mundman

I do a 50/50 race mix of VP 101 and 91 on occasion.

orthojoe

Unless the ecu is programmed to recognize higher than 93 octane (it isn't) and advance timing as a result, there is zero benefit.

DrJupeman

Arguably a detriment, too, other than lighter wallet, no?

Archimedes

I'd just like to know where you're buying this from a service station in the Bay Area, assuming it's ethanol free. AFAIK, all those stations got cease and desist letters years ago. The only way I was able to get T4 for my motos was by signing a form that said I was using it for closed course racing, and some places wouldn't even accept that without a valid race license. If there's a station here in the SF Bay Area selling ethanol free race fuels to the general public, I know a bunch of people that would definitely be interested on the moto side. Please, do tell, where?

'Trust'

It's a pretty common misconception that increased octane fuel (especially anything 95+) will increase performance by itself. In short; factory engine mapping will have fuel and timing maps for a given range of octane of gasoline (typically from about 79 octane to 95 octane), they are only calibrated for that range, so when you add octane above that, sure the tune/map could handle more timing due to the additional resistance to burn (octane), however, since it's not programmed to give any more timing than it would at say, 95 octane, even though it could handle more at 100 octane, the command just isn't there to add it. So in short, it's useless unless you're tuned for it. The only untuned benefit of 100 octane would be an additional buffer to prevent pre-ignition on a hot track day or something, but a slightly colder plug would do the same thing.

His basic description pretty much nailed it. The only possible benefit you'd see is additional resistance against pre-ignition from a hot track day or something, or insurance against "bad gas".

DrJupeman

Understood on what could be the advantages, but I'd think there is actually a chance of lower performance when running 100 with an engine not designed for it.

'Trust'

I'd respectfully disagree. If you put 100 octane in your car, your car would utilize a 93 octane map, and it would perform as well as it would with true 93 in it. 100 octane gasoline does not require additional fuel flow or anything. You're just not using "7 octane" that's available. It is arguably better fuel. It's not like E85 where it needs 20-30% more fuel flow due to an increased burn rate. I don't think by the sounds of it you'll be running 100 octane anytime soon so I wouldn't worry about it.

DrJupeman

See earlier in the thread, I run 100 in my GT3 Cup and have always wondered why we all do.

The advantages offered by higher octane for a car designed to take advantage of it, should make it less efficient in a car designed for 93. 100 doesn't burn as easily as 93 when run as if it is 93. No "free lunch", I'm wagering.

'Trust'

"Should" doesn't mean "does". That seems like speculation to me. Degree of timing is related to the point at which the spark plug ignites and how close that is to the piston's top dead center (TDC). Where pre-ignition and octane become important is when you are commanding timing very closely with the TDC position of the piston during it's stroke, which in an ideal scenario for power output, you want it at the moment the piston meets TDC. However, lower octane fuel can ignite not just from the spark, but from the heat of the plug. A more aggressive timing strategy mean more heat that is retained in the plug between ignition or sparks. Higher octane fuel is less resistant to igniting from the heat of the plug alone, hence why octane is resistance to burn. I promise, when the plug actually sparks, they'll both ignite. 100 octane won't have a tougher time doing so, lol.

The reason you run 100 is because with those laps, and the higher average RPM you're holding ( = more aggressive timing), the plugs will hold more heat, which will eventually lead to pre-ignition if you don't have a good buffer of octane.

You seem rather set in your opinion, which is great. Just consider that another insight. I think I'm done.

Mike in CA

I believe 'Trust' is right. Once spark is applied to the air/fuel mixture it will ignite, regardless of the octane rating, and the energy released is identical, all else being equal with the formulation of the fuel. Higher octane does help prevent pre-ignition in high compression engines, however. From everything I've ever read, the only downside to using high octane fuel in an engine that doesn't require it is a financial one.

I buy Sunoco SS100 unleaded at Sonoma Raceway. It's also available from a local fuel distributor (Redwood Oil) in Santa Rosa in 5 gallon cans but it's cheaper and more convenient for me to go to the track and fill my own containers.

Sunoco 100 has a research octane rating of 104 and an octane rating (R+M)/2 of 100, but it's not ethanol free; it's 9.5% ethanol by volume. Like you, I don't know of any sources for ethanol free fuel in the Bay Area and would also be curious to know where it's available.

Karl911

I have a GIAC stage 2 + tune on my TTS.
GIAC give you an ECU programmer to switch between stock 93, tune 93, and race 100. +30 Hp in 100 Pctane tune.
Basically they retard the timing on 100 oct tune.
Apr does the same on my S8 Audi. +40HP
Both warn you not run 93 on race tune!
Running 100 in a car tuned for 91or 93 is Ok, but a waste of money.

Archimedes

Ah, I though it was ethanol free. When I quit moto track daying about two and a half years ago, you could still get T4 (Ethanol Free) directly from VP's distributor in Benicia. A while back you could also get it through a few local shops if you presented a race license and signed the requisite paperwork. About $12 a gallon back then IIRC. In addition to eating rubber hoses, ethanol gas was known to deform the gas tanks of some of the italian bikes (Ducatis, Aprilias), so it was good to have on hand to leave in your tank, rather than regular gas.

DrJupeman

I'm not sure how much this has to do with the "heat of the plug" but all to do with compression and the ability to advance timing. Higher octane is less likely to spontaneously combust from compression which means it is more resistant (not less). It is this that I'm getting at:

"The higher the octane rating of gasoline, the more detonation inhibitor compounds it contains. Most of these compounds have lower heat content - combustion energy - than the alkanes in the fuel they displace. So, in most cases, the higher the octane, the lower the combustion energy. Not only are you wasting money buying higher octane fuel, in most cases you'll be getting marginally inferior performance too."

Mike in CA

That's interesting and something I'd not heard before. Can you link to your source? Thanks.

Zeus

I've seen many discussions on this topic, but I have always wondered if these higher octane/specialty/racing fuels are actually better in quality than anything you will find at your local service station.

I have had on two occasions in the past been hit with "bad" pump gas from a gas station. Both water and other contaminants along with possibly the age of the fuel was the culprit. The theory being that most people buy the "cheap stuff" 87 octane and very few pump premium 91-93 into their cars. Thus the premium fuels sit in the tanks of gas stations for far longer than the regular fuels.

Some people tend to want to put the best possible motor oil into their pride & joy, so I wonder why there isn't a market/business case, or car enthusiasts just entertaining the thought of a better overall quality of fuel for their street/track car than your ordinary pump gas.

Hmm...

I've actually thought of this business idea before, but I thought Audi was working on a Bio-Fuel "gasoline" as an alternative fuel to pump gas. But I guess if it burns, it creates CO2...and thus will still be a problem in the future. Too bad a manufacturer such as Porsche has never developed a "better" fuel available through their dealerships. Show me the money.