The engines are all the same, whithin 1-4 horsepower of each other unless say one of the cars is completly out of title comtention, they may agree to run an "R&D" engine that would offer more power and a chance to win a race, but may also fail. The engines are turn key, and in the case of Stewart-Haas, their employees never touch the engine other than to install it or remove it. Hendrick engine tuners do any maintenance and adjustments at the track. Hendrick is getting "special formula" motor oil straight from Shell and I'm sure since they are a sponsor, Stewart-Haas is getting the good stuff from Mobil. The fact that HMS cars have lost three engines since the chase started last fall (Gordon 2, Kahne 1) and Stewart Haas has had none is just the luck of the draw.