What differential gears are out there?
 

I've been doing some reading and it's a bit confusing.
I have a 2014 MT. I *think* that means I have 4.10 gears.

Are all the pre 2017 MT and AT cars the same 4.10?
And is it 2017+ that goes to 4.3? For AT and MT?


I need something different. Quite frankly, I dont care which way, as I'm currently bouncing off the rev limiter about 150ft before brake points at half the turns. So a little bit taller would be fine, or a good bit shorter. I'm willing to bet the extra shift with shorter gears will offset the the extra gearing from a shorter ratio, so I doubt there's much performance either way.


Thanks!

The early models 4.1. The refresh MT went to 4.3.

The 2022+ are AT 3.9 MT 4.1. Who knows what future models will do.

4.3 was only in the 17 and up MT

Several companies make 4.556 final drives as well, such as Cusco.

There is also a 4.44 from Mfactory.

Jack's Transmissions has a good chart for reference showing MPH/RPM. OE 4.3 is not on there though.

https://www.jackstransmissions.com/b...ar-ratio-chart

What size tires you on? If on 245/40-17, you might try 235/45-17. Not a huge change, would be like going from 4.1 to 3.97. Small step in the right direction anyway, made a noticeable difference for me at NHMS South Oval last year where I was in same situation as you for both before T1 into the oval, and also before T3. Running reverse stagger 245/40-17 fronts with 235/45-17 rears was a big improvement! This year I was on 245s all around and believe it was costing me a few tenths to half a second :mad0259:

The AT never came with a 3.9 final drive.

Oops. :slap:

Funny you say that. That's exactly how I "solved" the problem. I bumped up to 245/45 and it fixed the problem with the horribly "timing" of the gears.

In about 3 weeks, I'm having a new motor and trans put in, and I suspect the LSD is toast. At this point, it's kind of silly not to throw in a new rear.

If I wasn't replacing everything, I'd stick with the 45 series tire, but I'd rather just get the gearing right and then go the correct sidewall tire. The higher sidewall also raises the car about half an inch. Not good for anything, especially front end grip with the splitter.

Did anything ever come with a 3.90? That would be perfect.

The 4.10 will mean an extra shift. It's fine, but I doubt I'll make up any time since the extra shift at the very end will cancel out the gearing advantage. It just means more shifting and more wear and tear on the weak point (transmissions).

IDK, there is a turn or two where a little more torque would help me rotate. It just doesn't have enough to rotate on some higher speed uphill stuff. If steeper is my only choice, it's my only choice.

The 22+ AT has it right now. https://www.caranddriver.com/subaru/...ubaru-brz_2022

Also, any reason to get an aftermarket cover with extra fluid capacity? It's stockish power levels (intake, headers, exhaust, tune). I guess a drain bolt would be nice.

is there a better fluid to use than OEM?

Got it. I'll keep my eyes out for one, but I'll prob not find a 22 on ebay very easily if it's only AT 22s. I can just get it and swap it later if one comes around

The stock torsen LSD doesn't really have anything to wear out outside an normal open diff. There are just a bunch of little gears in there.

https://www.kmpdrivetrain.com/wp-con...sen-lsd-01.png


You can always just do what I am doing, 4.3 diff, stiffer valve springs, 8K rev limit. YOLO :D

Out of the 4 tracks in my area the 4.3 is better at 2, the 4.1 is better at 2.

Where there is friction, there is wear! The Torsen T2R in my LS FD started acting wonky, going into lock/unlock convulsions on corner exit, not cool... Replaced it with OS Giken 1.5-way, set up with minimal preload (max negative preload IIRC) and accel ramps for more lock under load. WAY better and more transparent in operation than the Torsen. If my BRZ's diff is ever gone into, I'll be getting an OSG for it.

It's probably got over 200 track hours on it at this point, lol.

Yeah, I know mechanical parts can wear. I have never heard of an LSD of anytype wearing out. I'll defer to your experience on this one.

Check Lexus IS250 / IS300 gears / differentials. 3.7 & 3.9 available, housing interchanges with ours (in certain years). Some are LSD, many are open.

oh, they definitely do.