I have no idea why any thinking individual would say that, but I do all my break ins with the same oil I always run. That happens to be Amsoil MCF full synthetic.
Hot cams says not to use synthetic oil for the break in the problem is I only run synthetic does it matter?
In general, there are two things you need to observe regarding cam break-in:
- Use a moly assembly lube. Not gobs of it, just a coating on the lobes. Drench the lifters with your engine oil before you close up.
- Keep the engine above 2000 RPM for the first 15~20 minutes. Improves lubrication and reduces scrubbing the new lobe surface.
Ideally, you would replace all the lifters, too. You don't have to, but it is the best approach. If any of them look worn or "wavy" on top, get new ones.