Question #1
Not sure I fully understand the what the RX8 uses for a differential. Found the info below on the UK forum which says it is a "Super-LSD" but it still sounds like more of a Torsen than a clutch pack "LSD". Clutch pack LSD implies that it needs the LSD additive. Torsen implies that it does not.

I usually run Redline gear oil. Redline makes a 75/90 gear oil that contains the LSD additive AND a "NS" option that does not and is more appropriate for Torsen differentials. In the Spec Miata world where we run the Torsen, it is recommended to run the NS oil.

Which is the correct Redline oil for the stock RX8 diff?
Should I consider any other brand?

Question #2
For actual 20-40 minute races and/or 7-8 hour endurance racing, what is the recommended oil weight for the stock diff? I have the 4.77. Should I run something heavier than a 90 weight oil to keep it cool? I suspect the 90 weight or an 80/90 is sufficient.

Thanks.

 

the oem rx8 diff is a tochigi fuji super lsd. a hybrid cone clutch type differential. i have always used mobil 1 75W-90 gear oil, with and without LS additive, and it has done fine with ~30 minute track sessions, always comes out looking healthy (especially compared to the transmission oil!). your 4.77 diff should have the finned cover which is nice. i would check on the facebook rx8 autocross and road racing group, there are some enduro rx8s there.

 

Thanks for the input. Was thinking of posting there but wanted to try here first.

Been enjoying your videos btw

 

Thanks man!

 

Do not run the LS additive, the craptacular stock diff needs all the help it can get with locking up.

 

I have always ran Redline 75w-90 GL5 with no issues. Compared to Mobil 1 which I have used and is good for daily driving. I believe for your goals the Redline would be the way to go.

 

I'm having a tough time finding any 75W-90 GL5 gear oil WITHOUT LS additive - what do you use, and where do you get it?

 

The 75W90 NS version is what I preferred to use for autox.

Redline also offers a 75W140 NS. If you don’t have a diff cooler setup it would be my choice for a track car.
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something to be on the look out for with a factory LSD.

https://www.rx8club.com/new-member-f...y-diff-270191/

If you start finding these pieces with a diff oil change then time to upgrade to an OS Giken LSD. Be sure to use their specific OW250 LSD oil with it.
.

 

I think the Motul Gear 300 is a GL-5 without the LS additive.

I just used some Mobil1 with the LS additive in mine after searching around as it seemed to be the generally acceptable answer.

 

Thanks Doc for the confirmation


@hufflepuff
google for Redline 75W90 NS as Team mentioned. Oddly enough, I don't see it on Redline's website but can find it easily on Amazon.


Thanks Team for the reference to the 75/140 NS. Might try some of that.

 

Just in case it wasn’t clear to some people, the Redline “NS” gear oil designation means it doesn’t have the slip additive (NS = NonSlip)

https://www.pegasusautoracing.com/pr...?Product=RL002
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I use Torco and you have to add the LS additive if you want to use it.

https://torcousa.com/collections/tor...acing-gear-oil

 

Can you please explain why you believe that is (LS additive addition)?
.

 

because it states it on the page.

“Note: For limited-slip or positraction differentials use Torco Limited Slip Friction Modifier Type F (for all applications except GM) or Type G (for all GM applications)”

So if you your application calls for the additive… you add it. This would be another option since it doesn’t have the friction modifier included.

 

That’s why I was asking, but it’s just a generic suggestion. I misinterpreted “have to add” like it was sort of a specific warning or something.

 

We used Motul Gear 300.

We blew up the stock diff like Mark said, it shed one of the half moons shortly before nats last year then I drained it after nats and got more of them with metallic paste. When I opened it to put in an OS Giken the LSD was eating itself.