What differential gears are out there? - Toyota GR86, 86, FR-S and Subaru BRZ Forum & Owners Community

GrandSport · 11-21-2022, 02:03 PM

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!

dragoontwo · 11-21-2022, 02:21 PM

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.

NoHaveMSG · 11-21-2022, 03:12 PM

4.3 was only in the 17 and up MT

villainous_frx · 11-21-2022, 09:04 PM

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

NoHaveMSG · 11-21-2022, 09:09 PM

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

ZDan · 11-22-2022, 08:38 AM

Quote:

Originally Posted by GrandSport

I have a 2014 MT. I *think* that means I have 4.10 gears.
...
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.

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

whataboutbob · 11-22-2022, 08:56 AM

Quote:

Originally Posted by dragoontwo

The early AT was 3.9 with MT being 4.1. The refresh bumped AT to 4.1 and MT to 4.3.

The 2022+ are back to the early numbers. AT 3.9 MT 4.1. Who knows what future models will do.

The AT never came with a 3.9 final drive.

dragoontwo · 11-22-2022, 09:03 AM

Quote:

Originally Posted by whataboutbob

The AT never came with a 3.9 final drive.

Oops.

GrandSport · 11-23-2022, 11:32 AM

Quote:

Originally Posted by ZDan

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

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.

GrandSport · 11-23-2022, 11:35 AM

Quote:

Originally Posted by whataboutbob

The AT never came with a 3.9 final drive.

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.

dragoontwo · 11-23-2022, 11:43 AM

Quote:

Originally Posted by GrandSport

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

GrandSport · 11-23-2022, 11:46 AM

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?

GrandSport · 11-23-2022, 11:47 AM

Quote:

Originally Posted by dragoontwo

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

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

NoHaveMSG · 11-23-2022, 11:52 AM

Quote:

Originally Posted by GrandSport

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.

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.

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

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

11-21-2022, 02:03 PM	#1
GrandSport Senior Member Join Date: Sep 2018 Drives: 13 Viper; 14 BRZ; 90 Miata; 18 AMG Location: TX Posts: 304 Thanks: 65 Thanked 187 Times in 103 Posts Mentioned: 4 Post(s) Tagged: 0 Thread(s)	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! __________________ 2014 BRZ: Full track car. Gutted, caged, coilovers, AP enduro, OMP, bolt ons, aero, etc, 2013 Viper GTS : Tractive Coilovers, ACR sway bars, aero, carbon, exhaust, etc. 1992 NA Spec Miata: 1.6 + 1999 NB Spec Miata: 1.8 w/ all the goodies. 2018 GLE 63 AMG: +800hp whistling AWD TT V8 grocery getter 2016 GX460: IDK. Too reliable to sell. Too boring to use.

11-21-2022, 02:21 PM	#2
dragoontwo Senior Member Join Date: May 2020 Drives: 22 BRZ limited Location: Clarksville TN Posts: 1,183 Thanks: 217 Thanked 990 Times in 521 Posts Mentioned: 7 Post(s) Tagged: 0 Thread(s)	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. Last edited by dragoontwo; 11-22-2022 at 09:04 AM.

11-21-2022, 09:04 PM	#4
villainous_frx Off to the track! Join Date: Mar 2020 Drives: '14 Lava 86, '13 WRB BRZ Location: Canada Posts: 694 Thanks: 1,480 Thanked 1,150 Times in 462 Posts Mentioned: 12 Post(s) Tagged: 0 Thread(s)	Several companies make 4.556 final drives as well, such as Cusco. __________________ ZN6 \| Instagram \| ZC6

11-23-2022, 11:46 AM	#12
GrandSport Senior Member Join Date: Sep 2018 Drives: 13 Viper; 14 BRZ; 90 Miata; 18 AMG Location: TX Posts: 304 Thanks: 65 Thanked 187 Times in 103 Posts Mentioned: 4 Post(s) Tagged: 0 Thread(s)	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? __________________ 2014 BRZ: Full track car. Gutted, caged, coilovers, AP enduro, OMP, bolt ons, aero, etc, 2013 Viper GTS : Tractive Coilovers, ACR sway bars, aero, carbon, exhaust, etc. 1992 NA Spec Miata: 1.6 + 1999 NB Spec Miata: 1.8 w/ all the goodies. 2018 GLE 63 AMG: +800hp whistling AWD TT V8 grocery getter 2016 GX460: IDK. Too reliable to sell. Too boring to use.

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