Oh, and he also said Amsoil 75W140 is the absolute best product you can buy. He said it chalk full of all of the best lubricant additives money can buy.

 

I change diff oil for every 2 track days. Will I still need to run 75W-140 vs. 75W-110?

How is MPG affected over street use?

 

I've been using the Motul 90PA, also for autocross only. I change the diff oil every 15,000kms (9,300 miles).

 

Who's PuddyDad? I gather from the context that he's an authority of some kind on the subject, but can you elaborate?

 

Ben Herne (sp?), his handle is S2KPUDDYDAD.

Sorry, I guess I assumed everyone would know who he is. I suppose he's better known in the Forced Induction forum. He's an older (aka experienced) driveline specialist who makes custom rear ends for specialty cars.

For example, I have the 4.30 geared stage 2 build which includes cryogenically treated gears and cases, a polished gearset, grade 10.9 hardware, and a stainless steel solid collar that will not compress. Given his experience, I believe many of us in the forced induction forum believe him to be an authority on the subject. His custom builds have proven to be rather durable/reliable.

 

I can vouch for Ben (S2kpuddydad) knowing his trade. I had one of his diff's on my old s2k that put down 463 whp. He also told me to use 75w140 on my current NA S2k. I just pick up the Mobil 1 stuff at the store, but I think I'll order some Amsoil for the next change.

 

You can use almost anything in the diff. Just change it frequently and look at the magnetic plug. YMWV

 

M409

Am using this for trial. Seems pretty ok but no chance to do a UOA on it.

Moty's M409 is developed to withstand long duration of hours under high temperature and high load conditions. This product consists of non-polymer, ester type base stocks and chemical structure and molecule weight distribution of each base stock is properly blended in a state of micron level.

Viscosity: 75W140 / 80W250 / S80W190

Container: 1L / 4L / 20L

75W140 80W250 80W190
Kinematic Viscosity(@40℃)　mm2/s 249 368 354
Kinematic Viscosity(@100℃)　mm2/s 32.0 43.0 37.8
Viscosity Index 173 172 155

＜M409（75W140）＞
This item is developed mainly for front engine/front drive cars with LSD and for transmissions of front engine-rear drive cars under urban motoring and light circuit driving. The main development concept of this product is for smooth function of LSD and good shift feeling.

 

I've been using BelRay gear saver. Available at most motorcycle shops in the correct 90w/GL5.

 

I just changed mine from Mobil 1 75W-90 to Mobil 1 75W-140. Cost twice as much. Seemed to notice less whine from the diff, but maybe that's my imagination. Seemed to work fine at the 100 degree temps at California Speedway yesterday.