87 vs 93 octane tune....... - Mustang Evolution

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Old 11-12-2009, 05:02 PM   #1
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87 vs 93 octane tune.......

Ok, so I don't have one of the fancy, new tuners, just and old superchips tuner. The only tune options it gives me, is 87 or 93, and factory fan cut-on or superchips fan cut-on. When I got the car, it was tuned for 93, but had been running 87. I tuned it back to 87, to see if I could pickup a few mpg's, but I can tell it's nothing noticable! Should I leave it as is? What would be the pros/cons of tuning back to 93, and still running 87?
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Old 11-12-2009, 07:38 PM   #2
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Re: 87 vs 93 octane tune.......

Tuning for 93 octane and then running 87 octane will negate the performance enhancements of the 93 tune. I'm sure that the 93 tune changes your air/fuel ratio somewhat, as well as the timing curve, to take advantage of the increased spark knock protection of the premium fuel. Making those changes and then running regular doesn't allow your motor to reap the benefits of the changes. If you change it back to the 93 octane tune, be sure to have a full tank of the good stuff first, and then run 3 or 4 tanks of premium through it to let everything adjust. Then you should be able to tell the differences in the tunes.
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Old 11-12-2009, 07:51 PM   #3
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Re: 87 vs 93 octane tune.......

AHHH.....10-4! That's what I was wanting to know. I'll just keep the 87 tune for now, cause I HATE to pay that damned much for gas!!!
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Old 11-13-2009, 06:28 AM   #4
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Re: 87 vs 93 octane tune.......

My ProCal tune is a 91 octane tune, allowing me to go anywhere in the USA without worrying about finding 93 gas, especially out west. Anyway, with my 16-gallon tank, I try to refill when it gets to half full, so 8-10 gallons of premium costs at most $3 more than regular.
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Old 11-13-2009, 09:00 AM   #5
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Re: 87 vs 93 octane tune.......

It will add some timing/fuel but I never noticed a Seat-of-the-Pants difference

I did end up having to go back to the 87 tune as my car would ping below 2k RPMs under any sort of load using the 91 tune, even if I adjusted spark/fuel below those points

Maybe I need to run some seafoam
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Old 11-13-2009, 09:07 AM   #6
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Re: 87 vs 93 octane tune.......

Speaking of 93 gas, in our area we have 93 as our top gas. Why is it in other parts of the country do they have only 91 as the top gas? I have thought about changing my tune to 93 since that is all I use.
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Old 11-13-2009, 09:30 AM   #7
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Re: 87 vs 93 octane tune.......

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It will add some timing/fuel but I never noticed a Seat-of-the-Pants difference

I did end up having to go back to the 87 tune as my car would ping below 2k RPMs under any sort of load using the 91 tune, even if I adjusted spark/fuel below those points

Maybe I need to run some seafoam
hmm.....when I had the 93 tune with 87 gas, you could hear a crazy noise when at WOT.....I'm assuming it was the vavles rattling? Since I've tuned it back to 87, it's not doing it. I'm assuming it had something to do with the timeing/spark?
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Old 11-13-2009, 09:44 AM   #8
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Re: 87 vs 93 octane tune.......

Um, no, that was detonation aka knocking, pinging. That is bad bad bad stuff for your engine....which is why you don't run gas lower than your tune octane rating.

It had everything to do with the timing...it had too much advance for the octane and the gas was igniting before the plug fired. You're lucky it didn't do a lot of damage if you ran it this way for a while.
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Old 11-13-2009, 11:27 AM   #9
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Re: 87 vs 93 octane tune.......

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Um, no, that was detonation aka knocking, pinging. That is bad bad bad stuff for your engine....which is why you don't run gas lower than your tune octane rating.

It had everything to do with the timing...it had too much advance for the octane and the gas was igniting before the plug fired. You're lucky it didn't do a lot of damage if you ran it this way for a while.
That's what I needed to know! I'd had it less than a week when I tuned it to 87. And I don't think it'd been driven much in the past year before then.
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Old 11-13-2009, 03:16 PM   #10
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Re: 87 vs 93 octane tune.......

rickf73, octane is lower out west due to the thinner air at the higher elevations out that way. When I lived in Utah while working for the Air Force, the elevation in the Salt Lake valley was roughly 4800 ft, with close to 10k foot mountain peaks close by. The thin air doesn't need as much fuel, nor as high an octane rating, to burn properly.
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Old 11-13-2009, 05:00 PM   #11
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Re: 87 vs 93 octane tune.......

Um, why does colorado have 93 octane?

And Rick, I believe your tune is already 93 only...at least I would expect it should be in a supercharged application like it was in the 03/04 cobras.

The difference in octane is more related to emissions than it is the amount of octane needed to burn. You'd have to read up on why different states, like commifornia, have limited themselves to 91 as the max. I'm sure it is some entertaining reasoning.
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Old 11-13-2009, 06:18 PM   #12
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Re: 87 vs 93 octane tune.......

As far as i read it is set at 91 now.
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Old 11-16-2009, 08:52 PM   #13
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Re: 87 vs 93 octane tune.......

Sorry for the mistake about Colorado. Never lived there, nor do I want to. When I first arrived in Utah, I asked the local Chevy dealer if it was okay to burn 85 octane unleaded in my '03 S-10, which the owners manual said needed 87 octane. The tech I asked said that the octane ratings were lower due to the altitude, and that it wasn't necessary to retune the computer since spark knock (detonation) would not occur. Guess it depends on who you ask.
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