Rear Gear Lube - Synthetic Or Conventional?

[1320racer]

Been using Mobil 1 75W-90 Synthetic gear lube for over 2 decades in my bracket cars that see more passes each season than 95% of stock/super stock cars.

My 3144 lb. Firebird that is restricted to run 9.0 every week, 60 foots low 1.20s to high 1 teens with a best to date of 1.17 and has gone 700+ passes without a R&P failure, running out of the box Richmond gears.