Using Mazda as an example, after an epidemic of problems with their 2.3 DISI Turbo engine (Mazdaspeed 3 & Mazdaspeed 6), they've switched the problem engines over to synthetic 5W-40 to eliminate turbo smoking & cylinder #1 rod bearing failure. All other Mazdas are spec'd for 5W-20 except the turbo models, which were originally spec'd for 5W-30 but are now spec'd for 5W-40 (unofficially). For turbo engines, thicker is better on the hot end. Stay with 5W on the cold end.
As I said in post #6, I'll defer to you guys who know turbos and are suggesting 40 weight, but I've been wondering about the sensors in these variable timing motors running 40 weight when it's speced for 20-30 weight. I'm no expert, but I'd suggest 20 or 30 weight but in a full synthetic to handle the heat.One thing to note--the newer VVT setups are pressure sensitive.
The reason why your buddy is using Royal Purp is because it's used for rebuilt engines. Royal Purp provides little protection and I'm suprised that they even sell it on the the shelves. They even advertise "engine builders choose royal purple". Just watching-out for ya2 Words: ROYAL PURPLE
which oil is right for you?
My buddy has a 500+WHP EVO. He uses Royal Purple. His car can run 101 Octane Fuel or higher (available in Ontario California, if you live nearby) and his car will reach that 500+ mark