premium fuel for H6 3.0?

[JD]

There is no mpg penalty. Most cars get better mileage with regular
anyway

Only if they are tuned for regular

 

[Edward Hayes]

There is a penalty for using regular in an engine designed for
premium. In addition there is a power loss penalty.

 

[y_p_w]

There is a penalty for using regular in an engine designed for
premium. In addition there is a power loss penalty.

Aren't there different scenarios? I'd imagine that a normally
aspirated higher-compression engine designed for premium would
be tuned for premium at all times.

If it's a turbocharged engine, cruising at 50 MPH in 5th gear on
a flat surface, it might not make that much of a difference. If
there's no boost, then it's essentially a lower compression ratio
engine without air being force-fed. The timing could only be
advanced so far, so would the sensors detect knock with 87
(R+M)/2 octane unleaded?

Of course I'm not taking any chances. My WRX gets nothing but
91 octane Chevron Supreme.