Either the Picco P7-R or the OS VZB V-spec, both mills are reliable and I've run 2 of each for over 10 Imp Gallons each now. All are coupled to JP-2 pipes and run in various buggies, they are most definately serious race engines, easily keeping up with the £500 pro's modded mills. People are going to mention things like the RB's and Nova Rossis, but they are just short life lumps IMO.