Gasoline Octane, 95 or 98 Grade?

[bcnz8]

Hi all,

Here in Spain we have possibility to choice Gasoline between two different Octane grade, 95 and 98.

Does any one know how 98 or 95 grade can affect our engine?
I'm everytime using 98, I don't know why, I'm only suppose that more octane,more quality, more expensive, more quality or benefits for my engine, but certainly I have no idea if really there is something important for my Z8.

[RRZ8]

Stick with 98! The S62 engine is equipped with knock sensors that can vary crucial engine settings, the higher the better (although I understand that the S62 can also 'run' on 91....(?))

[thegunguy]

Octane numbers are also expressed/measured differently in different markets.

[macfly]

Your 96 is equivalent to 92 here in the States.

US octane is an average of 2 ratings, research octane (RON) and motor octane (MON). If you look at a gas pump in the United States, you will see a yellow sticker that says "octane by R + M / 2" which is the formula for the average. In Europe, they only report the RON.

[Lupin]

more octanes means more vapors , more vapors means better explosion
Higher compression ratios will make gasoline engines subject to engine knocking if poor quality fuel is used.
So the higher the better

[bcnz8]

Thanks for your comments,

As I logically thought, more octane means better running, otherwise no sense, why pay more for nothing better?
The only doubt was if really I or my Z8 can appreciate this small octane difference from 95 to 98, moreover in Catalonia,(north of Spain) not all gas stations have both types, usally only 95 cotanes is available.
Whenever I can, I go to same gas station and buy 98 octane but in some cases I was obliged to refill with 95 due to the trouble to find 98.

But, now, thinking on RRZ8 and Lupin comments "the higher the better" or "more octane, better explosion" and also thinking that S62 engine was developed to run from 91 octane (I suppose 91 USA octane), it's clear that 98 is fully better.

I addition, thinking on thegunguy and Andrew comments, I was searching the USA vs Europe Octane equivalency and found following information:

91/92 PON (USA) means 95/96 RON (Europe), and US "Premium" 95/96 PON means 98/100 RON (Europe)

[zed8]

I was advised to use 95 RON by the authorized service.

[macfly]

91 octane is the highest rated gas we can get here in California for many, many years, so I'd guess that is the baseline the S62 would have been designed around. According to the info I can find that is equivalent to your 95. Anything higher will be better, cleaner, kinder to your motor, but may not give much of a performance difference.

[bcnz8]

Thanks Andrew,

Whenever possible, I will continue using our Europe 98 RON.
Moreover, price difference is not to high, 95 RON is 1,13? and 98 RON is 1,25? (average prices in Spain)

[RRZ8]

A few years ago I did some testing regarding octane with my previous X5 (4.4 V8). After several tanks of gas I clearly found that, when city and highway mileage stays constant the octane 98 fuel economy was abut 15% HIGHER than the octane 95 mileage (i.e: 7 kilometers per liter (98) instead of 6 kilometers per liter (95)). At first I did not believe that this difference was 'constant'. It was after about 5 tanks of gas (about 450 liters of testing) of each octane that I believed it. One of the mechanics at my BMW dealer advised me to put the 98 in and explained that it is fully logical; the engine has a more efficient output because the 98 simply 'explodes better' and thus the fuel-economy will improve.
This of course means that the perfomance (horsepowers) will improve when 98 is used. (this is of course the reason that BMW advises to put in 98..)

[Lupin]

I moved from the US to Switzerland in 2008 with my z8, so now I am ALWAYS using 98 oct., and I have noticed a better result in the "sound" of the engine. It is more consistent especiallly when you start the car.
Even if the chart suggest a little difference .
And regarding the economy I always heard that you make more mile per gall. and it makes perfect sense.

[bcnz8]

About better sound and better running, this is something that as I've said I had doubts, my subconscious tells me that works better ...but this is the same when you drive your Z8 just finished washed: seems to run perfect!! ...also the sound seems better!

Anyway it is clear that we all agree to use the highest octane we can for our Z8.

[Lupin]

Also,being in the biz, let me add that in USA now everybody is mixing the gasoline with 10 % ethanol.
With the Ethanol the water blend with the gas much more, the separation between the gas and the water is less , so the filters can do very little or nothing.......So be very careful where you put gas and try to stick with the same place that you trust and you should use a major brand.

[macfly]

I know, as a motorhead I find it disgusting that the Corn Lobby in Washington is powerful enough to influence what we goes into our cars, and removes our freedom of choice in so doing. What about that level of corruption is democratic? Like everything in this tragically broken and corrupt country, nothing!

[thegunguy]

As you know, I have quite a bit of background in the renewable area, including ethanol, and I can say with certainty that there is nothing economically defensible about our corn subsidies, ethanol production methods, or use of ethanol as a replacement for MTBE. It's all rather quite shameful.