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Old 08-12-2013, 09:01 AM   #1
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Race Gas or no?

I'm going to participate in a time attack hill climb that's coming to my town in a couple weekends. I am supercharged by VF engineering with a meth kit. I have access to C12 (118 octane) race fuel. Would i get any benefit out of running this over 93 pump fuel?

I believe the c12 is leaded though. Will that cause any problems? Do i need to be tuned to the 118 octane before i see any benefit or can i just run it and my ecu will adapt itself to it?

Thanks!
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Old 08-12-2013, 09:23 AM   #2
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I believe the stock ecu adapts up to 97 octane. I've ran 105 octane unleaded and it makes a big difference. You probably won't see any issues running leaded gas one time, if you use it consistently it will ruin your O2 sensors.
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Old 08-12-2013, 09:23 AM   #3
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You would DEFINITELY want to tune your car if you're going to run 118 octane. Reason being, the BMW ECU will "adapt" but only up to (I believe) 97 octane. I may be off on the exact number but that's the one that comes to mind.
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Old 08-12-2013, 10:02 AM   #4
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Wouldn't leaded fuel mess up the pump and filter?
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Old 08-12-2013, 10:30 AM   #5
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Cats (if you still have them) and O2 sensors will take the hit.
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Old 08-12-2013, 10:57 AM   #6
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i was worried about my o2 sensors and the leaded gas.

Does anyone know if the software and tune that VF does to the ecu allows the ecu to adapt to a higher octane then the 97 octane base limit?
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Old 08-12-2013, 11:40 AM   #7
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i was worried about my o2 sensors and the leaded gas.

Does anyone know if the software and tune that VF does to the ecu allows the ecu to adapt to a higher octane then the 97 octane base limit?
No it doesn't change. And what VF does probably shouldn't be called a tune.
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Old 08-12-2013, 12:21 PM   #8
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I would be worried about my cats, you could always get new o2 sensors somewhat cheap hell you could even throw in a fuel pump and filter, but cats are pretty expensive.
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Old 08-12-2013, 12:47 PM   #9
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OP, just run it the way it is.



Good luck at your event.
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Old 08-12-2013, 01:08 PM   #10
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OP, just run it the way it is.



Good luck at your event.
sounds good. Thats mainly what i was wondering, if it would be worth it to try out some higher octane or not. Looks like i'll just run my usual 93 and give it a whirl. I'm mainly doing it because its local and it should be fun.

Thanks for the answers guys
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Old 08-12-2013, 01:19 PM   #11
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higher octane will only add to detonation resistance. If you are tuned for 93 + meth, running higher octane will not benefit you at all. It's not worth the risk of running leaded IMO. Meth is a great setup BTW, depending on your dilution ratio and injection amount, your equivalent octane is likely in the 100+, on top of having cooler charge temps.
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Old 08-12-2013, 01:24 PM   #12
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If you are tuned for 93 + meth, running higher octane will not benefit you at all.
This is not true.
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Old 08-12-2013, 01:54 PM   #13
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This is not true.
Please explain. Unless the adaptability range of the ECU can scale beyond what was tuned for, you will see no benefit.

a 93 + meth tune is running AFR and timing targets set for that combination.

On a stock ECU, if it's adaptable to 97 octane what it's done is set its base timing table low with a dynamic advance table scaling up based on how happy or knock resistant the total advance timing is running.

A 93 + meth equivalent octane rating is allowing AFR to lean out significantly as well as run a considerable amount of total advance timing while being happy, so it likely would have maxed out the total advance option.

The tuner would have had to scale up the base timing so the 93 + meth was still not hitting the ceiling.

The only other advantage would be to run an oxygenated high octane fuel which even at the same AFR, timing and boost values produces more power, simply based on the nature of the fuel's combustibility.

FWIW: I tuned an STI of mine back in 05 for 91 + Meth and once added 108 octane leaded and took it to the track to compare and didn't run any better, in fact ran worse that evening. My tune was at the ceiling with 91 + meth....I was leaned out to 13:1 and running so much timing I simply stopped making power. At the boost level I was running, I couldn't make any more power with race gas because it wasn't making more power with timing and I wasn't comfortable going leaner.
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Old 08-12-2013, 02:16 PM   #14
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Because I would be willing to bet his car isn't tuned to utilize the methanol. I have close to the same setup and when I put 105 octane in my car it's like a whole new beast and pulls like a freight train. But I've been out of the game for a while, maybe VF is actually tuning cars now. Ha. Doubt that though.
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Old 08-12-2013, 02:25 PM   #15
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Because I would be willing to bet his car isn't tuned to utilize the methanol. I have close to the same setup and when I put 105 octane in my car it's like a whole new beast and pulls like a freight train. But I've been out of the game for a while, maybe VF is actually tuning cars now. Ha. Doubt that though.
Methanol effectively adds octane by slowing down the burn of the fuel and increasing knock resistance....

so if he's not tuned for methanol and can't adapt for increased knock resistance, why would higher octane benefit him, which is doing the same thing?

....?

I think you might be missing some key concepts on how to tune.
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Old 08-12-2013, 02:33 PM   #16
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I know jack s.hit about tuning. But I just told you, IT MAKES A DIFFERENCE WHEN YOU PUT 105 OCTANE IN THE CAR. I know it, I feel it. It's my car. Do you have this set up? I don't care what your knowledge is on tuning, really.
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Old 08-12-2013, 02:40 PM   #17
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I know jack s.hit about tuning. But I just told you, IT MAKES A DIFFERENCE WHEN YOU PUT 105 OCTANE IN THE CAR. I know it, I feel it. It's my car. Do you have this set up? I don't care what your knowledge is on tuning, really.
OK, so you're running methanol?

What octane fuel are you comparing? 93 vs. 105? If you're comparing 93 vs. 105, sure you might feel a difference because you are likely not at the ceiling at 93. Your timing can advance further when using 105. It's possible your 93 tune (or whatever it's at) is not particularly happy....so add 105 and you're finally able to run fuel trims and timing advance that the tune was designed for.

The OP with Methanol is effectively running 100+ octane, all the time. If his car is not "unhappy" with the tune on methanol, adding more octane won't increase power unless as previously stated, the fuel itself has properties that increase combustibility like oxygenated fuel.

Are you doing a direct comparison here? You have to take in some factors before you make claims something is or is not true if you really don't know what you're talking about.
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Old 08-12-2013, 02:45 PM   #18
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I guess I'm making assumptions. So my mistake. I would say he is more than likely not running pure meth but a mixture. But yes. A very similar set up.
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Old 08-12-2013, 02:48 PM   #19
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I guess I'm making assumptions. So my mistake. I would say he is more than likely not running pure meth but a mixture. But yes. A very similar set up.
Water slows down fuel burn too, it just doesn't decrease charge temps as well as methanol so it doesn't make power as well as methanol does.

So you are, or are not running methanol and thus comparing your experience of 93 + meth going to 105 + meth or are you comparing 93 to 105, WITHOUT methanol? Because the two scenarios are not even remotely going to produce the same results, regardless of the rest of the build similarity.
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Old 08-12-2013, 02:49 PM   #20
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Yes I am running methanol. 50/50 mix. And yes 92+ meth to 105+meth makes a very noticeable difference.
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