found this in the latest Rockauto newsletter; applicable to EcoBoost engines, but interesting insight on GDI engines, me thinks...
This year brought us a new specification for motor oil; ILSAC GF-6 / API SP. One of the primary goals of the new oil spec is to reduce incidence of two problems gasoline direct injection (GDI) engines have been experiencing.
GDI blasts the fuel directly into the combustion chamber at high pressure. This leaves less time for the air and fuel to mix together. The resulting air/fuel mixture may burn unevenly which may generate a lot of soot. As the pistons move up and down, the soot gets mixed into the motor oil. The soot travels with the motor oil through the engine and causes wear.
The most noticeable wear often occurs between the pins and bushings that hold timing chains together. As the bushing holes wear and enlarge, the timing chains stretch. Eventually the timing chains may stretch to the point that they slip across gear teeth or otherwise are unable to correctly connect the crankshaft to the camshafts. The computer generates a trouble code, the engine goes into limp-in mode and/or the engine stops running. GF-6 / SP oil resists collecting and circulating the harmful soot.
The second problem, low-speed pre-ignition (LSPI), is also related to the uneven burning of air/fuel in GDI engines; specifically, turbocharged GDI engines. When running at relatively low RPM and under heavy load, like when moving away from a dead stop, severe knocking may occur inside the cylinders. Scientists figured out that traces of engine oil mixing and burning with the air/fuel mixture contributes to the damaging engine knock. GF-5 / SN-Plus spec oil was released a couple of years ago to combat this problem (watch for the “Plus” after SN). The new GF-6 / SP oil helps with both the soot and knock problems.
GF-6, API SP and API SN PLUS on label
Ford has produced the most turbocharged GDI engines. Small 1L, three-cylinder Ford EcoBoost engines power Ford Fiestas, and big 3.5L, six-cylinder EcoBoost motors are in work trucks that rack up a lot of severe-duty (towing, dust, etc.) miles. The soot and knock problems have been studied most thoroughly on EcoBoost engines. The new specification actually requires that new GF-6 / SP oils pass tests running in Ford EcoBoost motors!
These new oils, higher fuel injection pressures, intake manifold port injection coupled with GDI, etc. help solve these problems on older engines and prevent them on newer engines. GDI engine owners may be able to help the most by simply changing their vehicles' motor oil frequently and always using the correct oil. Instead of waiting for the longest, light-duty, oil change interval (often 7,000+ miles/11,000+ km), change the oil closer to the severe-duty interval (often 3,000 miles/5,000 km).
You can check to see if your specific vehicle's engine uses GDI by looking at the “Info” pages and part descriptions for the engine's Fuel Injectors found under “Fuel & Air” in the RockAuto.com catalog. Find the correct engine Oil for your vehicle under “Engine.” Oil is also listed by viscosity/weight under the “Tools & Universal Parts” tab.
Note: The “A” in GF-6A means the oil is a viscosity/weight compatible with existing engines. The “B” in GF-B means the oil is only to be used in recent engine designs that require completely new viscosity/weight oils such as 0W-16.