i'm using 10w-30. running a hughes hyd roller cam and lifters. they say to use that weight oil. i contacted them to ask how important it is to use that weight and they said that it's not that important but i shouldn't use a 15-40 or a 20-50, so that only leaves 10-40. they didn't say why to use those weights only. before going roller i always used 20-50.
