Octane ratings.....what's the truth?

I know this is old stuff, but I would like some input (hopefully informed) on current thinking, now that gas prices have skyrocketed and there is a real financial significance that just didn't exist "in the olden days". Here in British Columbia, Canada we are paying $1.17/litre in $Cdn or 1.17 x

3.785 (l. / U.S. gal) x .86/1=$3.80 U.S. / U.S. gallon.....and that's for regular. Let's look at about $4.10+ U.S. / U.S. gallon. The book for my car 2001 V70xc recommends a minimum octane (RON) of 91, and I see regulars at 87 and mid-range at 89. I listen to Radio Station KGO (San Francisco) at night and often hear their science Guru Bill Wattenberg (PhD etc. etc. knows all, et al) who says, "If it will run on regular, use regular. A modern sophisticated car engine may not run initially that well, but sensors will "re-tune" to the lower octane and will be fine.....no damage.....no power loss.....no effect on warranty. The theory, as I understand it is that "higher octane" doesn't mean more "power" in the gas, it means elements added to adjust combustion rate. In his opinion higher octanes are "generally speaking" a scam on automobile users perpetrated by the oil companies and encouraged by the auto manufacturers.

What's the consensus?

Gerry

Reply to
gerry
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Ah.... the Truth. There is no truth, there is just perceiption. There also is no consensus on this I am afraid. And since when is truth determined by consensus? ;)

Anyway... MY EXPERIENCE is that the higher octane fuels will cause the engine to run more efficiently, somewhere around the same percentage as the price is higher. So... if the higher octane stuff is around 10% more expensive, then I get a milage that is around 10% better. This has been "More Or Less Accurate" (= True? ;) ) since the first time I did the calculations for my Saab 99. Since this car did not have any "intelligence" built in (you had to get in the car first yourself) it didnt adjust to the fuel by itself. So.... I got fed up with tuning to a different fuel and did the calculations. In the end I stuck with the higher octane fuel.

If I was/had an oil company, I would make sure my fuel was priced so that i would sell the most, OR make my profits as high as possible. If my high octane fuel did not have enough benefits, then I would have to lower the price OR improve the performance of it. So..... I suspect this has been going on in the oil-markets for a while, and the prices will have leveled out related to the performance.

That is my GUESS. That is not the truth. ;)

BTW: The best way to save on fuel cost is... ... not drive. It is easy to drive 10% less. Try it. It is the truth. Ehm.... oops! ;)

Good luck. Richard.

Reply to
Richard

Sounds like about the same prices they are paying in California.

If your owners manual says 91 RON, you should be OK with regular. Pump octane is RON+MON/2. RON is the higher of the two numbers in the numerator and is sometimes used in other countries as the pump octane displayed, hence it being quoted in your Volvo manual.

You can figure this out for your own situation yourself. Run a few tanks of regular, then a few tanks of midgrade over the same conditions. Keep track of your mileage and fuel costs (forget the # of gallons, it doesn't matter). Assuming the engine does not knock or ping, make the calculation for miles/$ instead of miles/gal. If you do better with the midgrade repeat the experiment with premium vs. midgrade.

Who cares what the consensus is? Do you only vote for the projected winner in an election? Can't you form your own informed opinion?

Reply to
Fred W

Then you should run it on the 91 stuff. Is that considered premium?

In the UK we have a different scale, ordinary unleaded is 95 RON, super is

97 upwards. You can buy 102 RON. :)

Hmm. Octane is the opposite of cetane in diesel. The higher the octane, the harder it is to get the fuel to burn when compressed - which means you can squeeze it harder for a bigger bang.

A higher cetane rating in diesel means it will burn easier when compressed.

Ignore him and try it yourself.

Generally, turbocharged cars like higher RON ratings, 'cos the fuel:air mixture can be squeezed harder before it detonates. Pre-detonation is A Very Bad Thing, also called pinking. Saab donks for the last X years, where X is many :) have had a knock sensor that adjusts the ignition and reduces power to avoid pinking. If you have a turbocharged Saab petrol engine and you run it on a lower RON fuel, it'll produce less power or damage itself. Run it on higher RON stuff and it'll produce the most it can, subject to tolerances / ignition curves.

Not put especially scientifically... :)

That Bill Wattenberg is an idiot?

As Fred says, who cares? Suck it and see. But, if your handbook says 91 RON and you try 87 RON, you _may_ invalidate any warranty, but I don't know of a modern-ish donk that could damage itself like this, merely run like a three legged cat (i.e. lumpy and not as good as it should). :-)

Reply to
DervMan

Here's more of the same...

