I tried it, runs suggested it was probably .02 quicker in the quarter. That was going from 20W-50 Valvoline to Amsoil 10W-30 back in the mid 90's. It is also a good test on how well your rear main is sealed up. Bearings looked pretty much the same. I believe synthetics are better oils but IMO not worth the hi cost. I went back to the 20W-50 Valvoline and am still running it. I never used anything other than my judgement to determine change intervals. I try to change every 50 - 60 passes. This is my