Gas octane, which do you use?.....

Gas octane, which do you use?.....


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Mike P

c:enter
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any problems? I was using 87/regular since I've owned it. Its been running rough since the new engine so today I switched to the recommended super, cause its finally cheaper than $3/gal. It seems to run better, any scientific proof to this?
 
Premium is recommended, more so for someone like myself who has had a performance tune.
If the computer was pulling out a lot of timing due to knock it may cause your engine to run a bit rough.
 
The LM dealer I bought it from says to use regular..... I've tried both (yes, for more than just a few tanks) and I can't see the difference. EXCEPT THE COST!
 
Same as Steve.. My engine was tuned for 93 octane. It will run on lower octane.. just not as well.
 
Out here we only have 91. I did a two month test one month all 87 and the second 91, eight tanks each. I did not notice any performance issues, although my MPG was less with 87. I don't remember the exact amount, but it was like an extra $1.25 to run 91 over 87 after calculating MPG lose and exrta expense for 91. I posted this here awile back so gas was probably in the high $1.00 range.
 
The LM dealer I bought it from says to use regular..... I've tried both (yes, for more than just a few tanks) and I can't see the difference. EXCEPT THE COST!

Wonder why he would tell you that when they put that notice on the instrument panel and the gas filler door "Premium Recommended"?

Could it be he wanted to sell you the car and was afraid you wouldn't buy if you needed to use premium?
 
jet fuel like Driller probably uses

ROTFLMAO! :laugh:

TECHNICALLY it's not jet fuel but I have been known to use an octane booster. Shhhhhhhhh....!!! :D

Seriously, what you need to know is the Mark VIII has 2 knock sensors, one for each bank. The PCM 'listens' for the slightest beginning of pinging and will agressively pull timing to control knock.

The stock A/F ratio is quite rich throughout most of the power band. Under normal driving in a stock Mark VIII with normal atmospheric conditions, the knock sensors will likely not detect any pinging and you may not notice any performance hit or mileage difference when using a lower octane fuel.

However, not all drivers are the same and not all 'regular' gas is the same. Add the changing effects of temperature and humidity and you could easily have conditions that are prone to causing knock. Especially so on 'tuned' cars with a more lean A/F ratio. The knock sensors should detect even the most inaudible pinging and the PCM will subsequently pull timing to prevent engine damge. IF the PCM pulls timing, performance and mileage WILL suffer. It is quite possible for the PCM to proactively pull timing and the average driver would not notice the difference unless he is tracking the mileage closely.

I always run premium fuel. To me, the additional cost of $0.20 per gallon is not significant. With the current cost of fuel at $2.60 per gallon, the additional 7-8% cost does not deter me from choosing premium.

It should also be noted, my HD F150 runs on a premium fuel tune by Lonnie and gets 15% better mileage - more than enough to make up for the additional cost. ;)
 
In other words - premium fuel has a higher combustion rate - designed for high compression engines.

You might not notice a difference using a low octane fuel, but you are creating higher combustion chamber temps - pistons and valves, since lower octane fuel will pre-ignite (spark knock) in a high compression engine. There is no real benefit to run high octane fuel in a low compression motor designed for 87 octane because of this fact.

An extreme example happened last year at SSHS8. Aric downloaded a high octane race fuel tune into Goldbird - a tricked out t-bird. The owner Mike, had mixed race fuel and 93 octane and did not tell Aric he did not have a tank full of 110 or whatever Aric told him to put in the car, but he had a watered down mixture in the car.

One pass, and he melted the spark plug electrodes on a couple cylinders. Again, extreme, but the same thing toned down a little is happening when you run low octane fuel in a high compression engine designed for premium fuel.
 
Wonder why he would tell you that when they put that notice on the instrument panel and the gas filler door "Premium Recommended"?

Could it be he wanted to sell you the car and was afraid you wouldn't buy if you needed to use premium?

No way..... he didn't tell me that until a few months AFTER I had already bought it and ran the hi-test. He was also a neighbor of mine...2 doors down the street.

BTW, RECOMMENDED does NOT mean REQUIRED.
 
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Thanks for clearing that up. I've always used the recommended octane in my Mark however.
 
The ONLY reason it is 'recommended' and not 'required' is due to the knock sensors and the ability of the PCM to pull timing.
 
I tend to use 93 whenever i can. Sometimes money is tight and i have to use the cheap stuff. I haven't seen a difference either way, but i haven't done any real experimenting.
 
I have made several runs to the Albany, NY area from Baltimore using both grades.... as I don't "get on it" very often and I am usually feathering the throttle, I saw very LITTLE if ANY difference in fuel mileage on those trips. So, when the prices for gas went up...I went for the regular.
 
ok well I haven't seen any mileage improvment but the facts stated alone & the fact that my car seems to not run as rough have convinced me that I'll probably stick with premium
 
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