Installed 3.91 rear diff from Lexus is300- amazing

[bababooey]

thanks I was rather clueless to how the ratio changes in either direction. your explanation makes sense. ive seen it as an dealer option sometimes when building new makes over the web.

[fika84]

Originally Posted by nocoolname

Does the BRZ use a 8" ring gear as well? I read somewhere once of being able to use the 8" gear sets for a Toyota pick-up in the IS300 housing. If the pinion shaft was the same length and spline for the BRZ flange then it could be some cheap gear swaps.

I was curious about this as well... I wasn't able to find any hard evidence (like matching part#'s) that would lead me to believe that it would work.. so I went with the known gear choice that works from the 1986.5-92 Supra from Weir Performance.. the price really isn't that bad all in all compared to pickup truck solutions. Maybe @mrk1 has more info on the topic.

[Flateightysix]

Originally Posted by ogrowup

I just swapped out my stock 4.10 diff for the 3.91 harvested from a Lexus is300. The difference was profound.

I have a Ptuning turbo kit with e85 and it dyno'd at 430whp. Fast as hell. I have the Clutchmaster RX300 clutch. I love the car but I've never really been happy with how choppy it felt. Not terribly smooth engaging 1st gear, and when I'd lift off the gas there was a noticeable deceleration. I'd also find myself wishing there was a 7th gear, as I'd be at 3000 rpm at 70mph.

After doing some research I learned the diff swap from the Lexus was pretty much a bolt on. I figured I would give it a shot. The result : Awesome in every respect. The caveat is- this only applies to boosted 86's not NA. With the new diff the car is slicker than snot in first gear, super easy to drive in town, I can stay in each gear longer so the turbo spools up better, and at 76mph I'm at 3100 RPM. For me, the is the missing link. The car just glides, super smooth delivery of power, and wicked fast without the nervous and choppy feel of the lower gear ratio ( 4.10)

I'm a happy dude.

Was it baisically a straight swap? Having difficulty finding a good answer on the forums. Really curious if internals could be swapped to our diff have a GReddy high capacity diff cover would love to hold on to

[Irace86.2.0]

If I was pushing that much power I would probably want longer gears too.

[Flateightysix]

Originally Posted by Irace86.2.0

If I was pushing that much power I would probably want longer gears too.

Yeah I’m at 400 now and would love something that. would stretch first out for sure and lower cruising speeds rpm’s on the highway


Sent from my iPhone using Tapatalk

[projectXTR]

So if I get it right, IF you have power levels that overwhelm your tires and thus traction, you can swap to a lower FD like this one. Meaning you'll have better traction, and possibly have better acceleration.

@OP : did you end up timing the difference between stock and this FD with your setup for something like 0-60 or 0-100?

[Alltezza]

Is this a pretty straight forward bolt on process? I'm actually thinking of doing this now my rear end loves to break loose.....I also miss flooring it on 1st-2nd gear

[tyler_win_photo]

Originally Posted by projectXTR

So if I get it right, IF you have power levels that overwhelm your tires and thus traction, you can swap to a lower FD like this one. Meaning you'll have better traction, and possibly have better acceleration.

@OP : did you end up timing the difference between stock and this FD with your setup for something like 0-60 or 0-100?

Yes in a sense. The lower FD allows you to put the power to the ground easier. Also for manual transmission turbo applications, short gear ratios are not ideal as you're constantly dropping out of boost between shifts.

It's one of the reasons why a turbo manual transmission twin that makes the same amount of power as a turbo automatic transmission twin will lose in a roll race. While NA, the manual would destroy the automatic.

[Freddy@PTUNING]

Yes, the IS300 rear diff is a direct swap. The OP has since swapped back to the stock diff.

[StraightOuttaCanadaEh]

Originally Posted by Freddy@PTUNING

Yes, the IS300 rear diff is a direct swap. The OP has since swapped back to the stock diff.

why'd he swap back?

[Alltezza]

Curious to know this as well, I've been hunting for IS300 diffs now.

[Flateightysix]

I would be curious also why he swapped 🧐


Sent from my iPhone using Tapatalk

[Freddy@PTUNING]

I can't remember exactly but IIRC he preferred the shorter gearing in the higher gears.

[Sonic86]

For those of you guys who drives a lot of freeways on their manual cars :-)

I daily drive my 86 (100-160 miles every day) and it's turbocharged.
Since my 2017 86 MT comes with 4.3 FD from the factory long distance rides were pretty annoying.

So I was looking for the way how to lower final drive in order to lower RPMs and increase freeway speeds and fuel economy.

Did some research and figured out that 3.58 is the lowest possible gear ratio for our differential.

So I bought ring and pinion gears and installation hardware from Nitro Gears.

Done everything by myself in my own garage. It wasn't easy but youtube helped a lot.

I also got a bit more comfortable tires - 225/45R17.

As a result - freeway long distance rides are very comfortable, just like on automatic transmission cars.
70mph on 6th gear engine revs are 2700 rpm. Before it's been doing like 3000 rpm at 65mph.

Here is the speed comparison chart for 4.3 and 3.58 final drive ratios:

PS: 0-60 time is still decent :-)