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post #1 of 6 (permalink) Old 03-28-2005, 05:28 PM Thread Starter
 
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fuel

Anybody try running a tank of 100 Octane?,,,station near me has it ,,,buddy says to try or mix it up with 94,,,what say the crowd?
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post #2 of 6 (permalink) Old 03-29-2005, 08:24 AM
 
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Originally Posted by badtmpdgoat
Anybody try running a tank of 100 Octane?,,,station near me has it ,,,buddy says to try or mix it up with 94,,,what say the crowd?
Waste of money...

I run 100 or 104 unleaded race fuel in my stock Z06 in SCCA T1, but... my PCM has been reprogrammed with advanced timing and modified A/F mixtures.

I've read that a higher octane fuel has no more energy than a low octane fuel, it just has a different burn rate that makes it less susceptable to early detonation (e.g. knock or pinging). Early detonation is very bad for a motor and the LSx motors have knock sensors in the valley under the intake. As these sensors detect the inception of knock, they send a signal to the PCM to pull timing which reduces power in a big way.

So, unless your PCM is modified to run more advanced timing to take advantage of the fuels resistance to early detonation, you won't see any appreciable difference from 100 octane fuel. But... if the conditions are such that the car is on the verge of knock, a higher octane fuel will help prevent knock and thus the PCM won't pull timing. So, using a higher octane fuel on a stock PCM may prevent loss of HP, but won't gain you HP.

As a related note, be very careful about most Octane Boosters (including AMSOILs). Almost all of them have lead in them which is very very bad for the 02 sensors. If you are thinking about using an Octane Booster for the track (to prevent knock and pulling timing), read the bottle very closely.
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post #3 of 6 (permalink) Old 03-29-2005, 10:20 AM
 
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Agreed. Don't need it.
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post #4 of 6 (permalink) Old 03-29-2005, 12:26 PM
 
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not true the cars computer is always advancing and retarding the timing using 100 -or 104 octane will allow the computer to advance the timing more thus giving you more power i run race fuel in my gn at the track and is like a whole new car thats not to say that the price of a gallon of 100 octane vers. the power increase from using it is most likely not worth it but it would be cse once in a while cool to use once in a while def. if you go to the track.
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post #5 of 6 (permalink) Old 03-29-2005, 08:59 PM
 
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Unless the calibration in the car's ECU has been programmed to take advantage of the higher octane fuel through more spark advance YOU ARE WASTING YOUR MONEY. Generally even on HiPo cars with higher compression the most OEs cal for is 91 octane (yes, not even 93), which then takes out spark depending on knock sensors detecting you know what (just trust a big-3 powertrain guy on this one people).

That said though, if you are runnning forced induction and are playing with boost it's a totally different matter, because your dynamic compression ratio will rize with added boost.
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post #6 of 6 (permalink) Old 03-30-2005, 08:21 AM
 
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Quote:
Originally Posted by GNX231
not true the cars computer is always advancing and retarding the timing using 100 -or 104 octane will allow the computer to advance the timing more thus giving you more power...
That is only true to the extent that the timing can be advanced to the levels specified in the tables in the PCM. The stock tables only go so far. Changing these tables is how tuners like Hypertech can get more power out of a car.
As I mentioned above, my PCM was reprogrammed to adjust the values in these tables to much more advanced timing knowing that knock wouldn't be as much of a problem with the higher octane fuel.
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