Last post on Jun 19, 2012 at 3:11 PM
You are in the Automotive News & Views-Archives
What is this discussion about?
#1 of 74 87 vs 91 (or 92) Octane?
Nov 25, 2011 (1:23 pm)
I've always believed that if 87 octane is specified by the manufacturer, then you're wasting money to use 91 or higher. However, recently a friend sent me the following link regarding a serious test using a dynamometer that indicates otherwise.
I sometimes drive my 2011 Honda Fit Sport 5M really hard on nearby twisty mountain roads, constantly accelerating (with all its mighty 117 horses) to red line. So I plan to put in a couple of tankfuls of 91 octane (as high as it gets around here), to see if I can feel a difference.
Now, what do you think, and why?
#2 of 74 Re: 87 vs 91 (or 92) Octane? [andysd]
Nov 30, 2011 (12:14 pm)
I'd say it's generally a waste of $ to spring for the higher octane stuff. However, if you're running the piss out of the thing which causes it to run hotter than nommal, then it may be worth something.
You can usually hear if you're getting detonation (a pinging / knocking noise). If you notice this while running hard, you may want to spend the extra $ on higher octane.
#3 of 74 Re: 87 vs 91 (or 92) Octane? [andysd]
Nov 30, 2011 (1:13 pm)
This brings up an interesting question. In the bad old days, a car designed for higher octane (premium) gas would suffer from destructive detonation if run on lower octane (regular) gas. Conversely, a car designed to run on lower octane gas did not benefit from using the higher octane.
However, with the modern engine management systems, most (or all) cars designed to run on higher octane gas can run on a lower octane with diminished performance but no damage.
The question is, do some (or even all) cars designed to run on the lower octane gas have the capacity to benefit from a higher octane? If some but not all, which ones have this capacity? Finally, if such cars exist, how do they differ from the ones designed to run on a higher octane gas but able to use the lower octane gas?
#4 of 74 Re: 87 vs 91 (or 92) Octane? [andysd]
Dec 01, 2011 (7:24 am)
The original posting has received two replies, but no one has watched or commented on the video that was the reason I started this thread. The video is an objective search for the real answer, not just opinion, including dynamometer curves, to learn whether the conventional viewpoint is valid that there is no benefit to using higher octane gas than specified by the car manufacturer.
I do know that using lower octane in a Mercedes can cause damage. When I had one, a '94 C280, I heard a service guy explain that to a customer, showing her a carbon-encrusted internal engine part he kept on his counter.
Someone, please watch the video: http://www.europeancarweb.com/tech/proven/epcp_1007_2010_volkwagen_jetta_proven/- - viewall.html
Just copy and paste it to go to that location.
#5 of 74 Re: 87 vs 91 (or 92) Octane? [andysd]
Dec 01, 2011 (3:30 pm)
Actually I did watch the video (well I read the text; I didn't realize that it was a video.) In fact, that test, which showed a Jetta which specified 87 octane fuel performing better on 91 octane, was the genesis of the questions that I posed in message 3.
#6 of 74 Re: 87 vs 91 (or 92) Octane? [bhill2]
Dec 01, 2011 (6:40 pm)
Hi bhill2 -
Sorry, yes, I see the point in your last para of Reply 3, and I forgot it was only text and graphs. I know the 5-cylinder VW engine isn't a barnburner - even my Fit has a better 0-60 time - so maybe it's the sort of under-stressed engine that would benefit from higher octane.
I bet a lot of people won't accept that there would be any improvement to engines specified for 87. In fact, I'm still on the fence.
Today, I ran my Fit hard in the mountains starting with a full tank 50% 91. It felt great but it always does. Now I'll run it to near empty, fill up with 91, and get a seat of the pants impression.
In the other direction, I special-ordered new a '99 Z28 that I still have. The manual specifically says it's ok to use 87 with lower h.p. I phoned the GM techs to be sure. Since I don't need all that h.p., I've been using 87 in it for years, getting 30.2 mpg door to door San Diego-Indianapolis-San Diego because sixth gear is 1,750 at 75 mph. Engine is in great shape with about 65k miles. But if the manual required premium gas, I'd never use regular.
#7 of 74 Re: 87 vs 91 (or 92) Octane? [andysd]
Dec 02, 2011 (8:15 am)
Sometimes an engine can benefit from using higher octane than required/recommended but it is rare AFAIK.
For instance, my 05 Passat with the 1.8T requires a minimum of 91. Around here, 93 is common so that's what I use. If I were to run 89 or lower, the computer would compensate for that which results in lower MPG.
My 00 Odyssey states in the manual that if one were to use 91 isntead of the recommended 87, the HP will increase from 200 to 205. I've used premium a few times in the van and to be perfectly honest, I couldn't feel the difference.
IIRC, C&D did an article on this a few years ago in which they did their road and dyno tests to see if there was a benefit of using premium in vehicles rated for regular. The results were there was not a benefit.
Dec 02, 2011 (11:07 am)
Not going to use regular even if the car might somehow compensate for it. "Only" means something, especially to finicky engineers.
Old car gets the good stuff too, even if I am tempted to run my homemade gasoline-benzol-alcohol mixture
#9 of 74 Update 87 vs 91 (or higher) Octane
Dec 12, 2011 (7:42 am)
12-12-2011 Update: Now the gas in the tank of my 2011 Honda Fit is all 91 octane. It certainly seems more powerful by seat of the pants; I don't give full gas as much; it seems to pull better at full throttle high rpm; seems more tractable at low rpm; and the fuel consumption gauge seems to have jumped 10% from 30 to 33 mpg. Not scientific observations but I am tending to believe it helps.
#10 of 74 Re: Update 87 vs 91 (or higher) Octane [andysd]
by Stever@Edmunds HOST
Dec 12, 2011 (8:08 am)
You might accomplish the same thing (assuming anything is really different ), by putting regular "pure gas" in. (pure-gas.org)