100 Octane

[Flavor 987S]

Originally Posted by Ciao

What does that parameter (1-2 ppm of lead) indicate? Avg? Normal? Abnormal?

Should be "0".

Running race gas, even unleaded, will show trace amounts of lead, in your UOA.

[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?

[Ciao]

Originally Posted by Flavor 987S

Should be "0".

Running race gas, even unleaded, will show trace amounts of lead, in your UOA.

Zero (0) is impossible. Despite the belief that unleaded contains no lead, there is an unknown government regulation allows unleaded gas to contain lead to be added intentionally to gasoline, but does permit unleaded gasoline for motor vehicles to contain up to .05 grams of lead per gallon.

[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.

[Flavor 987S]

Originally Posted by Ciao

Zero (0) is impossible. Despite the belief that unleaded contains no lead, there is an unknown government regulation allows unleaded gas to contain lead to be added intentionally to gasoline, but does permit unleaded gasoline for motor vehicles to contain up to .05 grams of lead per gallon.

Your UOA should be zero. That's what I am talking about about, not the level of lead in your unleaded fuel. If you use race gas, your UOA will show 1-2 ppm, or higher, depending how much/often you run the race gas.

[azlvr]

So again, The octane # is it's resistance to detonation. So unless vehicle is setup correctly it won't help. #Oxygenated fuel will help. Unless you’ve increased your compression ratio which causes pinging or changed the timing which causes pinging, higher octane won’t help.

[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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[Ciao]

Originally Posted by maytag

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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Sounds good, so when high octane is not used and ignition is advanced (tuned) will detonation (pinging) occur?

[Quadcammer]

Originally Posted by Ciao

Sounds good, so when high octane is not used and ignition is advanced (tuned) will detonation (pinging) occur?

Yes but you have knock sensors that will retard the timing

[maytag]

Originally Posted by Ciao

Sounds good, so when high octane is not used and ignition is advanced (tuned) will detonation (pinging) occur?

Ciao, that's an oversimplification, but in the strictest sense; yes.

In the old days of distributor-ignitions, without knock sensors, etc, it was very common on "tuned" cars with high compression-ratios (or forced induction) to have an ignition curve that was so aggressive that detonation would occur. This was particularly true when the engine was warm, as that lowered the amount of compression before spontaneous combustion (and subsequent detonation) would occur. We did that because we were trying to get the cylinder pressures as high as we could, so we needed to have as much burn-time as possible. Higher octane would allow us to run a more aggressive ignition curve (which, believe it or not, we'd tune with springs and weights!!)

Now though, in today's world of improved combustion-chambers, improved cylinder-fill, direct-injection, hotter-spark and all of the sensors helping to adjust the mixture, this isn't as important. Getting a complete burn, quickly, is not as difficult to accomplish as in days past.

In short: only a fully-built, race-prepped engine with an aggressive tune which includes ignition-curve mapping, and high CR will benefit from higher octane fuel. And that's why they sell it primarily at the racetrack. :-)


Now, as someone else mentioned; Oxygenated fuel is something entirely different! haha. I've got lots of experience with oxygenated fuel, but never in a computer-controlled environment, so I've no idea how an ECU responds to that. I'd love to hear from anyone who HAS tried it, hehe. There's nothing that brings back vivid memories of superbike racing like a whiff of oxygenated fuel..... :dance:

[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.