Spent a few minutes researching and found 2 sites that state that RP's viscosity index rating is 129 *** note to self*** Research VI ratings tomorrow 

All the Viscosity index is for is to tell how stable a product is at different temperatures. In other words, the higher the index, the more stable an oil is when it comes heated...

The new Amsoil racing oil (15-50) has an index of 162

It does not mean a whole lot if you have a temperature control system in place (oil cooler). But if you experience the wide range of operating temps I have seen on the hose boats, it can make all the difference in the world.

I have to get with B-rad to get a link up for Amsoil, just trying to get some little duckies in a row...

GT