Why dose the 8.1 litter ask for 5W30 shouldn't it need a higer viscosity

Hello,
Oil type depends on many factors, such as the mileage on your vehicle, climate, and type of driving you do.  I would recommend visiting a site such as http://www.valvoline.com and seeing what they recommend for your specific needs.  You can plug in your car and information and check out their results.
Best of luck!
CarGrrl