09-03-2009, 06:17 PM
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#20 (permalink)
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Base Member
Join Date: Aug 2009
Location: San Diego
Posts: 54
Drives: 09 Nissan 370Z PG M6
Rep Power: 17
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Quote:
Originally Posted by wstar
The big question mark with our cars is: given a stock ECU, is the stock ECU smart enough to tune itself upwards for a higher octane fuel automatically? We already know that the stock ECU knows how to de-tune itself when presented with lower-octane fuel by using sensors to detect the onset of knocking and making the appropriate adjustments.
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It's my understanding that it "tunes" itself using the knock sensor. There is no octane sensor. When it detects the onset of knock using the knock sensor the ECU throttles back thereby reducing performance. If there is no knock when running 91 octane and definitely no knock when running 101 octane, the ECU would never know the difference and run the same. It doesn't open up the throttle any more or provide more power. It just knows there is no knock happening. And the energy content of the gasoline does not go up with octane. 91 octane fuel has ~32MJ/liter of energy, 101 octane fuel has ~32MJ/liter of energy, 121 octane fuel has ~32MJ/liter of energy so the power of the engine is the same. The higher octane will allow you to run a modified engine with a higher compression ratio to get more power though.
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