romus

All about octane
by Jim Kerr

An interesting product hit the market recently and I put it to use immediately. Pennzoil makes it, and it is called the "Month of Power Maximum Performance Octane Booster". Four small aluminum cylinders of chemical in one box are enough to treat 300 litres of gasoline and carries a suggested price of $14.99. Why did I find this product so interesting? Because I have an antique Thunderbird car that prefers to run on nothing but gasoline with a high octane rating. There are many other classic performance cars and quite a few modern ones too that can take advantage of boosts in gasoline octane.

So what is octane? It is a rating that tells you how much the fuel can be compressed before it spontaneously ignites. Look at the gas pumps and you will find the octane rating for each grade of gasoline. Typically, regular gasoline is around 87 octane while mid-grades are 89 octane. Premium fuel is often 91 octane although some filling stations such as Sunoco and Mohawk have higher octane fuel available.

Gas pumps may show two octane numbers: RON and MON. The Research Octane Number, or RON, is measured under fairly easy test conditions. The Motor Octane Number, or MON, is a tougher test measured at higher engine speed and temperature. The average of these two values: Road Octane Number = (RON + MON)/2 and that is the number we commonly see at the pumps.

How do they measure octane rating of a fuel? Start with a $250,000 (U.S.) ASTM-CFR test engine from Waukesha Motors. This single cylinder engine has a moveable cylinder head enabling scientists to vary the compression ratio between 4:1 to 18:1 while the engine is running. The engine is run on the fuel to be tested while varying the compression ratio until the fuel begins to knock. Then the engine is run on different percentages of heptane and iso-octane under identical conditions until the same knock occurs. The percentage of iso-octane in the mixture is the "octane rating" of the gasoline.

If the fuel you use in your car doesn't have a high enough octane rating, you may experience pre-ignition or detonation. Pre-ignition occurs when the fuel/air mixture in a cylinder ignites before the spark plug fires. It can be caused by hot spots in the cylinder, red hot carbon deposits or extreme overheating. Detonation occurs when the flame-front in a cylinder does not proceed smoothly across the combustion chamber. The fuel may ignite spontaneously due to high compression or other sources of ignition. Pinging and knock are symptoms of pre-ignition or detonation and either of these can break piston rings and pistons.

Many drivers still believe that the higher the octane rating of the gasoline, the greater the power and the better the performance their vehicle will have. This isn't true. If your engine runs without knocking or pinging on regular fuel, then you will have exactly the same power on premium fuel. The fuel required by your vehicle is shown in the owner's manual. Most vehicles need only regular gasoline but there are times when higher octane fuel is needed.

Cars built in the 60's and 70's had higher compression ratios. High compression causes fuel to self-ignite so higher octane fuel is required. Older engines may have carbon deposits that increase compression even more. Cooling systems are often corroded so engines tend to run hotter and ignition control was pretty basic. My old Thunderbird is typical of older cars. It would ping and knock even when premium gasoline was used. Adding the Pennzoil Octane Booster (it contains MMT, the additive already used in gasoline to boost octane) eliminated the pinging and knocking enabling me to reset the ignition timing back to specifications for better performance and economy.

Newer performance cars may benefit too. Knock sensors on computerized engine controls retard ignition timing when engine knock occurs. We don't even hear the knock but performance and economy drop. Drivers that want the best in performance from their high performance engines need fuel that will not ping under heavy load.

Adding the Month of Power Maximum Performance Octane Booster was simple. Pour in one of the small cylinders of chemical to a nearly empty tank and fill with fuel. If you hear pinging from your engine, a higher grade fuel may help. For ultimate performance engines, a little help with additives may give that extra edge

jimrockford

Very informative article. It does a good job of explaining why higher octane doesn't necessarily mean more power.

White SR5

There it is spelled out. Nicely written and not confusing either! One question: what does MMT stand for? I like to learn!

Zach