If you install aftermarket cams, valve springs, and retainers, do you have to run thinner oil? Another words, lets say Im using 5w-30 now. Will I have to go thinner than that, or thicker like 10w-40? I'd think that thicker oil would cause major problems when building up internals like that.

 

I have a fully built head with Sharkracing 268 cams and a complete Ferrea valetrain (dual springs, titanium retainers etc. etc) and I run the same type of oil as I did when I had a bonestock motor. Doesn't seem to have any complications that I can tell of. Oh and fyi, I use 10w-30.