Modular 4.6 ...the Royal Purple(crap hands down) will initially show that when fresh its wonderful but after about a 1000miles or so..its broken down and doesnt do any better than mineral oil..this is the result of loading up with sulfer additives. As far as not buying Mobile 1 because of some test results...I be skeptical on where they came from. Mobile 1 is not the worst synthetic..its one of the best. The tests Ive seen done between Amsoil and Mobile 1 are close with Amsoil just a little ahead but not enough to be worth the extra cost of Amsoil. Mobile 1 at Wally World in my neck of the woods is only 19.98 for 5 quarts.