Zinc

Amsoil has always been high quality. 6 years ago, I was using 15 50w mobile 1 with a flat tappet cam after break in. After about 50 miles, I noticed a couple of lifters would tap for a few seconds on start up. I called lunati and the tech asked what oil I was using. When I told him, he said lunati didn't recommend using full synthetic oil on flat tappets until they were well broke in. I asked how long. He said 20000 miles! Not sure how true that was but as soon as I went to conventional oil. The problem went away. I use mobile on all my late models with out issue. I should probably quit being so cheap and go roller.