Computers only compensate.
Certain engines are DESIGNED for a certain octane fuel. This completely supercedes ANY computer compensation. When a manufacturer specifies a MINIMUM octane rating, that reflects their engine design. Taking into account compression ratio, head design and flow characteristics -- along with many other factors -- and you REQUIRE a certain octane level. PERIOD.
And let's review what the Magliozzi brothers so well described:
Tom: Here's why. The lower the octane, the lower the temperature at which the gasoline explodes in the cylinders. And in certain "high compression" engines like yours, 87 octane gasoline explodes too early. Those early explosions are known as "pinging" and they eventually cause engine damage.
Ray: Premium gas (probably 91 or 92 octane, whatever is specified in your owner's manual) explodes when it's supposed to in your engine, and that's why the manufacturer of your car requires it.
Tom: In general, you should always follow the manufacturer's recommendation when it comes to octane. Using a lower octane can harm the engine over time, and using a higher than called- for octane is a complete waste of money.
Ray: And I guess that's the good news we can give you, Norma. You don't have to waste your money springing for 94 octane. You can stick with the nice, cheap, 92 octane stuff.
The bottom line: You can personally
choose whatever grade, blend or anything else you want to dump into your gas tank. Hey, urinate in there if you think it has some mystical quality. And it's true, you may not notice any driveability issues. But if your engine is designed for a minimum octane specification, then ultimately -- whether you want to admit it or not -- you are damaging the engine. Period. End of story.
And while you're free to use or abuse your car in any manner you deem fit -- after all, you paid for it -- to suggest that others should follow your lead is at best irresponsible and at worst ... well, you fill in the blank.
Please forgive the ranting tenor of this post, but every time fuel prices jump there are always these discussions by people looking to save a few bucks. Face it: you bought a premium mark. If you want to ignore the recommendations of those who designed, engineered and built the thing, hey, there's also no reason ever to change the oil, filter, brake fluid, anti-freeze or anything else, either. Think of all the money you'll save!
But if that is your philosophy, why don't you do yourself and others a favor: sell your Benz before you do damage to it and just buy a Ford, Toyota or some other brand that you can dump 85 or 87 octane in without having to justify, rationalize or BS others about your mistreatment of your once-fine automobile?
Take care and enjoy the ride,