I'm not sure about the 1.8, but the 1.4T definitely responds to increased octanes in terms of performance and MPG. But in colder weather, the effect of increased octance is less noticable. At least that has been my experience so far.
I use the following criteria based on average temperatures for the upcoming week to determine which octane I use:
-Below ~65-70 degrees F, 87 octane
-From ~70-80 degrees F, 89 octane
-Above 80 degrees F, 91/93 octane
These criteria give me the best combination of performance (or also lack of timing pull under load in hot weather and with A/C use) and cost. As always, YMMV.
As a further note, this is the first vehicle I have used anything other than regular 87 octane, and that was after extensive research into the affects of octane on this specific engine. For most N/A vehicles, I would just stick with 87. But it all depends on the specific engine/application.
I use the following criteria based on average temperatures for the upcoming week to determine which octane I use:
-Below ~65-70 degrees F, 87 octane
-From ~70-80 degrees F, 89 octane
-Above 80 degrees F, 91/93 octane
These criteria give me the best combination of performance (or also lack of timing pull under load in hot weather and with A/C use) and cost. As always, YMMV.
As a further note, this is the first vehicle I have used anything other than regular 87 octane, and that was after extensive research into the affects of octane on this specific engine. For most N/A vehicles, I would just stick with 87. But it all depends on the specific engine/application.
