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Former G8 GT owner
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Discussion Starter #1
I have a 91 Vararam Cortex Tune installed on my G8 GT (because most all gas stations where I live carry 91 as their highest grade)

But sometimes when I fill up in different towns, I pull in and notice they don't have 91 as an option.

They have 87 89 93

So I put in 93. Would that have a negative impact of performance for that tank of gas? What about fuel mileage? Remember the car is "tuned" for 91.
 

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Very little problem at all.
 

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594 Posts
No negative impact. However, if you have a 93 tune, I would hesitate using 91 gas often. As for gas mileage, I don't think you will see any difference - good or bad.
 

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Premium Member
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2,286 Posts
On tunes, you shouldnt downgrade octane, but you can upgrade without issues.
 

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Capital City G8
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3,219 Posts
I have a 91 Vararam Cortex Tune installed on my G8 GT (because most all gas stations where I live carry 91 as their highest grade)

But sometimes when I fill up in different towns, I pull in and notice they don't have 91 as an option.

They have 87 89 93

So I put in 93. Would that have a negative impact of performance for that tank of gas? What about fuel mileage? Remember the car is "tuned" for 91.
As other mentioned, no negative impact on using 93 octane on a 91 tune, but you would have problems the other way around.
 
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