100 Octane
 

What can I expect in performance if I pump in 100 Octane (50%/50% 91 Oct) in high altitude (Mile high city in Denver)

http://986forum.com/forums/uploads02...1549495283.jpg
http://986forum.com/forums/uploads02...1549495311.jpg

Others may not agree, IMO a waste of money, unless you really need that extra 2 HP with a properly tuned car on the track... others may not agree.

Most of the performance gain you'll notice will come from the reduction of weight in your wallet.

Sent from my SM-G930T using Tapatalk

I'm thinking of running 60% 91 Octane and 40% 100 Octane to average 93 Octane which the manual states is the best Octane

Higher altitude you can never find the higher octane stuff like down low. But you don't need it, either. Air density is too low. Use 91. It's appropriate for your car at that altitude.

Sent from my SM-G930T using Tapatalk

Unless you reprogram the ECU for 100 octane maytag is spot on

The octane # is it's resistance to detonation. So unless vehicle is setup correctly it won't help. #Oxygenated fuel will help.

Waste of $$$ unless you get a new tune. YMMV.

Our low octan gas here is 95 but I honestly can tell the car runs better on the 98 not really power wise but just smoother. I usally put high octan every other tank full. But I dont necassarily beleive its a required. You need to spoil your baby sometimes :D

Not the same octane rating scale

Not sure where you're at, but you're probably looking at RON numbers. Not the same rating scale. (Unless you're regularly buying fuel at the racetrack).

From wikismedia:
"Another type of octane rating, called****Motor Octane Number****(MON), is determined at 900 rpm engine speed instead of the 600 rpm for RON.****MON testing uses a similar test engine to that used in RON testing, but with a preheated fuel mixture, higher engine speed, and variable****ignition timing****to further stress the fuel's knock resistance. Depending on the composition of the fuel, the MON of a modern pump gasoline will be about 8 to 12 octane lower than the RON"

RON is more common worldwide, but RON has been the US standard for a long time. (Though we're beginning to see RON listed at many US pumps)

Sent from my SM-G930T using Tapatalk

Here are 2 MAJOR problems with your idea/plan:

1) The 100 octane is not going to be very fresh. At a race track, yes, but NOT at your local corner gas station.

2) Unleaded race gas like this still has elevated levels of lead. If you don't beleive me, run a Blackstone UOA, and you'll see about 1-2 ppm on your next test result.

I live in Spain by gas on US installation pump states 95 Octane in town pump tates 98 Octane, but on the base they are required post us rating. Will look to see if it say RON though.

Actually (1) the pump is located near the Bandimere Race 1/4 mile race track. So, it is highly likely it is fresh. Though lead is used in racing fuels it is not used by itself, but mixed with Tetraethyl Lead. So in my example, mixing a small percentage of 100 with 91 to reach a 93 on rare occasions seems insignificant.

My understanding is any lead in the gas will kill the cats.

You will basically see no difference between 91 and 93 RON
The ECU will adjust for virtually any octane 93 and below

Good, it's fresh.

If you keep running this race gas, do a UOA. I'll bet you start seeing 1-2 ppm of lead. BTDT.

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

Regardless of the lead, what is the point? You have less oxygen at your altitude so you do not need 93.

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.

Sent from my SM-G930T using Tapatalk

Should be "0".

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

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?

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.

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.

Paul,
Thank you! This table is very helpful.

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.

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.

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

Sent from my SM-G930T using Tapatalk

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

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:

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!

:cheers: 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.