What octane gas do you use?

[JCL]

Originally Posted by bcredliner

The ECM adjusts to the octane of the fuel. At some point lower octane will result in less than the rated performance of that engine (mileage, HP and TQ) because it is running at less than optimal efficiency. IMO there is no logic in using octane rated at less than that specified by the mfg. even if there is anecdotal evidence to the contrary.

I think there is some logic in using higher octane than the minimum specified. The benefits may or may not be noticed. I don't think any HP/TQ/ mileage variance realized can be attributed to just octane, there are always other variables I note or more likely for me, didn't note.

The ECM doesn't actually adjust to the AKI of the fuel, it has no way of knowing the AKI. What it adjusts to is the onset of knock, of which AKI is only one factor. That is why, for example, regular fuel sold at high altitudes may be 85 and not 87 AKI. Or why the dealer may tell you to switch to 89 if you have hard starting at low ambient temperatures.

There is no logic in using higher AKI than required to prevent the knock or than is specified, unless you have forced induction and/or a fuel map that takes advantage of the higher AKI. Standard tunes don't advance timing beyond the baseline. This is leaving aside other characteristics of more expensive fuels, such as reduced ethanol or more detergents, which may be the case. But that takes it away from an AKI justification.

[JCL]

Originally Posted by jdstrickland

Using Regular in an engine that prefers Premium is a false economy.

It isn't just about the cost. By keeping detailed mileage logs, for every tank, you can determine your efficiency, in my case in litres per 100 km. With my X5, he best mileage was on 89. That is a pretty good indication that for my driving, and my local fuel, the computer was not retarding the timing.

Saving money was a bonus, but wasn't the reason to use 89 in my case.

If there was in fact a 3 mpg difference, in my case, I would have used the premium, simply to get the performance out of the engine that it was designed to deliver. Conversely, if 89 delivered that design performance, then putting in premium would be a waste.

[JCL]

In a search for more of your gasoline dollars, the oil companies started upselling the benefits of premium gasoline over 60 years ago. Claims like more power, cleaner burning, and 'treat your car right'. This one even claimed that buying premium was an alternative choice to buying a new car.

[TiAgX5]

Ricky got it all wrong when he heard his car would run better with Ethyl in it.....

[motordavid]

+ w/a few of the above...
I have run regular, 'mid grade', and premo of dozens of brands in our '01 3.0, over the past 14 yrs.

Have never had a 'bad tank' regardless of octane or brand, and the mpg has not wiggled much over 105k miles and those 14yrs of the usual stop & go, climbing our mountain road several times per week, lots of trips, etc.

I don't shop for gas, eg driving around to save 20 Cts, nor do I run non-premo to to save any dough: I just buy gas when/where I need it, and pump what 'grade' I feel like using...

Other than an exhaust cam sensor replaced, (code 172, sub menu 12), and a new fuel filter installed for reasonable maintenance at ~ 100k miles, I have not had a 'fuel' hiccup in all these years, running what I feel like running, gasoline-wise.

Anecdotal, and one can pump 91 or 93 every tank, if it makes one feel better about the situ.

By the bye, I had been looking forward to the 'What gas should I/do you use' thread, that comes up on the Jukebox about 3 times per year here, over the past decade.
GL, mD

[Bmwtvboy]

I usually run highest oct. But for a short time I tried 89 and noticed poor mpg and lackluster acceleration. After 200 K miles and regular syn oil changes it runs smooth and fast when I need it to.

[Ricky Bobby]

I love mD's anecotes because I'm sure hes seen the same threads so many times over the years.

I've been putting 93 octane in cars that require 91+ since I turned 17 and started driving a VR6 Jetta. I've heard the adage a million times from people who do nothing but pump regular on their new Bimmer leases and scoff at how much "more I'm spending" on gas vs them, while their Grande Mochalattefrappucino#lovewins blah blah costs them $6.50.

Run good gas, don't run on fumes. Use Techron if you want, maybe some Lucas if you like using lubricating additives. I have a Shell 2 miles from my house so I fill up at their station, most other times its Sunoco or BP. I won't put regular in my X because I like to follow the recommendations of the manufacturer, and with less octane on our cars comes slightly less mpg and performance.

If I didn't have 93 available I would run 91 if that was the only premium offered. I stay away from non-brand stations that most frequently come up on the news for having extremely cheap gas and water in their tanks.

[bcredliner]

Originally Posted by JCL

The ECM doesn't actually adjust to the AKI of the fuel, it has no way of knowing the AKI. What it adjusts to is the onset of knock, of which AKI is only one factor. That is why, for example, regular fuel sold at high altitudes may be 85 and not 87 AKI. Or why the dealer may tell you to switch to 89 if you have hard starting at low ambient temperatures.

There is no logic in using higher AKI than required to prevent the knock or than is specified, unless you have forced induction and/or a fuel map that takes advantage of the higher AKI. Standard tunes don't advance timing beyond the baseline. This is leaving aside other characteristics of more expensive fuels, such as reduced ethanol or more detergents, which may be the case. But that takes it away from an AKI justification.

Oopsie, what I wrote is certainly incorrect. Of course, the ECM doesn't recognize octane. I edited the post. I think I understand the role of knock sensors though since I can't build my own tune I don't delve into the nitty gritty of the overall system. My assumption is that the quality of fuel varies. If the quality of the fuel doesn't allow the tuning map to reach the maximum timing, higher octane would give some assurance the maximum timing of the existing map is reached.

At least at one time some sources of fuel did not meet the quality standards. If that is still the case there could be a greater value (benefits vrs cost) to a source of better quality of the same grade fuel than any potential improvement from higher octane of that same source of fuel.

Right or wrong, I don't acknowledge even professional tests of octane comparisons. I feel there are too many variables and never what I would call a significant difference that the +-error factor doesn't more than cover the results.

[bcredliner]

Don't have a clue as to validity but interesting reading.

Which Gas Stations Sell the Best Quality Gasoline? » AutoGuide.com News

Tech 101 – Octane: the facts and the fiction behind those higher-priced fuels | Hemmings Daily