I was using royal purple. I switched mainly because it's hard to find, and to be honest I didn't notice any special performance. I asked a friend if he could suggest an alternative, he told me to try mobile one race. It's not a whole lot cheaper than royal, but easier to find. And the temp change was a pleasant surprise...BTW it's 10-40...and like was mentioned before, changing often is more important than what type. IMHO.