93 Octane MSPNP Gen1 Tune to 91 California Safely - Miata Turbo Forum -Boost cars, acquire cats.

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Old 09-22-2016, 08:22 PM   #1
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Default 93 Octane MSPNP Gen1 Tune to 91 California Safely

Recently relocated from Texas which was the land of 93 octane, where my miata was tuned to that accordingly with my MSPNP Gen1 ECU back way when.​ Now, I have relocated to California and the only gas anywhere near me is 91 octane. I have a track day coming up this weekend and long story short didn't take care of this till now (car has been parked with 93 octane in it). I'm going to be towing the car to the track because of CARB and registration non-op reasons.

Question is what are my options to quickly and safely getting the car to run for my event?
I've considered these options:

1) I've looked at Sunoco 260 GTX/GT etc for mixing 91 octane from the pump to make 93 gas
2) Thunderhill Raceway has 100/91 octane unleaded fuel options so I can just top off there
3) Look at changing timing on the ECU table or whatever is suggested to accomplish the change to 91 safely. (to be honest, never have opened up megasquirt software or plugged into the device, it came pre-dyno tuned to 93 from the previous owner)

If anyone can provide any insight into this I'd appreciate it, for now I'm leaning towards just mixing the fuels together at home/track.
I'd like a more permanent solution to where I can live with the few HP I'd lose to go back to 91 octane safely.

Thanks in advance and I hope this question isn't too stupid.
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Old 09-22-2016, 08:35 PM   #2
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What track? Maybe buy some >91 octane gas for the weekend at the track?

Edit: I see you're going to T-hill. If it's in two days just spare yourself some headache and buy high octane there. Their 91 is mega expensive anyway if you can't drive to town.
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Old 09-22-2016, 08:37 PM   #3
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The easy answer is to just throw a 1:1 mix of 100 and 91 in the tank at the track. That'll get you 95-ish, you could do 1:2 to get closer to 93 if you wanted to save a little money, but 1:1 is safer. That's what I'd do for the short term.

For the longer term you'll want to retune it.

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Old 09-23-2016, 04:31 AM   #4
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Are you getting det with the 91? You might end up being ok depending on how close you were tuned on the 93.
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