So what is the consensus on this for the old whipple? I contacted Royal purple since i been using that in the engine for 6 years and told them i thought it listed 10w40. Here is what they told me.
"I would stick with the XPR, Max Cycle, and HPS 10W-40 oils, in that preferred order. All will work great, but the tiered pricing of these oils does accurately reflect the performance and protection levels offered by these oils. For absolute best performance and protection, I would likely go with XPR 5W-30 as it offers more than enough protection to drop a viscosity grade, and the lighter oil will allow more efficient operation of the supercharger. If you choose against the XPR, Max Cycle 10W-40, then HPS 10W-40."
Btw... You should see what my dad gave me at thanksgiving to remove the oil from the sc.
Mike