Optimal Valve Lash

My MPP cam states .028 intake and .032 exhaust cold lash.

Now keep in mind that would be with an iron head. I run aluminum.

currently I run .024 and .028 for lash. My engine builder said this is safe. He felt .028 and .032 was excessive unnecessary lash.



I'm wondering what you guys run or recommend. I'd also like to know how much variation can be achieved and what is optimal for performance.

Last, why do some cams have such tight lash while others like mine have so much?