"Retune" is total BS. It doesn't retune and start running as well on regular. It *de-tunes* and reduces power so that it can run on regular. Big difference. Higher octane gas is not a fraud - certain engines will not run as rated with lower octane. Scientific fact for the SF guru who knows all.

Some claim that 89 octane is oil company BS since cars are only rated at 87 or 91. But, 89 might be a choice for people like you who want to go a little lower and see how it works for them.

Using higher octane *will* let your turbo run with more efficiently and with more power. Whether your particular style of driving, in your particular terrain, with your right foot will gain or lose MPG is dependent on all that. If you work out the minor % difference in price vs. the sometimes large 2-3pg change in mpg, using lower octane gas is usually a money loser.

But, conditions vary. Try it, see how you do.

Reply to
- Bob -

I normally use Shell Optimax in my 1993 9000CSE 2.0 LPT, 131k miles, but the station on my route was closed for 3 months, then I used Morrisson supermarket fuel (regular only). The engine was OK but not sparkling, there were occasional flat spots which I put down to maintenance, filters etc. Recently changed back to Optimax, and it feels like the engine has been 'cleaned up' as it runs smoother and more consistently. Apart high Octane, quality fuels also contain cleaning agents. Exhaust systems used to be something which lasted for 3 years or so, but I'm really surprised that the exhaust hasn't failed for 6 or 7 years since a box was last time replaced. Wonder if that may have something to do with better fuel quality?

Reply to
johannes

formatting link
Check the above link out - is fairly imformative

Mickx

Reply to
Mick x

The same as the pdf you posted, thx. (But better not post pdf here). The performance aspect is just one part of it, though in practical terms, I think that quality fuel is healthier for the engine.

Reply to
johannes

I fully agree. I use V Power in our Areo Conv with Hirsch upgrade and Audi A6 Quattro 3.2 FSI and notice the difference.

Reply to
Mick x

Gerry,

FYI, and since nobody has mentioned it yet, 91 RON is about the same (within

1 octane point) as 87 AKI octane that your local gas station is pumping as regular in Canada. You might get better acceleration and gas mileage with higher octane, but if you don't need the acceleration and your engine spends more than a bit of time warming up because of cold temperatures, the low octane fuel is more economical. Wattenberg might be a bit off in the details (probably to simplify it for his radio audience), but I agree with his general philosophy. If you had an AERO, I might adjust my answer. That is were Wattenberg's "generally speaking" part kicks in.

Walt Kienzle

1991 9000T
Reply to
Walt Kienzle

Actually the higher the octane rating the less the thermal enrgy in the petrol. Yet it goes quicker ! Funny that isn't it ?

Don't listen to any jerks who tell you to ignore the manufacturer's recommendations btw - no matter how many PhDs they may have. Foolishness knows no bounds.

Graham

Reply to
Eeyore

Speaks volumes. He's a loonie.

Mind you most *American* cars are so low-tech that they don't care about octane rating it seems.

Graham (who once had a car that *required* 100 RON octane petrol)

Reply to
Eeyore

Actually it has more to do with the different methods of measuring octane around the world.

91 RON is aprox. = 87 AKI (the common octane unit of measure in North America) 100 RON is aprox. = 94 AKI, which is available as premium in many parts of North America. 103 AKI racing fuel is/was available at a few petrol stations I visited.
Reply to
Walt Kienzle

So you're saying if you have an Aero (I do, 9-5, 2002) that "generally speaking" high-octane fuels ARE a scam? Why?

Reply to
Gary Fritz

Well, kind of, it shows that an engine with the relevant sensors can handle higher octane fuel. I didn't see any mention of the handbook of the M3 saying something like "maximum power on 95 RON xxx bhp, maximum power on 97 RON, 360 bhp..."

Because they *do* say that...

Reply to
DervMan

But, no. Indeedy older tech cars cared very much about their fuel, because unlike modern stuff they can't adjust themselves on the fly to cope with different fuels.

If's a different scale though.

Reply to
DervMan

Other way around. The High Output Turbos in Aeros can make better use of higher octane fuel than can the lower pressure turbo engines.

Reply to
Fred W

In my experience over thousands of miles, the LPT equally benefits from high octane fuel. Minimising fuel cut outs at maximum power. Reducing flat spots. The cleaning agents in some quality fuels are also worth having.

Reply to
johannes

No, I am saying the opposite because, generally speaking, high octane fuel is not needed. AERO's would be one of the exceptions.

I'm glad you didn't say you have a Supercharged Buick Park Avenue. That car confuses me, I haven't determined if it follows the exception or the rule.

Reply to
Walt Kienzle

"Not needed" is not the same as "You get no benefit from it".

Reply to
Dave Hinz

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