Just read a UOA here for a Corvette on Mobil1 5w-30. Blackstone said that the 16ppm Si was "fine". I've read other posts, though, in which some have stated concerns at Si levels in the high teens. At what level does the red flag go up for you? Are there trends associated with engines? Manufacturers? Aside from the problems occasionally evidenced by use of oiled elements like the K&N, in a stock air system with a new or clean paper filter, what range of Si values do you hold as acceptable?