bc

Okay you all will probably want to kill me for asking this yet again but I'm seeking a definitive answer to this question. I have read the numerous threads and see lot's of opinions but I still do not know what the real answer to this is yet.

I have never used the minimum grade octane in any vehicle because I always felt that engines ran a little better and a little cleaner with highter octane. I don't have a CAI yet so that doen't come into play in this question. I just can't bring myself to run 87 in my 06 GT, so for now I run 89. I read here a few things that higher octane burns slower and I read where someone said Ford claims that if this vehicle is meant to run 87 that higher octanes can produce carbon build up. To top it off I called my dealer and asked to talk with the head of the service department. I say 'Is it okay to run 89 in this 06 Mustang and could it cause any problems'? He says quote-unquote 'No it won't hurt it at all. 89 octane is just a better grade gasoline'.

So which is it for sure? If the 06 GT is stock and tuned for 87 octane does it do any good at all to run 89 octane and on the downside can running 89 octane create carbon build up. I know this is a forum so what I may get back will be opinions and I don't mind opinions, but does anyone have a definitive answer on this question? Thanks in advance.

Bob

Scott P

Higher octane means it is more resistant to detonation. If you car is designed to run on 87 octane, then running 89 or higher octane really won't make any difference. You sure aren't harming the engine at all with 87. The 87 is not a lower grade of gasoline. It's all in your mind.

W1ldcat

Won't hurt and if that's what you like, then go for it.

Sonic Boom NH

The short answer is no, it doesn’t do any more good for your motor, gas mileage or horsepower to use a higher octane UNLESS you have a custom tune designed to use a higher octane.

So if your stock stick with 87 octane as 89 and 91 will not do anything for you, you gain nothing.

One reason for higher octane in custom tunes is because generally to get more horsepower the tuner advances the timing. There really is no other way of getting more horsepower out of a vehicle other then shoving more air (oxygen) and fuel at it, in a given time, and your motor can only suck so much air in unless you stick a supercharger or turbo on it.

Nitrous Oxide is another alternative of shoving more air (oxygen) and fuel in the motor without having to have a supercharger of turbo. Then you can also double your fun by seriously shoving more air (oxygen) and fuel in the motor by using both a supercharger or turbo with Nitrous Oxide.

So once you get into adding more horsepower your going to need to buy the expensive 91/93 octane. Other then that, for a normal daily driven stock car 89 and 91/93 is nothing more then putting money into the oil companies pockets because it will NOT do anything for you, well except maybe make some people feel warm and fuzzy.

Same goes for the stupid octane booster you see being sold in Auto Zone and all auto parts store. Octane boosters like 103 is nothing more then a gimmick because they do NOT raise your octane at all. To do so would take perhaps 50 bottles of the stuff and then you might raise your 87 octane to 89 or 91 but just cost a lot more…

Here are a few websites you might want to check out:

http://vettenet.org/octane.html
http://auto.howstuffworks.com/question90.htm
http://www.straightdope.com/columns/041008.html

bc

Thanks for the replies so far and thanks for digging up those 3 links Sonic. Interesting reading. I'm guilty of listening to what a lot of people believe about gas all these years (ie: that premium runs cleaner and provides better performance in any engine), without ever having researched the facts. So this is good stuff. Interesting what the one article says about switching gas every 5000 miles so that the additives in the new brand will attack the deposits in the previous brand. I wonder if that actually has scientific fact behind it. Seems to me you build up deposits from the additives in one gas and then start building different deposits from additives in the new gas, but then again maybe he bases his recommendation on fact.

But what I gathered from the 3 articles was if you hear knocking then it might be time to switch to a higher octane. My first impression of all this is to just switch back to 87. But since our engines have knock sensors that retard that effect how will we know this isn't occuring I wonder? Oh man...catch 22 I think.

JewStangGT

i've always used 87

Sonic Boom NH

Generally you wouldn’t know unless you’re very sensitive to your vehicles performance. Once the computer senses the motor knocking it will retard the timing to eliminate it. If you were to data log and monitor the timing you might be able to tell but with newer technology it’s not like when knock sensors first came out and basically retarded timing period.

Now what happens is the motor may only have one or a few different cylinders that are having pre-ignition (knock) and the computer will retard the timing (delay the spark) to only those specific cylinders thus making it very hard to tell your timing has been retarded, unless of course your data logging specific cylinders.

If you have bad enough pre-ignition (knock) to actually hear it then its pretty bad and then you might want to try the next higher grade of fuel such as 89. However, generally speaking, if you do hear knock with 87 your chances are pretty good you just got a tank of bad gas and if it’s a full tank you might have to take it easy and live with it till you get about ¼ tank to empty and then fill up at a different station.

In any case you’re safe going with 87 octane even if you get some bad gas as the computer will take care of any issues for you. Stay with reputable gas stations and you should have no problem. Avoid gas stations that don’t have much business or the mom & pop types that don’t stay real busy selling gas. Chances are very good that at stations that are not real busy could very well have some water in the gas from the gas sitting around either collecting condensation and/or water leaking into their fuel tanks.

bc

Thanks again for the reply Sonic. I think I will just go back to 87 and if I can't hear or feel any problems (which I probably won't seeing how the car only has 2200 miles) then I'll stay with that until I get a CAI and a tune. When I first got it I ran 87 for 2 tank fulls and heard a ticking sound when idling. So I switched to 89 but still heard the ticking sound. I took it to the dealer service department foreman and he said that sound was just the fuel injectors. (Of course this is also the same guy that told me that they ABSOLUTELY would NOT cover any engine or transmission warranty work if I put a CAI on. But that's a different thread. I plan on taking the CAI off, reflashing to stock before I take it in for multipoint inspections...and if they ask me why there's no history in the PCM I have a better one then the battery needs charging. I installed some new Infinity Rear speakers and the instruction manual actually says to disconnect the battery before installing the speakers. That's a great one ain't it? )

Bob

Orion_240

If you feel better paying 20 cents/ gallon more than go ahead!
That's only $2.80 per 14 gallon fillup. One fillup per week and it's only $145.60 a year!
You do have a money tree in the backyard, right???

BoidMorphs

I had my car custom tuned with 93 octane gas with mods of a CAI and catback Borlas. The tuner tried advancing the timing but said my car didn't like it so he backed it off a bit. I asked him to give me an 87 tune just in case I wanted to run cheaper fuel. He said it was easy. He'd only need to make a timing change. A few weeks went by and I went back to 87 octane gas and loaded the appropriate 87 tune. I got less than 2 miles from home getting on the highway when the engine coughed and went into the safe mode. That was scary and I didn't realize that stopping the engine and restarting would reset everything in terms of the motor running "normally" again. I took it easy and since it was a holiday weekend I couldn't reach the tuner at his shop. I decided to load the 93 tune and run on 87 octane gas. I was careful not to get on it hard but slowly pushed it a little harder. The holiday passed and I called and told the tuner what had happened. He said as long as the car was running properly then just keep everything as is.
I can go WOT and the car runs absolutely no different with 87 octane gas then it did with 93 so I have to say why the heck waste the extra money on high test gas? In a N/A car I don't think it's necessary and my car is proof of it. Maybe when I put a power adder on it then that's another story. I think it's a joke everyone thinks their car is running better because they put higher octane gas in. It's more psychological than anything IMHO.
After I get my long tube headers with X pipe installed I'm going to have it dynoed and retuned on 87 octane gas the way I should have had it done to begin with.