What octane gas do you use?

[crystalworks]

Originally Posted by trader4

Well documented by whom exactly? Show us the test report. JCL just
said that his best MPG ever was with 89 octane, no retarding of timing,
no decrease in performance, no difference in performance with higher
octane, etc. He said that 87 had only a small difference in performance, he
didn't quantify it beyond that. If it's a small difference, without repeating
the test many times, controlling the conditions, etc, it doesn't prove
much one way or the other. He can explain what he meant by small
difference, it could just be a difference in performance, not MPG. I've
said all along that if I wanted to do 0 - 60 test runs I'd use high test.

And he's the one that said using 91 or more was throwing money
away, not me. Premium is about 20% more and if I or JCL was
getting 20% or more better MPG to justify it, I think we'd see it.
All I saw was a variation of about .1 or .2 MPG one way or the other
and not always in favor of the higher octane fuel either. Twenty
percent would be ~ 4MPG. And I also never recommended anyone
do anything. Someone started this thread asking what octane people
here use and I simply told them what I've used for 100K miles now.
Just the facts.

As always, your car, your money, your choices.

My apologies then. I was reading your posts as a recommendation to others and mixed up the throwing away money comment.

You're right, it doesn't increase fuel economy THAT much. I think I saw a difference of 1-2mpg when using premium vs. 87. Not a significant difference and depending on routes/conditions could be even within the margin for error. I did however note the change in the car's responsiveness. I realize some won't (maybe even most people) notice in the way they use their vehicles during their commute.

Completely agree on the your car, your money, your choices.

[JCL]

I didn't say using 91 was throwing money away, I said that if there was no performance or fuel efficiency difference on your local fuel, then buying a higher octane fuel was a waste of money. Your engine isn't getting a treat or making more power or burning cleaner. Octane is simply a measure of resistance to detonation. If the fuel isn't preigniting, then higher octane is irrelevant.

This ignores the effect of greater quantities of detergents, or less ethanol, which different grades may contain.

Saying that all must use xx ignores that fuels differ widely in different geographic areas, which is well documented.

Also, when considering retarding the timing due to knock, consider that it isn't all or nothing. Let's say a typical driver with varying loads and engine demands uses 87. It won't retard the timing all the time, it may be as little as a few percentage points of the time. The rest of the time it drives just like with a higher octane rating. That is why many won't be able to measure a difference.

I used 87 occasionally, but I could tell a difference in how the engine ran. I don't recall the fuel economy numbers, I discounted using it because I could tell. Sometimes I used premium because that brand used less or no ethanol, which matters. Sometimes I used premium because of seasonal conditions, and temperatures high enough to matter. Sometimes I used lower octane because of being at higher altitudes which didn't require higher octanes.

If all that is too complicated, fine, just put 91 in it and call it a day. But claims that actually using the correct fuel for the conditions are somehow cheaping out are absurd. At the time I had my X5, my employer paid for all my fuel, and I just paid tax on the personal benefit. So using the correct fuel certainly wasn't because of cost.

Also note that different engines respond differently. My X5 had an M54. The X3 has a more highly tuned engine that responds more to 91, so it gets it most of the time, still some 89 depending on conditions. The 535 definitely liked 91, but came alive on 94 with no ethanol, so those are the two fuels it got.

[thrillcat]

Prices also vary regionally. Here in Iowa where ethanol is pushed very hard, we have 87 with or without ethanol, and either 89 or 91. Few stations offer 91, and pricing right now is $2.65 or so for 87E, $2.95 for 87 and $3.65 for 91 (my station doesn't carry 89). So it's closer to $25 per tank more for me to use ethanol. I only fill up once a month so it's not a huge deal.

That said, a couple months ago I tried filling up with 87 w/o ethanol. Didn't notice any difference. This month I'm trying the ethanol blend. I won't be putting it in again. Same mpg, but I feel a pretty noticeable loss of power.


Sent from my iPhone using Tapatalk

[J.Belknap]

Originally Posted by crystalworks

Is your Dinan badge connected and all one piece? Mine is separate letters and looks a little different...

Originally Posted by tmv

About to ask the same question

It is the original style.

[jljljl]

Only Shell 91
I want to try 93, but never found a spot that has it ..

[crystalworks]

^You won't notice a difference going from 91 to 93. Or shouldn't anyway since the engines ECU optimizes for 91.

[JCL]

Originally Posted by crystalworks

^You won't notice a difference going from 91 to 93. Or shouldn't anyway since the engines ECU optimizes for 91.

You won't notice a difference due to the AKI rating. You may notice a difference due to the ethanol content.

We have 94 with no ethanol, 87 with ethanol, and everything in between is a blend at the pump.

[Joshdub]

Yeah your 94 is like rocket fuel. When I had my A4 I had a map for 91 and a map for 93. Fill up with 94 go juice and switch maps, and it was like a whole new car. Then when that ran out I would be disappointed until I returned to Canada.

[bcredliner]

The ECM will reduce timing if the octane of the fuel is insufficient to prevent knocking. At that point the 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 premise being that the quality of the fuel may not meet the specified minimum. Since the knock sensors prevent hearing knocking the timing may be retarded without your awareness. The benefits of higher octane fuel 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.

While these variables apply to all racing I suggest it is fair to consider that racers have always sought the highest octane at the pumps or race gas and would always be confident the octane stated would be accurate because over a quarter of a mile times would be better. Racers never risk spark knock due to low octane fuel because of how destructive it is. From that I don't think it unreasonable to suggest that improvements in times, from pump gas to race gas, will also result in an improvement in daily driving mileage from using higher octane than the specified minimum. That improvements in track times indicate an improvement in all around engine efficiency which would include mileage even mileage in racing conditions.

I have no idea how well fuel is regulated to assure what comes from the pump is what it says it is so I use only one station of name brand gas when I am around home. On the road, I get gas at a well maintained name brand station that appears to pump high volumes. I'm guessing that what I get will be what I want.

[jdstrickland]

Using Regular in an engine that prefers Premium is a false economy. Modern engines will detune themselves if the fuel grade is too low and results in engine knock/ping. Knock is bad for an engine, so if it is detected then the computer will retard timing to prevent knock from happening. The result of detuning is reduced performance that most drives will not feel in the seat of their pants.

You should keep a log for a while of using Regular gas, and then repeat the log using Premium. You want to calculate the COST PER MILE, you do this by dividing the MPG into the price per gallon.

Lets say that using Regular, gas costs $3.50 and you get 20 mpg, the cost per mile is 17 cents, 17.5 to be precise. Now lets say that on the tanks of Premium you get 23 mpg, and the price per gallon is 3.70, the cost per mile falls to 16.1 cents. Premium costs less to use than regular because it is more efficient, greater than the difference in price.

I pulled numbers out of my ass to illustrate the point, your numbers will be different but the point is still valid and you need to know what the numbers are before you can jump to the conclusion that lower price fuel costs less to use. You might be surprised to learn that the higher cost to fill the tank pays for itself.

Cost per mile is what you want to know, not miles per gallon.