flg2010

I have a 2008 GT with a steeda CAI and a SCT 89 octane tune.

Will using 91 or 93 octane do anything to performance?

Will using 87 octane without a detune be a problem?

J2L06GT

No help with performance w/higher octane
when using 89 tune, only try higher oct if you
hear pinging, don't go to 87 because it will
probably cause pinging without a retard on timing.

Nuke

Use the octane of the tune. Using a higher octane will not add performance. Using a lower octane will eventually caue engine damage. That's why an 89 tune is called "89". Use it.

flg2010

I also have a 91 and 93 octane tune. I will load up he 91 and use 91 octane and see what happens for performance.

Mudflap

I generally use slightly higher octane than the tune is written for. For example, my Vortech tune is 91, but 93 is widely available here. I do this to account for variations in the gas quality / octane levels, and also in case I drive somewhere that is higher in elevation and has lower octane ratings available overall. Just personal preference on my part... Do not ever use a lower octane # than the tune is written for unless you HAVE to. ie you're in the middle of nowhere and have no choice. If that ever does happen, baby the hell out of it until you can get better gas.

joaquinGT

Never get 87 if you don´t have a tune for it, it will cause engine damage, by the way, check your 93 tune you will feel a difference. In my car I get better gas mileage and the engine runs smoother.