.55 and 3.73 ratios MAKE NO SENSE WHATSOEVER. We have had a hard time trying to understand the reasoning at Ford for using these ratios... other than "that's what we used before", with the T45 and other transmissions. Just like there are "legacy" parts made for this chassis that make no sense to us (torque arms, bump steer kits), Ford used some "Legacy" rear ratios.
Maybe it works for a drag racer, who switches to a TALLER rear tire. But for the wider tire sizes that work on track or in autocross, WHICH IS THE WHOLE POINT OF THIS SUBFORUM, the 3.31 is the ratio that works. It extends 2nd gear in an autocross and reduces how many shifts you make in 3.73 or 3.55 geared cars on track. Torque at the wheels isn't an issue with 3.31s on the 5.0L powered cars, and you can't almost ever have enough tire to use what there is in low speed (2nd gear) corners anyway.
My HPDE1 student this past weekend had 3.73s in his 2012 Boss302 and it was always running out of gear, and a 3.31 gear would have given him more choices and less shifting. I've driven too many 5.0L Coyotes with the Getrag on track and I always feel like I'm in the wrong gear in 3.55 and 3.73 cars. Always.
anyway, sorry for the thread jack... just had some right seat time in a 3.73 geared car on track this past weekend - which reinforced our calculations and recommendations for the past 6+ years once again.
Now when you put in a real transmission in these cars, like the
T56 Magnum XL (with the optional 2.66 1st and 0.5 6th), ALL of that goes out the window. THIS transmission is when the 3.73 rear gear feels "right" on track and with street use. The internal gear ratios are VERY different than the Getrag MT82. The T56 Magnum has 2 overdrives, and 4th is 1:1 (with the Getrag 5th is 1:1).
Cheers,
