I use Valvoline Non Synthetic oils such as VR1 and NSL oils. As to Synthetic I have used Royal Purple.
As of late last year, I have been involved in 4-5 circle track engines, which the blocks were filled with Hardblok so my first thing was it has to have an oil cooler. Well, With the oils they were running it was not needed and you would be surprised who's bottles they fill (Some in this thread)
http://www.schaefferoil.com/