Gasoline/octane information

How gasoline and its octane rating affect your engine.

What is octane? Simply put, octane rating is a measurement of how much resistance gasoline has to detonation.

When your engine is running, it gets very hot inside the engine.  There are also small flakes of carbon left inside the cylinders after detonation.  These carbon flake build up and coat some frictionless parts, such as piston heads and lower valve stems.

Besides the heat, inside each cylinder just before the spark plug fires and ignites the gasoline & air mixture, the piston is traveling on its way up and creating great amounts of pressure. If the pressure increases enough, the gasoline will ignite without a spark.  High performance engines build up greater pressures than regular passenger vehicles.

So, gasoline manufacturers put additives into the gasoline to keep it from igniting too soon.  If the gasoline does ignite too soon, it creates a knocking sound. This knocking sound is probably telling you that you need to run a premium gasoline or you may ruin your engine. Here is why.

Your spark is controlled by the distributor.  Your distributor is the device that times your spark and tell s the spark plug when to fire.  Generally a distributor tells the plug to fire while the piston is traveling on its way up and the cylinder is creating pressure.  But the piston is traveling too fast so by the time the plug fires, the piston has reached the top of its upward travel and is just starting down as the spark ignites the gasoline/air mixture. The energy from the burning fuel (not an explosion) drives the piston down.

If the fuel pre-ignites from either the pressure I talked about in a previous paragraph, or because of a glowing piece of carbon left over from previous firings, you have pre-detonation. Pre-detonation is when the gasoline ignites way too soon while the piston is traveling on its way up and creates a knocking sound as the upward traveling piston has to overcome the energy of the burning gases that want to push the piston down against the momentum already in play.

At any rate, modern engines do not use distributors any more, they use computers.  These computers have a knock sensor in them and if they detect engine knocking, they retard the timing and save your engine from its damaging effects.  however, this action also robs some of the engines power and reduces the engines efficiency.  For example a truck that should be using high octane gasoline may not have enough power to haul a heavy load up some steep hills.  Or your Mustang or Cobra may not have enough power to trash that Chevy boy or Dodge hick (heaven forbid that should happen).

Running a premium high octane gasoline in an engine that does not need it does not help nor does it hinder engine performance. What does help is if you run a good quality gasoline that has additives to help clean your engine.

Along with good gasoline is good oil and regularly scheduled changes and engine filter changes.

Happy motoring.