Zinc

Another Amsoil user here. For zinc & phosporous I put 5w-20 Dominator in my race car but they have a wide variety to cover any application.

5 HP difference between oil viscosities is more than one may initially percieve. It's a gain throughout the operating range. Perhaps an applicable analogy would be comparing engine #1 that makes 5 HP more at it's peak to engine #2 that makes 5 HP less at peak rpm, but more up to that point than engine #1. (Area under the curve.) Engine #2 will likely be faster than #1.

Clearance and machining tolerances have an influence on what kind of viscosity, pressure and volume you need.
I use a standard volume/pressure pump!