Originally Posted By: INDYMAC
Originally Posted By: Johnny2Bad
Honda sources the rear diff in the S2000 from Mazda; same unit as found in IRS Mazda Miata, RX-7, RX-8 (although the half shafts are a bit beefier in the S2000 application).
Where did you get this information? I heard a few years ago that it was a KIA 4.10 gear set. I'm not sure about the Torsen LSD though.
Here's what I know:
I can confirm the Kia match (sportage 4x4)on the pinion/ring. I bought my 4.7 set from a Kia dealer after researching autotrader for a VIN to provide them. The mazda rx8 or miata (don't remember) that had this torsen I believe has it specd with 75W140.
I can also say the the tranny was simillar or same as RX-8 and IS lexus if not mistaken and they had 75W90 GL4 specd.
The lube is indeed an issue. As this is a convertable driven in warm climate and also a low torque at low rpm, they wanted the thinnest but at the same time polymer free fluid for the diff to cut losses as 20% is about what you see on this car.
That would give out the most power at that level of viscosity protection which is about the same with base oil viscosity => a lot of film.
So off course any 75W90 would be short in viscosity protection.
First because the high VI would make them a lot thinner at true operating temps.
Second because most if not all 75W90 are syntehtics of group api 3 or 4 which both have less film under pressure compared to a mineral or ester, not to mention they likely also have polymers that give out even more.
Third what's been said. J306 changed and the upper part of the 90 is now cut and relabeled 110. In the past most fluids in that upper part of the 90 were sae90 monogrades GL5 and GL6 for heavy duty.
The recommended multigrade oil for this diff is at the very minimum a 75W110.
As far as monogrades, SAE90 is ok but must be petrol based/low VI, min.16-18.5cSt/close to 110, GL-5+LS ready.
They did a similar thing with the engine oil to maximize output but at least in Europe they also approve 5W40 (besides the 10W30). It should give out more losses, similar or better base oil protection after permanent and temporary shear (at 9k rpm) but more winter capability. Note, no 5W30 is listed ... anywhere. Not to say none of the 5W30's are incompatible, but they do seem consistent in their philosophy to avoid thin base stocks and polymers.