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Old 02-25-2009, 10:46 AM   #1
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Default should I tune for non-texas gasoline?

We get sweet, glorious 93-octane fuel in Texas. However, I frequently run my car at a track in Tulsa where I can only get 91-octane. Sure I can fill up with "purple" at the track, but that's a pain in the ***.

Should I fill up with 91-octane and tune-out any possible detonation, or just back timing off and listen for detonation in my headphones? I hit MBT in every cell, and even went 2* further to see if it added torque or power, without detonation...so I may not need to adjust much.

I know people say a little detonation won't kill the motor immediately...but is that true at the power I'm putting down? I enjoy laughing at all these people who pour tolouline in the tank before they run on the track...but don't think they need it on the street. I don't want to play chemist on something I've spent so much money on.

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Old 02-25-2009, 10:59 AM   #2
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MBT does not give the best power in the real world unless you're using some kind of closed-loop spark control, which of course you're not. Back off a couple degrees across the board as a quick measure.
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Old 02-25-2009, 11:02 AM   #3
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Bring extra 93 with you in your tow vehicle.
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Old 02-25-2009, 11:02 AM   #4
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Originally Posted by The_Pipefather View Post
MBT does not give the best power in the real world unless you're using some kind of closed-loop spark control, which of course you're not. Back off a couple degrees across the board as a quick measure.
It gave the best #'s on the dyno. I'd love to hear the logic on why the biggest # on the dyno doesn't translate into the biggest # on the street.
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Old 02-25-2009, 11:03 AM   #5
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Bring extra 93 with you in your tow vehicle.
I have a tire trailer...I plan on running through 2-tanks of fuel per track day, so its going to take a separate fuel trailer.
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Old 02-25-2009, 11:16 AM   #6
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Gotcha.

Wow, what happens if some douche tries to beat you on the inside in a braking section coming into a corner and blows it?
Do you have a backup to get home?

After you tear off the guy's left arm and beat him to death with it, of course.
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Old 02-25-2009, 11:18 AM   #7
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Gotcha.

Wow, what happens if some douche tries to beat you on the inside in a braking section coming into a corner and blows it.
Do you have a backup to get home?

After you tear off the guy's left arm and beat him to death with it, of course.
I'm running HPDE and TT. I don't have a racecar, bank account, or enough testosterone for wheel-to-wheel racing, yet.
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Old 02-25-2009, 11:43 AM   #8
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That makes sense. I did think your car looked kinda nice to be going fender to fender.
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Old 02-25-2009, 11:38 PM   #9
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Originally Posted by hustler View Post
It gave the best #'s on the dyno. I'd love to hear the logic on why the biggest # on the dyno doesn't translate into the biggest # on the street.

Because your dyno's resolution is worse than how much power you would lose if you were advanced past MBT timing. A number of 1% of peak is what I hear in OEM circles for every 3-5 degrees plus or minus MBT. That's probably a smaller number than the resolution of any kind of commercial dynamometer. Things like ambient temp and pressure, altitude, gasoline octane etc. will always change MBT timing, which can of course be taken care of only by closed-loop control.
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