Switching from 87 to 93 octane

07AlloyGT · Mar 14, 2008

Ok folks, I need some advice. I finally added my 93 octane tune that I got from Brenspeed. I filled up with gas (93 octane), then immediately added the tune. Then I couldn't wait to try it out. From a dead stop there seems to be some loud pinging in the engine, much like my 89 GT does when I run anything lower than 93 octane. Could this possibly be because there was still some 87 octane gas in the tank? I ran it down to about a 1/4 of a tank. Do I need to run a couple of tanks full of the 93 octane, before I continue to stomp on the gas again? Any advise?

COBESGT · Mar 14, 2008

Octane would be less than 93

07AlloyGT said:
Could this possibly be because there was still some 87 octane gas in the tank? I ran it down to about a 1/4 of a tank. Do I need to run a couple of tanks full of the 93 octane, before I continue to stomp on the gas again? Any advise?

I don't have the tuner experience, but I would think that your problem is that you really don't have 93 octane in the tank. If you still had 1/4 tank of 87 octane and mixed that with 93, you might be somwhere around 91 octane. Real rough estimate below.

93 - 87 = 6 octane points difference
6 / 4 (quaters in a tank) = 1.5 octane points per 1/4 tank when diluted
93 - 1.5 = 91.5 octane

Maybe you could choose the 91 octane tune (if you have it). When I spoke with Brenspeed, they told me you should run at least one full tank of a certain octane before switching over tunes, so it doesn't get diluted. Hope this helps.

99GTtony · Mar 14, 2008

When you go from running a lower octane to a higher octane/tune, you need to go through a couple of tanks of the new fuel before switching yout tune. The older fuel will dilute the new higher octane rated fuel until it is all gone. That's why you have pinging.

DarkFireGT · Mar 14, 2008

1/4 tank was NOT low enough. Put it to a 89 or 91 tune right now so you don't harm your engine.

You need to run it all the way down. When the message center shows 0 miles to empty, you have 15 to 20. So try to get as close to 0 as you can. That's plenty, especially now, since you've already mixed in some 93. This is what Doug@Bamachips suggested when I switched to 93.

Snooze · Mar 14, 2008

DarkFireGT said:
1/4 tank was NOT low enough. Put it to a 89 or 91 tune right now so you don't harm your engine.

You need to run it all the way down. When the message center shows 0 miles to empty, you have 15 to 20. So try to get as close to 0 as you can. That's plenty, especially now, since you've already mixed in some 93. This is what Doug@Bamachips suggested when I switched to 93.

100%. now Go go go! Stop reading this *****, and fix that tuner!

07AlloyGT · Mar 15, 2008

Thanks for all the feedback guys. I changed to the 87 tune as soon as I read your replies yesterday. I only put about 20 miles on the car after setting up the 93 octane tune. And I only laid the hammer down that one time when I heard the pinging and let off IMMEDIATELY. So since my tank is full now with 1/4 tank of 87 octane and 3/4 tank of 93 octane, am I safe to at least switch to the 91 octane tune for now?

Snooze · Mar 15, 2008

Just play it safe. This is Your car we're talking about anyways! Go for a couple of cruises around the town, fill up with 93 again. Then you can be sure that your not killing your engine and sleep sound at night.

DarkFireGT · Mar 15, 2008

07AlloyGT said:
Thanks for all the feedback guys. I changed to the 87 tune as soon as I read your replies yesterday. I only put about 20 miles on the car after setting up the 93 octane tune. And I only laid the hammer down that one time when I heard the pinging and let off IMMEDIATELY. So since my tank is full now with 1/4 tank of 87 octane and 3/4 tank of 93 octane, am I safe to at least switch to the 91 octane tune for now?

Just stay on the 87 tune until you fill the whole tank with 93. The difference isn't that great. And at least this way, if you wanna drop the hammer, you can without worrying.

ranger04 · Mar 16, 2008

Would a can of octane booster help if he assed it now?

DarkFireGT · Mar 16, 2008

NO NO NO NO NO!!!

Octane booster is TERRIBLE for these cars. The car will run like crap and he'll need new spark plugs. I've said it many times, and just saw someone the other day put octane booster in and have to replace their spark plugs. Do not put that junk in your car.

Switching from 87 to 93 octane

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