The octane rating is the number given for the resistance of the gasoline
to ignite. The higher the rating, the harder it is for the gasoline to burn.
Your engine may knock if you are using a lower octane rating than is
recommended by the manufacturer. Also, as an engine ages carbon tends to
build up within the combustion chamber to the point that it increases the
compression ratio. Therefore, older engines sometimes have a tendency to
knock when burning the recommended fuel octane. The reason for the knocking
is that the fuel/air mixture is igniting too EARLY. Engines are designed
(compression ratio/timing) for a specific octane rating - it is typically a
HUGE waste of money to use a higher than recommended octane rated fuel.
Therefore, the easiest answer to your question regarding the proper octane
fuel to use is to use the octane rating as close as possible to what the
manufacturer suggests for the engine. This mindset assumes you have not made
major modifications to the engine (compression ratio/timing).
Yet another $.02 worth from a proud owner of a 1970 Mach 1 351C (searches
for the highest octane I can find) @
"bg_jr." <firstname.lastname@example.org> wrote in message
> Might be a crazy question but . . . .
> I got my 1990 Grand Marquis 5.0 EFI when it had around 50,000 miles on it.
> Now there are 145,000.
> I knew the previous owner well and he told me that he had used high test
> gas from the day he bought the car so I continued the same.
> Now with the gas rip-off going on, one day I had put AMOCO Silver in
> instead of Gold and I might be nuts but to me the car seems to be running
> better. Idling, acceleration and more, they all seem better and I know
> car like the back of my hand.
> Is this in my mind or is it possible that a lower octane gas can make
> changes for the better in my car?
> Still scared to use regular though.