If one really wants to know, get a OBD scanner that will display real time while driving and test things. I don't really use it for the topic at hand, but I like the BlueDriver OBD scanner. The module plugs into the port and a bluetooth hookup to my iPhone and I can see all sorts of real time stuff going on.
I think in most cases, mid grade would be a pretty balance for the average person. Many of the folks that have the Silverado 1500 with the 6.2 Ecotec use 89 regularly. And that engine has a premium 91 recommendation. In that case, if really working like hauling heavy, towing, or driving hilly terrain, it probably would be wise to use premium 91. The same thing can be said for these turbo motors we are discussing. If one is really going to put the motor thru its paces, probably best to use 91. But for average day to day stuff, 89 should do the trick. Especially if there is a substantial price difference.
And Low Speed Pre Ignition (LSPI) is a common thing with these newer high compression, direct injection motors. It is the primary reason that led to improving the API SN rating on motor oil to API SN+. One doesn't want to risk beating the snot out of their motor and killing it prematurely with LSPI. Running regular should only be used when there is no other choice.
My 2017 2.4L LEA is not turbo, but it does have DI and it has a compression ratio of 11.2:1, darn close to the ratio of the Ecotec 6.2 which GM says should use 91. I would not consider running 87 in it on a regular basis. I use E85 because of the big price advantage, and it has a killer octane rating, but if I was using gasoline it would be mid grade 89. LSPI can affect the LEA 2.4L engine too just like it can affect the 6.2L, not just the turbo engines. Anything running higher compression ratios and direct injection is fair game for LSPI.
Freedom is not the ability to do what you want, but the ability to do what you ought.
2006 Cadillac CTS 3.6
2015 Silverado 2500HD 6.0
2017 Equinox 2.4
Last edited by Copperhead; 05-20-2019 at 11:08 PM.