C10 VP Race Fuel. $60+/5 gallon can. Ran it on my (then) 998 biposto. Iridium spark plugs, 60.5mm termi full system. Otherwise stock engine (with nichols flywheel) & stock ECU. - Ran beautifully...
It ran less well on 91 or 93 and even worse on 89 once when I had no other choice. That was nightmarish... it sounded like it was dying.
Generally speaking, the WORST thing that a non-oxygenated, unleaded higher octane fuel will do is foul your plugs. There are some other aspects which need to be considered (read:
CONSULT THE MANUFACTURER BEFORE USING THE SPECIALIZED FUEL IN YOUR DUC AS I DID), but for the most part, that's it. The BEST it will do is add power -
all throughout the rev range and protect your engine from thermal detonation - caused by pre-ignition of the air/fuel mixture.
www.vpfuels.com
C10
The best non-oxygenated unleaded racing gasoline available. It meets ASTM D-439 standard specifications for automotive gasoline and is street-legal in most states. C10 does not contain any metal compounds and will not harm catalytic converters or oxygen sensors. Used by national champions in SCCA and IMSA stock classes.
• Color: Clear
• Motor Octane: 96
• Research Octane: 104
• R+M/2: 100
Here is some info from their site:
http://www.vpracingfuels.com/vp_01_fuels.html#
FOUR FUEL PROPERTIES
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Listed below are the four basic qualities of fuels. As in everything, there are trade-offs. You can't make a racing fuel that has the best of everything, but you can produce one that will give your engine the most power. This is why VP produces different fuels for different applications. The key to getting the best racing gasoline is not necessarily buying the fuel with the highest octane, but getting one that is best suited for your engine.
1. OCTANE: This does nothing more than rate a fuel's ability to resist detonation and/or preignition. Octane is rated in Research Octane Numbers, (RON); Motor Octane Numbers, (MON); and Pump Octane Numbers (R+M/2). Pump Octane Numbers are what you see on the yellow decal at gas stations, representing the average of the fuel's MON and RON. VP uses MON because this test method more accurately simulates racing conditions. The conditions under which fuels are tested using the RON method are not as demanding, thus the number is normally higher than the MON rating. This leads many other fuel companies to rate their fuels using the RON in an effort to make them appear more resistant to detonation. Don't be fooled by high RON numbers or an average -- MONs are the most relevant ratings for a racing application. Be aware, however, the ability of fuel to resist detonation is a function of more than just octane.
2. BURNING SPEED: This is the speed at which fuel releases its energy. At high RPMs, there is very little time (real time - not crank rotation) for fuel to release its energy. Peak cylinder pressure should occur around 20° ATDC. If the fuel is still burning after this, it is not contributing to peak cylinder pressure (which is what the rear wheels see).
3. ENERGY VALUE: An expression of the potential energy in the fuel. The energy value is measured in BTUs per pound, not per gallon. The difference is important. The air:fuel ratio is expressed in weight, not volume. Generally speaking, VP's fuels measure high BTUs per pound and thus, have a higher energy value. This higher energy value will have a positive impact on horsepower at any compression ratio or engine speed.
4. COOLING EFFECT: The cooling effect on fuel is related to the heat of vaporization. The higher a fuel's heat of vaporization, the better its ability to cool the intake mixture. A better cooling effect can generate some horsepower gains in 4-stroke engines, and even bigger gains in 2-stroke engines.
