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Location:
North Sydney
Registered:
May 2002
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Re: Tuning day
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Wed, 28 May 2003 06:08
 
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I hope I don't sound condescending in my explanations guys, just trying to explain without giving every finite detail.
There's two main aspects of fuel. Octane and density.
Think of them both separatly.
Density- If you have an engine with a fixed full load timing of say 20deg adv on normal unleaded. You then put Optimax in, it will produce more power because it is more dense. If its more dense it therefore contains more power per ml, pushing the piston down harder.
That's why you will get a gain in power without adjusting the timing.(It's only small though)
Octane- Its basically its resistance to ignition, whether it be from detonation or from the spark plug. You put in normal fuel again and on full load(say 10psi) your ECU will look up it's pre-determined ignition values that were determined at the factory by the engineers. They tune deliberatly on basically lowest common grade fuel you can get at the pump so the engine performs well and doesn't detonate on full load otherwise they'd have engine's being destroyed all over the place.
(This is where aftermarket ECU's rock cause you set all these values) Like Draven's 1jz pulling 183Rwkw on stock boost.
Now, in closed loop(light throttle, <3500rpm, highway conditions) the knock sensors are used and the ignition is continually advanced to detonation point and dropped back again. In closed loop therefore you will get more power.
Hope this answers it Frankie, 
[Updated on: Wed, 28 May 2003 06:11]
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