How-To: Change final drive ratio (relatively) cheaply

[Mr.]

Thanks man I subbed to your original post and I am glad that you have done this. This is one of BEST na upgrades you can do. Do you felt like it was a 20 percent increase in torque? Also, could you post some pictures and a videos if you could? Thanks!

[Stevo22]

Another stupid question. If I have a manual transmission do I have to have a manual carrier?

[PantsDants]

Originally Posted by Mr.

Thanks man I subbed to your original post and I am glad that you have done this. This is one of BEST na upgrades you can do. Do you felt like it was a 20 percent increase in torque? Also, could you post some pictures and a videos if you could? Thanks!

Unfortunately I don't really have any pics/video of the installation because I had a shop do everything for me. Differential setup is kind of an art-form though, so if you've never done it before I would recommend having a shop do it for you. As for installing the carrier, that's covered in the service manual and looks to be pretty straightforward, I'm just lazy.

You don't actually gain anything in terms of HP or torque by doing this mod. What you do gain (if you go shorter) is more of your existing crank HP/torque being applied to your wheels. That said, with a 4.88 final drive on the 6AT, it definitely accelerates better. I haven't measured by how much though. It also takes about 500 miles to break in a new gear set so I haven't been able to really get on it and test.

[PantsDants]

Originally Posted by Stevo22

Another stupid question. If I have a manual transmission do I have to have a manual carrier?

Nope, and not a stupid question. The carriers are identical between the two, the only difference is the ring and pinion installed in them from the factory. Manual has a 3.7, automatic has a 3.9.

[uncivilised]

I may add onto this for people in other countries.

I'm in Australia and I just picked up my is300 diff. Its labeled as a M22 with a finned carrier (Australia only got auto is300's, firewall build plate says B04B). I opened the back cover and confirmed its a Torsen LSD

Thinking I got the wrong diff I checked out another is300 a few streets away. I did a quick peek underneath and it also had a finned carrier.

Everything else looks the same like the back cover and the top of the diff. ill compare measurements to my 86 when i can.

[PantsDants]

Originally Posted by uncivilised

I may add onto this for people in other countries.

I'm in Australia and I just picked up my is300 diff. Its labeled as a M22 with a finned carrier (Australia only got auto is300's, firewall build plate says B04B). I opened the back cover and confirmed its a Torsen LSD

Thinking I got the wrong diff I checked out another is300 a few streets away. I did a quick peek underneath and it also had a finned carrier.

Everything else looks the same like the back cover and the top of the diff. ill compare measurements to my 86 when i can.

I've not heard of an M22 coded axle. Searching Amayama, the European-spec IS300 lists 41110-53140 as the part number for the carrier. Comes stock with a 3.5 something final gear. Googling that part number doesn't come up with much though.

This looks like a job for @Jeff Lange: Does this carrier work as well?

[Jive Turkey]

so would you say this setup is better/the same as the Cusco ring and pinion set?

[PantsDants]

Originally Posted by Jive Turkey

so would you say this setup is better/the same as the Cusco ring and pinion set?

It's exactly the same if you get the same final drive ratio, but much cheaper to go this route. Around $325 for parts versus $1000 or whatever the cusco costs these days.

[PantsDants]

Shameless plug: If anyone wants to buy a 3.9 ring and pinion or a spare carrier, let me know, I'm selling both.

[Fast_Freddy]

Any regrets on the 4.88 ratio? I'm leaning toward 4.56 but 4.88 is a possibility since I have a AT like you.

[Tye300]

I also have an AT but went 4.55, how big of a difference is the 4.88?

[Anthony]

I'm thinking 4.88 for a manual. *flexes*

[PantsDants]

Still haven't gotten the opportunity to really thrash on it yet, about 100 more miles to go til we change the oil out. That said, I like it, it was definitely worth it to me. I haven't spun the tires on accident or anything so it's not ridiculous, but it has surprised me a couple times just putting around and getting up to speed faster than I expected. Now 5.71... THAT would be ridiculous.

[PantsDants]

Originally Posted by Anthony

I'm thinking 4.88 for a manual. *flexes*

Hahaha, with the automatic and 4.88, first tops out at like 23 mph. Manual would just be silly. At least I don't have to shift if I don't feel like it.