100 Octane

[maytag]

Originally Posted by Ciao

We do not have less oxygen; we can breathe, we have reduced air pressure.

Which results in less oxygen, by volume, in the cylinder. ;-)

You're both right. But ultimately it's the cylinder pressure which, as it increases, requires a higher octane (resistance to detonation). Thus: lower air density=less cylinder-fill=lower cylinder pressures = lower octane requirement.

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[Ciao]

Originally Posted by maytag

Which results in less oxygen, by volume, in the cylinder. ;-)

You're both right. But ultimately it's the cylinder pressure which, as it increases, requires a higher octane (resistance to detonation). Thus: lower air density=less cylinder-fill=lower cylinder pressures = lower octane requirement.

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Great explanation Maytag. Does that mean even if the P car was tuned (chipped) for 93+ Octane, at higher altitude the increased Octane would not make a difference?

[maytag]

Originally Posted by Ciao

Great explanation Maytag. Does that mean even if the P car was tuned (chipped) for 93+ Octane, at higher altitude the increased Octane would not make a difference?

The only way your "tune" benefits from higher octane is if it advances ignition timing to the point of detonation ("pinging")

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[Paul]

Octane comparison here:

Octane rating conversions - PencilGeek's BMW Blog

[Cunningr]

Originally Posted by Paul

Octane comparison here:

Octane rating conversions - PencilGeek's BMW Blog

This is very good post I am going to check our gas stations rating, i always thought it was in US rating, but now thinking i might be wrong.

[Ciao]

Originally Posted by Paul

Octane comparison here:

Octane rating conversions - PencilGeek's BMW Blog

Paul,
Thank you! This table is very helpful.

[Racer Boy]

Real race gas does have a formulation that makes more power than regular gas that you buy at a retail gas station. When I raced a Spec Miata, dyno tests showed that race gas was worth about 1.5 HP. Not a lot, but every little bit matters when you are in a spec class. Would one notice 1.5 or 2 HP in our cars? Probably not, unless you were on the track next to an identical car that wasn't using race gas. You would pull them a few inches down the straight!

The fumes from race gas are one of those smells that instantly takes me to the race track. Its a smell one never forgets!

[Ciao]

Originally Posted by Racer Boy

Real race gas does have a formulation that makes more power than regular gas that you buy at a retail gas station. When I raced a Spec Miata, dyno tests showed that race gas was worth about 1.5 HP. Not a lot, but every little bit matters when you are in a spec class. Would one notice 1.5 or 2 HP in our cars? Probably not, unless you were on the track next to an identical car that wasn't using race gas. You would pull them a few inches down the straight!

The fumes from race gas are one of those smells that instantly takes me to the race track. Its a smell one never forgets!

I notice a difference in my 'turboed' Audi and am going to try mixing 91 and 100 to obtain a 93-94 rating in the Boxster.