I will argue that the sulfated ash (SA) level -- that is the metal content of an oil -- does not matter for intake valve deposits (IVD) in gasoline direct-injection engines. The IVD is mostly composed of coked base oil with ash (metal) additives that doesn't evaporate. It also contains some exhaust particulates (from EGR) etc. However, since the primary building block of the IVD is coked base oil, how much would the SA level really make a difference? The base oil makes roughly 80% of the oil, whereas the ash is only about 1%. Therefore, I will argue that since the IVD is mostly coked base oil, the ash level has a small effect. In order to combat the IVD, the following all help: (1) Higher-quality base oils, such as PAO and POE, or the poor-man's higher-quality base oils such Group III+ and GTL. (2) More antioxidant to reduce the oil coking. (3) More or better detergent and dispersant to keep things clean. (4) More POE or AN to increase the solvency of the oil, which could loosen up some of the coked oil. There doesn't seem to be any research on this other than a faulty Lubrizol field study that compared a superior (Euro IV) low-SAPS oil to an inferior (Euro III) full-SAPS oil, which obviously favored the Euro IV oil, regardless of the SAPS. Any thoughts?