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Engine, Exhaust, Transmission Discuss the FR-S | 86 | BRZ engine, exhaust and drivetrain.


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Old 09-09-2019, 09:59 AM   #57
DIE1000DEATHS
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Originally Posted by Gam3rBlue View Post
Doing this swap, Is it only good for Turbos or should It also be done for SC pushing 350whp? Lemme know, If its worth it.


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It would be fine for that application too. It will help if you have traction issues in the lower gears, and simply give you more time in them (and all gears really)
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Old 09-17-2019, 01:15 PM   #58
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I'm turbo'd on a 2017 with the 4.3 diff. Would it make a noticeable difference to swap to the 4.1 diff? Can I just swap internals or do I need a whole diff?

My second gear feels really short now and I'd like to drop my hwy rpms a little.

TIA
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Old 09-18-2019, 12:15 AM   #59
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Originally Posted by MotoX16 View Post
I'm turbo'd on a 2017 with the 4.3 diff. Would it make a noticeable difference to swap to the 4.1 diff? Can I just swap internals or do I need a whole diff?

My second gear feels really short now and I'd like to drop my hwy rpms a little.

TIA
Oh man I'd swap you a 4.1 diff with 37k miles for your 4.3 diff. You can just swap the ring and pinion final drive gears if you take yours off and open it up.
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Old 09-18-2019, 06:20 PM   #60
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Quote:
Originally Posted by MotoX16 View Post
I'm turbo'd on a 2017 with the 4.3 diff. Would it make a noticeable difference to swap to the 4.1 diff? Can I just swap internals or do I need a whole diff?

My second gear feels really short now and I'd like to drop my hwy rpms a little.

TIA
Yes that would make it feel great. I’d trade with someone local on the forums. Just make sure the 4.1 is low mile too.

I’d swap the entire housing with someone, but upgrade the bushings on the 4.1 as it seems the 4.3 came with superior front bushings. I’d do sti front and rear diff bushings but that’s just me haha.
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Old 09-18-2019, 09:03 PM   #61
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Originally Posted by MotoX16 View Post
I'm turbo'd on a 2017 with the 4.3 diff. Would it make a noticeable difference to swap to the 4.1 diff? Can I just swap internals or do I need a whole diff?

My second gear feels really short now and I'd like to drop my hwy rpms a little.

TIA
It makes every gear 5% longer/less aggressive. Generally recommended for FI. But depends on a lot of factors.
How much power are you making?
What is your reasoning for wanting to swap?

4.1 FD assemblies are cheap. Under 400$ for low mileage. Just buy one and have the option of going back to stock or sell the 4.3 assembly for a tiny profit.
Depending on the above answers some people even go to 3.9 or 3.7 FD as its a direct swap.
For general street hooning id say
Sub 215whp 4.56
215-250whp 4.3
250-325whp 4.1
325-400whp 3.9
400+whp 3.7


But if tracking/autox/drag then its an entirely different scenario.
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Old 09-18-2019, 09:55 PM   #62
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Originally Posted by 86TOYO2k17 View Post
It makes every gear 5% longer/less aggressive. Generally recommended for FI. But depends on a lot of factors.
How much power are you making?
What is your reasoning for wanting to swap?

4.1 FD assemblies are cheap. Under 400$ for low mileage. Just buy one and have the option of going back to stock or sell the 4.3 assembly for a tiny profit.
Depending on the above answers some people even go to 3.9 or 3.7 FD as its a direct swap.
For general street hooning id say
Sub 215whp 4.56
215-250whp 4.3
250-325whp 4.1
325-400whp 3.9
400+whp 3.7


But if tracking/autox/drag then its an entirely different scenario.

I'm making about 330 on e85. The car is mostly a daily driver but it might see 1-2 track days per year. I'll look around locally and see if I can find a 4.1 diff to buy, it'd be nice to have both in case I ever want to swap back.

Thanks for the help!
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Old 09-18-2019, 10:32 PM   #63
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Originally Posted by MotoX16 View Post
I'm making about 330 on e85. The car is mostly a daily driver but it might see 1-2 track days per year. I'll look around locally and see if I can find a 4.1 diff to buy, it'd be nice to have both in case I ever want to swap back.

Thanks for the help!
Exactly!

I got the spare 4.1 diff assembly from Ebay for $200 shipped! And it takes about 30 minutes to swap it. So I keep it in case I need to go to the track.

Swapping pinion/ring gear set is a pain in the neck...

PS: I'm making 260-280whp and I got 3.58 FD for a daily driving and I'm loving it cause it feels like I got the 7th speed
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Old 03-18-2020, 05:14 PM   #64
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Originally Posted by Sonic86 View Post
Exactly!

I got the spare 4.1 diff assembly from Ebay for $200 shipped! And it takes about 30 minutes to swap it. So I keep it in case I need to go to the track.

Swapping pinion/ring gear set is a pain in the neck...

PS: I'm making 260-280whp and I got 3.58 FD for a daily driving and I'm loving it cause it feels like I got the 7th speed
Which pinion/ring gear did you buy on Nitro gear? I'm possibly looking into a 3.91.

