my 350z is 2008 with the HR engine, I installed a greddy twin turbo kit, pistons and connecting rods forged, Microtech Efi lt-16, Cosworth oil pump, fuel pump, 750cc injectors, etc.. Before making these changes I used 5w-30 Royal Purples, now with these changes in the engine I keep using the same oil or I should change the oil viscosity to a thicker like 10w-40, 20w-50, which should I do?

 

royal purple has show to perform very poorly on these engines who knows why, could be reaction to the metal compounds, a specific force being acted on somewhere, who knows. but you shouldnt be using them for starters. secondly what where your bearing clearances set to when the new bearings where installed? impossible to recommend the correct oil without knowing that.

 

When i went TT on my DE my shop recommended 0w40 Mobil 1 European blend. Its specifically engineered for turbo motors apparently.

Ran it for 4 years with 0 issues at all. (445 hp 395tq on stock block with JWT530 kit)

 

really dosnt apply here though, you didnt have a engine built or pushing really high numbers which are the things that would determine if a thicker oil is needed or not. whatever your clearances are what where set from the factory.

op needs to answer with proper information for accurate recommendation

 

All about the bearing clearances. Don't run your car until you talk to whoever put your short block together and find out what oil to run/what the clearances are.