I'm aware of that refinery tidbit but perhaps others aren't. Local tuners know which brand is best for power and if one needs more volume for the same power. i.e. which additive package has the most knock resistance and energy. Ask, they will have an opinion. Locally, Texaco WAS preferred in 93. Texaco left the market and premium went from 93 to 91. Yep, the local refineries stopped making 93. Now 93 comes from another island, is carried by a few independents and is triple the price of 91. But when tested it comes in at over 94 octane. Anyone have an opinion on oxygenated fuels showing leaner AFR's at WOT? Off topic, gotta stop myself. I've put every brand of gas in some car sometime during my life. Correct octane, not enough and too much. Use what's recommended unless you've tuned your car for more is my position. I've never damaged an engine driving day to day with less than recommended octane but the marbles in the motor sound was menacing.

Les

 

Marbles in any motor isn't good no matter what fuel you use. Seriously, if you have a modern engine and there is a noise associated with using an octane rated gasoline 2 points below the required (by a manufacturer who might have some sort of an incentive to requiring a certain octane rating, ie Mobil1 oil required) then you have a problem associated with that particular motor above just the gasoline. Dirty gas, watered down gas, are just two examples (of a huge list) of actual problems but these are exceptions to a rule. Remember, I am not talking about modified engines or overhauled engines in engine bays, just your production run engines under a hood. Older carbureted engines with distributors, older motors dropped into modern cars and spliced in, or new motors not designed or completely installed with ALL the designed sensors installed correctly, all bets are off on those. I stand by 89 octane from a reputable station (remembering even they can get a bad load on occasion and no amount of octane in that gas will matter) for a car that a manufacturer requires 91 octane. Published specifications posted/designed for are why a specific octane rating is or may be a requirement for this or that auto engine. Engineers MUST build from a specification starting point. As a matter of my experiences and research to include articles published extensively (and no I have no numbers or copies to 'prove' this stated conclusion), modern engines with the level of sensors and computers equal to our 3.2L motor will not be harmed by using 89 octane if the 'required' octane rating is 91. Remember, they also say in these manuals that NO ADDITIVES are to be used yet you consistently see this person or that person dump this or that into their motors without hesitation. The bottom line IS the bottom line. If you want to spend the monies, or not, it is up to the one pulling out the money that ultimately makes his or her decision. You are not going to 'hurt' your motor by purchasing and using 89 octane. Heck, some even buy 93 octane, that is also the choice of the one pulling out the cash. I, in good faith, cannot tell someone 89 octane will hurt their motor if it doesn't. It is and always is a matter of choice based on the totality of the research I have done and I burn locally sold 89 octane. Economically speaking (and it is the ONLY consideration) it is just misinformation (IMHO) to be spending another $0.20 per gallon for 93 octane here, for our 3.2L motors. Peace out!

 

The OP is talking about using 87 octane in a car that calls for 91. My 300C pings with 87 octane at half throttle and higher. It's done it for 10 years every time I've put 87 in the tank. The manual calls for 89.

Les

 

I would suggest to you that there was and is something wrong with the car, or the gas station your getting that 87 octane from. It of course is a given there is no modifications done by either you or any prior owner or dealership, the engine is the 340-hp 5.7-liter V8, and that the car is at least a 2005 or newer. I see some problems reported with engine/fuel problems here ( 2005 Chrysler 300C Problems, Defects & Complaints but the quick research I just did is in no way a definitive result). By law, gas is randomly tested at various points throughout its distribution system for quality and water/contamination within. If your putting 87 in from many different stations geographically separated from each other over a period of time covering multiple sources, and your not 'beating' it all the time with WOT and highly aggressive accelerations, and from the beginning you have taken care of the basic oil/filter maintenance requirements (good mechanical condition), then it (in my opinion) is something out of kilter in the car your putting it in. Since it is that old of a car, it is way beyond any hope of having it fixed under any warranty unless they accept responsibility (unless it is UNDER some kind of documented recall or emissions warranty and they can duplicate your results which is HIGHLY unlikely). I doubt this can be fixed without you incurring a large fee.

 

Stock except Air Hammer intake. April 2004 build date. I suppose something could be wrong but don't think so. The PCM was flashed once by the dealer when I took it in under warranty complaining of rough shifting into reverse. I asked for the catalytic converters to be checked once. Checked out fine. Mostly maintained by moi. Since you seem sure something is up I'll investigate but I think some engines are more octane sensitive than others and nothing else. I've had the engine on a dyno for kicks and giggles in 2008 or 2009. No signs of detonation …. had 91 in the tank at the time. Runs great on a mix of 87 and 93 which is it's normal diet since 89 and 91 were taken off the local market.

Les

 

Interesting reading...or ranting...or both. Somewhat educational, too. My Audis also call for 91 octane. Yes, the computer can adjust for lower octane but it does affect performance while not seeming to impact gas mileage. I either fill them with premium 91 or 93, depending on what is available, or I alternate 1/2 tanks of mid-range and premium. I've been doing this on an A6 with 235k miles and she's still driving strong although the body is starting to go, but that's not due to octane. I do NOT use regular, 87 octane ever.

 

I use 93. Im not screwing my car up am I? Just got it.

 

NO!!!!!! If you had read the complete discussion you would already know the answer.

 

Good I knew it took the expensive gas

 

It also takes a less expensive gas. That was the main point! Just don't use the 87 octane unless it is an absolute emergency, and take it extremely easy with the car if that situation does arrive.