Cheers!
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Old 06-29-2020, 11:46 PM   #65
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So I’m strongly considering this swap. I have a boosted (turbo) manual FRS, tuned on E85. I found an M85 LSD locally for a decent price, with 180k miles on it. My car is a DD, not tracked. I’m trying to decide between the 3.7 and 3.9 LSDs. Any big concern going with the M85?
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Old 06-30-2020, 01:00 AM   #66
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Originally Posted by kmbkk View Post
So I’m strongly considering this swap. I have a boosted (turbo) manual FRS, tuned on E85. I found an M85 LSD locally for a decent price, with 180k miles on it. My car is a DD, not tracked. I’m trying to decide between the 3.7 and 3.9 LSDs. Any big concern going with the M85?
180k miles is quite a bit.
How much power are you making?
What is your expected reasoning for wanting a 3.7 or 3.9?
Is there a speed you normally pull to on hwy pulls? Or would like to be able to pull to? You want the top of your 1-1 gear (5th) to be right at or slightly over whatever speed you want to go to as fast as possible to that speed, but the less aggressive (numerically lower) will be slower at any given speed below the more aggressive (numerically higher) ratio top of 1-1 gear (5th).

assuming stock 24.6 tire diameter.
A 4.1 will be fastest to 130mph
A 3.9 will be fastest to 137mph but slower than 4.1 to 130mph
A 3.7 will be fastest to 144mph but slower than 3.9 to 137mph and 4.1 to 130mph.

This is also assuming starting speed of 0mph and not factoring any traction advantages or disadvantages one has over the other, just purely potential mechanical torque. Also each will have specific speeds in which they are faster. Like a 3.7 in 3rd will be faster than a 4.1 once it’s shifted to 4th but then lose the advantage once the 3.7 also shifts to 4th etc. so it can get pretty technical and complicated if you want to pick the exact best one for your needs.

Personally to simplify it i just go off what i want my 1-1 gear to hit so i can do pulls to that speed as fast as possible. That’s why i chose a 4.3 with my 25” diam tire i can hit 126mph in 1-1 gear for fun 40/60mph - 120/125mph pulls as fast as possible.

You could technically calculate all of this off your 4th gear and then sort of treat 5 as an overdrive in a sense.
Which would be
4.1 - 107mph
3.9 - 113mph
3.7 - 119mph with a taller tire could be really good for 120mph pulls.
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Old 07-28-2020, 08:45 AM   #67
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I'm looking to swap R&Ps as I will already have my differential apart to install an OS Giken 1.5way. I want 3.90s, and the best option I've come across thus far are these:

https://www.nitro-gear.com/Toyota-8-.../t8-390-ng.htm

Now the above link retains 27 spline setup, so I think this should be a drop in install using the oem yoke flange and a new seal/crush sleeve.

There's also this one which upgrades you to a 29 spline setup, which means you'd need their yoke kit. Unsure on if this would be a bolt in install, or if there'd be spacers/shims required.

https://www.nitro-gear.com/Toyota-8-...-390-29-ng.htm

I would be interesting to have the 3.90/3.91 OEM is300 part numbers to check dealer pricing on new R&Ps as another route to explore.
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Old 07-28-2020, 08:49 AM   #68
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If anyone interested, I have an OEM 3.7 diff in the member classifieds section.

https://www.ft86club.com/forums/showthread.php?t=141509
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Old 07-29-2020, 07:34 AM   #69
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After some more researching, it looks like the following items would be needed to do the swap if you're going with nitro gears:

https://www.justdifferentials.com/To...-390-29-ng.htm

https://www.justdifferentials.com/To...tlc100-ifs.htm

https://www.justdifferentials.com/YO...yfitkit-29.htm

https://www.justdifferentials.com/SKCSTV6-p/skcstv6.htm

Was more than I had expected with all the install parts included, but if you're already cracking the case to install a clutched aftermarket diff, I'm not sure there are any more cost effective solutions. Total is ~ $750 USD
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Old 07-29-2020, 02:27 PM   #70
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Quote:
Originally Posted by mhiscott View Post
After some more researching, it looks like the following items would be needed to do the swap if you're going with nitro gears:

https://www.justdifferentials.com/To...-390-29-ng.htm

https://www.justdifferentials.com/To...tlc100-ifs.htm

https://www.justdifferentials.com/YO...yfitkit-29.htm

https://www.justdifferentials.com/SKCSTV6-p/skcstv6.htm

Was more than I had expected with all the install parts included, but if you're already cracking the case to install a clutched aftermarket diff, I'm not sure there are any more cost effective solutions. Total is ~ $750 USD
Pretty sure it’s already a 29 spline so don’t need the “fit kit”
You dont need the solid spacer, but it’s recommended uogrsde imo.
And don’t need the seal/bearing kit if your diff is low mileage can reuse. You do need a set of shims but a shop will generally have an assortment available.

M98 rear diff is the oem LSD factory 3.91 FD.
It adds a lot of labor time/expense to swap ring and pinion and crush sleeve and re-shim and set lashing/spacing vs just doing a new LSD. Could even just DIY the LSD swap is giken claims to not mess with spacing/lashing and need re-shimming.
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