Attached is an oil sample from our 1992 (1.6) Mazda Miata Racecar. This was from a 12 hour endurance race plus approximately 1 hour of practice prior to the race. Oil was SN rated Kendall SAE30. Curious to see where You think there is room for improvement? Oil pressure indicates 48-52psi while racing (stock relief pressure), based on this I operate under the assumption that a 40wt will reduce flow, therefor reducing cooling and protection? Look forward to Your comments!