Running race gas
06-03-2010, 10:21 AM
#6
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It burns slower, you are not getting the optimum combustion of the fuel if you're not tuned for it. Slower burn means it takes longer for the potential energy to be released, reducing the amount of peak kinetic energy produced instead you're just prolonging the burn time. Same amount of kinetic energy produced, just over longer period of time.
Edit:this is not exactly correct but something along these lines. It's an easy way of thinking of it
Edit:this is not exactly correct but something along these lines. It's an easy way of thinking of it
06-03-2010, 10:35 AM
#7
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That is what I found also but I blend in 100 or 104 with our crappy 91 oct out here and bump it up to about 93-95 but using straight 100 or higher doesn't gain anything w/o being tuned for it a lot of the evos/sti's have two tunes and load a 100 oct or e85 tune up for track days. As does the gm stage 3 tune has the high octane mode for 100.
Gas blend calculator
http://ranney.com/mjr/fuel_blend.html
Gas blend calculator
http://ranney.com/mjr/fuel_blend.html
06-03-2010, 12:21 PM
#8
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Call me stupid. On second thought call me uninformed/misinformed on the octane discussion. There are some people here that seem to actually know something about octane. Our ECM corrects ign. timing to compensate/protect for lower than recommended octane levels, by way of the knock sensors. Correct? Is there a programmed ign advance limit in the ECM that prevents the timing from going beyond a certain point in ANY event? If so what is that point? And could that point be removed, or adjusted, to continue advancing the ign timing depending on available octane/knock?
Like I said. I'm not the sharpest tool in the shed. Just sharp enough to get the ax stuck 1/2 way through the log.
Like I said. I'm not the sharpest tool in the shed. Just sharp enough to get the ax stuck 1/2 way through the log.
06-03-2010, 12:26 PM
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i am tuned for 100 octane cause of meth, when i go into boost with my meth kit off running cam 2 110 octane it's slower and runs like ****. if you tune a few degrees less than the octane calls for just to be safe, it'll get you tons of free hp. just keep in mind most race gas contains lead and will beat up your o2 sensors and almost immediately wreck your cat.
06-03-2010, 12:30 PM
#10
Call me stupid. On second thought call me uninformed/misinformed on the octane discussion. There are some people here that seem to actually know something about octane. Our ECM corrects ign. timing to compensate/protect for lower than recommended octane levels, by way of the knock sensors. Correct? Is there a programmed ign advance limit in the ECM that prevents the timing from going beyond a certain point in ANY event? If so what is that point? And could that point be removed, or adjusted, to continue advancing the ign timing depending on available octane/knock?
Like I said. I'm not the sharpest tool in the shed. Just sharp enough to get the ax stuck 1/2 way through the log.
Like I said. I'm not the sharpest tool in the shed. Just sharp enough to get the ax stuck 1/2 way through the log.
06-03-2010, 12:42 PM
#11
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how your ECM is set-up is that it has a "High Octane spark table" and a "Low Octane spark table" it normally runs on your high octane table which has a set amount of ignition timing. if your car knocks for a significant amount of time, it will revert back to the low octane table which has less ignition timing. the only way to advance your ignition timing would be through a tune
06-03-2010, 06:57 PM
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It burns slower, you are not getting the optimum combustion of the fuel if you're not tuned for it. Slower burn means it takes longer for the potential energy to be released, reducing the amount of peak kinetic energy produced instead you're just prolonging the burn time. Same amount of kinetic energy produced, just over longer period of time.
Edit:this is not exactly correct but something along these lines. It's an easy way of thinking of it
Edit:this is not exactly correct but something along these lines. It's an easy way of thinking of it
That makes sense, thanks guys.
06-30-2010, 05:17 PM
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So, with all this being said... Say you were to put more than you wanted of 100 Oct mixed with your 91 Oct, ran your car with no cooling mods in 90-100 deg track weather, and increased your elevation by 1500+/- feet, would you loose about 3-4 MPH in your trap speed un-tuned?
Cause that's what probably happened to me...
Cause that's what probably happened to me...
06-30-2010, 05:30 PM
#21
So you're saying there are TWO seperate tables with TWO preset advance limits and the knock sensors toggle between the two? I would have thought the advance would be a variable dictated by knock but with a fixed limit. Very interesting. Thanks for helping me sort this out.
It knocks a lot. They basically cranked up the timing advance and are depending on the ECU to detect and retard the timing back down as needed.
It says something about GM's tuning demeanor, but also says something about how far ECUs have come since GM's willing to back that strategy with a warranty.
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