Do I HAVE to use 91 octane in my car?

Yes, sorry. Per Autochannel News:

Fuel Requirement 91 octane unleaded premium gasoline

My gf has a 2002 Thunderbird which requires 91 octane gas. She’s only used 86 octane gas. It has 100,000 miles on it, and she’s never had an engine problem. Not ever.

My 350GT with a high mileage (180K) 5L w/some high performance gear runs a lot better on higher octane. Mechanic said I need to keep using it due to its milage. However have a friend with a M5 and uses lower octane and runs like a scalded ape.

I would be afraid as most people to put a lower octane in a high performance car.
Nobody wants to risk the damages it could cost.

@cardinal, I’m clueless. Is scalded ape good or bad? Seriously, I’d like to know what that means.

scald: verb 1: to burn with or as if with hot liquid or steam

Combine that with ape…no..no…

Right, so does a scalded ape run really fast, because it’s scalded and it’s trying to get away or does it run as if it is crippled?

Tell it like it is Cardinal.

Also, here’s your chance to add it to Urban Dictionary.

Actually, Cardinal compares it to a car performing well on higher octane, so I’d imagine in comparison, it’s bad.

Clearly lower octane won’t perform as well, but can it actually DAMAGE an engine? I have a friend who swears it can’t and as gas prices keep skyrocketing (like a scalded ape :P—best analogy EVER!) I would think more and more people will be doing this if there isn’t a risk of damage. Any mechanics/engineers who can give us the real-deal lowdown on this?

Answered my own question. The guys at cartalk have a short article on the subject. Basically, they say that it won’t hurt your engine as long as the car was made after about 1996 and you’re not putting any atypical stress on it (like driving up steep inclines, hot weather, or hauling weight). Day-to-day driving really won’t make any difference which is pretty cool.

In the end, even switching to a lower octane vs. a higher octane….the cost might be the same because i believe you will get better mileage from a higher octane gasoline in a high performance engine. Also you would notice performance benefits. Whats the sense of buying a high performance car, if it is not performing at its peak.

@patty that link pretty much says that the improvement in gas milage is very small between lower octane and premium. Also, most people would rather have the 30¢/gallon or so savings at the pump when they’re filling up for their daily gridlock commute where they’re really not going to feel the benefits. You can always put premium in for those times that you think you’ll notice the difference and don’t mind paying the extra cost.