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Interesting content video put out by Steeda recently. They did a deep dive as to what might be the best gearing for an autocross course. Essentially, they came up with putting in 3.73 rear diff, and just leaving it in 3rd for all the turns and into the straightaways...instead of 3.15 shifting back and forth between 2nd and 3rd. They go into a little more detail on it (like how tire diameter comes into play), but was wondering what the autocrossers think might think of this.

 

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I saw that vid the other day.

I think it entirely depends on the courses you frequent. The clubs I run with rarely has a course with enough straight to get me out of 2nd with the 3.55 PP rear gears. Since I also daily drive mine, you couldn't pay me to go to 3.73 gears. I think they're appropriate in the cars they get them from the factory, with the V8.
 
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2018 Base Ecoboost, Stock/Factory Tune, M/T Tires
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I haven't seen any aftermarket gears (or axles) to fit our OEM 3:15 housing. Did they make any reference to a vendor?
I'm currently running a smaller wheel and shorter tire (275/40R 17) to help offset my 3:15 gear.
 

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For Street class SCCA this is not an option. SCCA national courses are setup for max speeds of about 60mph so 2nd gear in most cars is all you ever need.

I’m just at the start of sorting a 2020 HPP and handling package car.

The options I see are moving to 18’ wheels and down on side wall to 30-35mm if 2nd gear needs more punch to get off the corner. That worked really well on the last turbo car I sorted in street class.

Old car



New car


Wrap to this


Sent from my iPad using Tapatalk
 

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I haven't seen any aftermarket gears (or axles) to fit our OEM 3:15 housing. Did they make any reference to a vendor?
I'm currently running a smaller wheel and shorter tire (275/40R 17) to help offset my 3:15 gear.
It's the differential that is different for the 3.15 gears. The housing and axles are the same. As the gears become numerically smaller the diameter of the pinion gear gets larger which requires the differential to move more to the driver's side. For the 3.15 gears there is not enough adjustment in the housing to move the diff over enough to accommodate the diameter of the 3.15 pinion. The solution was to cast/machine the flange the ring gear bolts to 0.3" closer to the driver's side.

So, if your car currently has 3.15 gears and you want to go 3.31 or numerically larger you will need a new differential and the ring & pinion of your choice.

Dave
 
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