Your user manual should have corresponding instructions on the use of engine oil, there will be a recommended viscosity and multiple applicable viscosities.
In fact, most turbine owners in Japan use 5W40 oil
All of my other turbo 4's have used 5w40 as well even though the factory spec'd 5w20 on them. I find it ludicrous to run a 20wt in a hot turbo engine. My manual only states 0w20 SN or SN+ and 5w30 as acceptable top off. Nothing about running it flat out. Which makes me think this book is just recycled from another platform to save money.