To the OP....higher octane ratings will not harm the engine in any way.....so relax.
There can be diminishing returns though.
In the case of the Cruze, it seems either engine design responds favorably to higher octane numbers.
Evidently, there is enouph available ignition advance to take advantage of the higher knock resistance that 91/93 provides and, because it can 'light the fire' a bit sooner in the compression stroke, you can get the same power with a smaller throttle opening.
That, of course, results in the mpg enhancement and a driveability improvement, often described as a peppier or more response to throttle feeling.
We, as a group, have noticed this is particularily noticeable in high heat, high load (A/C operating) around town driving where engine temperatures are at the upper edge of normal.
The engine has a tendency to 'spark knock' under these conditions and the computer retards the ignition timing to prevent mechanical damage.
The operator notices a delay in throttle response and a mileage decrease that disappears when operating with the higher octanes.
My eco auto around town average increases by a bit more than 3 mpg using 93 in the hot summer months as opposed to 87/89 regular.
But, as soon as ambient temperatures are consistantly below 60 degrees (f) I can match the mileage using 87/89 and because the air is cooler the tendency to retard the timing is reduced and driveability improves.
Moral of the story, for me, 93 for best mileage and driveability above 60 degrees.....come fall, back to regular.
The other side of the coin.....one of my many vehicles is a 97 Chevy C-1500 long cab, long box, 350 v-8 auto.
It doesn't care what octane you pour in it......18 to 21 mpg....cold, hot, fast or slow, runs the same hot or cold, air on or not.
It makes it clear that small displacement engines can show big benefits from small changes, larger displacements (both stock) don't.....or at least, rarely measureable.
Rob
There can be diminishing returns though.
In the case of the Cruze, it seems either engine design responds favorably to higher octane numbers.
Evidently, there is enouph available ignition advance to take advantage of the higher knock resistance that 91/93 provides and, because it can 'light the fire' a bit sooner in the compression stroke, you can get the same power with a smaller throttle opening.
That, of course, results in the mpg enhancement and a driveability improvement, often described as a peppier or more response to throttle feeling.
We, as a group, have noticed this is particularily noticeable in high heat, high load (A/C operating) around town driving where engine temperatures are at the upper edge of normal.
The engine has a tendency to 'spark knock' under these conditions and the computer retards the ignition timing to prevent mechanical damage.
The operator notices a delay in throttle response and a mileage decrease that disappears when operating with the higher octanes.
My eco auto around town average increases by a bit more than 3 mpg using 93 in the hot summer months as opposed to 87/89 regular.
But, as soon as ambient temperatures are consistantly below 60 degrees (f) I can match the mileage using 87/89 and because the air is cooler the tendency to retard the timing is reduced and driveability improves.
Moral of the story, for me, 93 for best mileage and driveability above 60 degrees.....come fall, back to regular.
The other side of the coin.....one of my many vehicles is a 97 Chevy C-1500 long cab, long box, 350 v-8 auto.
It doesn't care what octane you pour in it......18 to 21 mpg....cold, hot, fast or slow, runs the same hot or cold, air on or not.
It makes it clear that small displacement engines can show big benefits from small changes, larger displacements (both stock) don't.....or at least, rarely measureable.
Rob
