Dan, what are the extreme situations. I'm in the south and tracking the car in August with 100 degree air temps and 140 degree track temps caused me to think about using 15W 50 M1 for just that weekend. Someone told me it was a stupid idea so I put the 15W 50 back on the shelf. When do you recommend its use?
For starters, the biggest applications for 15W-50 in a broad sense would be engines built with larger oil clearances (high performance builds), engines with wear (also "large" clearances), or engines that will see very high temps at high loads for long periods of time, risking oil film strenth inadequacies from localized or global overheating. A heavier weight oil will provide a thicker oil film at a given temp, a larger safety margin if you will.
For your application, being a hot track, hot lapping for extended periods of time- I would say you have nothing to lose in switching to the 15W-50 for the day, and only extra safety to gain. The only downsides of 15W-50 would be using it in cold weather [and even the SRT's can get away with this as long as it isnt excessively cold due to their oil/coolant heat exchanger never letting the oil drop below the thermostat temp], or in an engine with such tight oil clearances it cannot adequately flow... and the Viper isnt one of them, even OEM.
