I've read many a threads of people bitchin back and forth about fuel and octane ratings. Never thought i'd see a long discussion on a trance forum. Not to say you guys are bitchin, i'm just sayin. And awesome job on that hella long post on page 6.

So i was wrong about the fuel actually burning slower? regular and premium should, in theory i guess, burn the same rate just the resistance to knock is increased? So im not sayin your wrong but i've seen plenty of dyno runs (on the web anyway) that actually lose power the higher octane they go from what is optimal for them. Any idea's on why that is? At least thats what i understood from the post.

Awesome post anyway.

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Originally posted by biznology ^^now thats a reliable answer| although in my POS upping the octane from 85 to 87 did increase fuel efficiency marginally(in a high altitude area), but beyond that no increase is seen...

I don't want to discredit your experiences but a higher altitude will actually require a lower octane rating to properly retard engine knock. in high altitude areas an engine requires less air due to the reduced density of the atmosphere. Reducing the density of the air will also reduce the actual compression in the cylinder. Lower compression will result in less engine knock.

I would guess that you are seeing better fuel efficiency due to high engine load. High altitude areas are typically "hilly". A hilly area will increase the load on the engine. At low load only part of the total power is produced because the manifold is operating at lower compression therefore less octane is required to control knock. The higher the load on the engine the higher the compression, the more octane is required to control auto ignition.

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Originally posted by 650Raddict I've read many a threads of people bitchin back and forth about fuel and octane ratings. Never thought i'd see a long discussion on a trance forum. Not to say you guys are bitchin, i'm just sayin. And awesome job on that hella long post on page 6. So i was wrong about the fuel actually burning slower? regular and premium should, in theory i guess, burn the same rate just the resistance to knock is increased? So im not sayin your wrong but i've seen plenty of dyno runs (on the web anyway) that actually lose power the higher octane they go from what is optimal for them. Any idea's on why that is? At least thats what i understood from the post. Awesome post anyway.

That is roughly how it works. Octane rating is a measure of detonation resistance. Fuels with higher octane ratings actually explode less easily. So in a way the fuel will burn slower. The problem that occurs when you run a fuel with a higher octane rating that the engine was designed for comes in the ignition control loop of the vehicle.

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Originally posted by Dr. Cfire I don't want to discredit your experiences but a higher altitude will actually require a lower octane rating to properly retard engine knock. in high altitude areas an engine requires less air due to the reduced density of the atmosphere. Reducing the density of the air will also reduce the actual compression in the cylinder. Lower compression will result in less engine knock. I would guess that you are seeing better fuel efficiency due to high engine load. High altitude areas are typically "hilly". A hilly area will increase the load on the engine. At low load only part of the total power is produced because the manifold is operating at lower compression therefore less octane is required to control knock. The higher the load on the engine the higher the compression, the more octane is required to control auto ignition.

well i wont argue with technicalities, its just my experience that having 87 in the corolla is better, esp for mountainous highway stuff. doesnt do too much in the city|

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