low octane gas

[alanc]

I've always used premium gas for my 500SL (1983), but as an experiment, I've gone a couple of tanks on regular gas. I don't notice a bit of difference--no pinging, still starts instantly, same power, same perfect idle. All of this kind of surprised me, because I've heard the Euros have a little higher compression than the others. I haven't checked mileage, but I doubt there's much change there either, based on comparisons I've done with other cars.

Is there any reason to spend the extra 15 or 20 cents a gallon if the car still runs the same? Does higher octane burn cleaner, or keep the injectors from clogging, or anything along those lines?

[jcantor]

In a word: NO.

As long as you are not hearing any pinging under hard acceleration, there is no reason to pump more money into the oil industry.

[G-Benz]

I don't believe the euro models had anything tweaked differently on their motors...except for ignition timing.

Domestic versions are retarded by a couple of degrees to protect the engine from the lower grades of gas available. Your ignition timing may have been adjusted at one time during service, otherwise, you would be pinging.

This is discussed in the "Performance Paddock" forum at length, since many have discovered they gain a performance enhancement cheaply simply by advancing the timing to euro specs...but then, you will have to go back to using higher-octane fuel.

[alanc]

What is pinging caused by? I know the fuel's not burning as completely, but what's making the sound?

[BlueBabyBenz]

In a gasoline engine, pinging, or pre-ignition, occurs when the combustion happens too early. Higher octane rated gasolines resist by requiring a higher combustion temperature. Various parts are receiving the pressure spike before they should. That's the source of the sounds.