Diff Gear Change

[Riftur]

I know its been talked about a ton but i have been looking around the threads and cant find it. Whats the diff gear I want to change my 13 FRS AT to for more low end torque? I think it was 4.88 but i forget. Sorry to ask this question when i know its been talked about plenty.

Thanks,

[ichitaka05]

Cusco makes 4.55 final drive. Autofactory makes 4.875 final drive. Just google "final drive ft86club".

[humfrz]

Originally Posted by Riftur

I know its been talked about a ton but i have been looking around the threads and cant find it. Whats the diff gear I want to change my 13 FRS AT to for more low end torque? I think it was 4.88 but i forget. Sorry to ask this question when i know its been talked about plenty.

Thanks,

I reckon that depends on where you want the car to go (do).

After you find out what ratios are out there, you may wish to consult with one of the on-line calculators to figure which one fits your needs best.

http://www.catherineandken.co.uk/sti/tyres.html


humfrz

[Reamer]

I may (probably) be completely wrong about this, but changing the diff won't make the car have any more low-end torque than it already does. However, it'll be the illusion of low-end torque since the shorter gears makes it easier (faster) for the car to get in the higher RPM range where the car's power actually lies. I own a AT and I'm planning on going with 4.88 as well.

[headlikeahole]

Originally Posted by Reamer

I may (probably) be completely wrong about this, but changing the diff won't make the car have any more low-end torque than it already does. However, it'll be the illusion of low-end torque since the shorter gears makes it easier (faster) for the car to get in the higher RPM range where the car's power actually lies. I own a AT and I'm planning on going with 4.88 as well.

You are right about being completely wrong haha. Think of it as changing gears on a bicycle to the largest ring in the back; It isn't just the illusion of torque the larger gear actually produces more torque. Just like the on a bicycle the gear will affect how fast the cyclist will need to peddle to achieve a given speed, and the speeds achievable in any given gear.


In the car that means each gear will be reduced by 5-10 mph so instead of hitting 60 in second gear, you're now hitting 50 (don't know the exact numbers). The increase in torque has nothing to do with "getting into the higher rpm" and everything to do with the physics of gears.

[KoolBRZ]

It won't give your car any more torque or horsepower. That said, it will give you more horsepower per revolution of tire. More important, it will reduce the gap between gears, making it easier to stay in the power, and out of the torque dip. Most people have no idea how abysmally geared the AT's really are. I mean it double-clutches 2nd gear because the stretch between 1st and 2nd is so wide. An AT would have to upgrade to a mythical 5.40 FD to even come close to equaling the MT gears.

I'm getting a 2nd rear carrier rebuilt right now with a 4.88 gearset. I'm currently running a 4.30 and just got 42.1 mpg @ 55 mph on my way down to Sacramento. I'll use the 4.88 for track days and city driving, and the 4.30 for road trips.

[KoolBRZ]

People get all worked up over this because it feels like more power, and it feels like a close-ratio transmission. It doesn't give the motor any more power, but it gives it more leverage, since the motor gets to spin more revs per rev of each tire. The transmission gears don't get any closer together, but the gap between shifts becomes closer, since the motor is spinning faster in every gear.

It's an argument between what you feel, and what is measurable at the crank.

A FD change can actually make a car slower on the track, since it might not stay in the ideal gear through the corners, and the top gear is still too tall for the straightaways.

[Icecreamtruk]

Originally Posted by KoolBRZ

People get all worked up over this because it feels like more power, and it feels like a close-ratio transmission. It doesn't give the motor any more power, but it gives it more leverage, since the motor gets to spin more revs per rev of each tire. The transmission gears don't get any closer together, but the gap between shifts becomes closer, since the motor is spinning faster in every gear.

It's an argument between what you feel, and what is measurable at the crank.

A FD change can actually make a car slower on the track, since it might not stay in the ideal gear through the corners, and the top gear is still too tall for the straightaways.

As someone who runs a 4.88 FD at the track. I can confirm, I think it is slower in some tracks (but faster in others). It really depends on the situation (do I need 6th or not for the straight, do I need to shift mid turn, etc...)

[Riftur]

I do not track my car. I just need a bit faster 0-60 for DD. I was told this is the best way to do it with 4.88 gears. Is this not true?

[Sportsguy83]

Originally Posted by Riftur

I do not track my car. I just need a bit faster 0-60 for DD. I was told this is the best way to do it with 4.88 gears. Is this not true?

Best bang for buck mod on this car is E85 tune with header.

[Reamer]

Originally Posted by Icecreamtruk

As someone who runs a 4.88 FD at the track. I can confirm, I think it is slower in some tracks (but faster in others). It really depends on the situation (do I need 6th or not for the straight, do I need to shift mid turn, etc...)

Do you have AT or MT?

Originally Posted by Sportsguy83

Best bang for buck mod on this car is E85 tune with header.

What about the diff change if you already have those?

[Riftur]

Originally Posted by Reamer

Do you have AT or MT?



What about the diff change if you already have those?

I have an AT and the gear change would be a nice undercover upgrade that wont effect my warranty.

there is not an e85 station close to my house and this is for DD. If i was tracking I would go with e85.

[Icecreamtruk]

Originally Posted by Reamer

Do you have AT or MT?



What about the diff change if you already have those?

I have a MT. It might work better for AT, since that will turn out similar to a 4.5 on a MT and I think the sweetspot is somewhere between 4.3 and 4.5 for a manual (2017 MT models have 4.3 FD, maybe they are onto something?)

[Riftur]

Ok so will the 4.88 gear change make my 0-60 faster in an AT car?