Can anyone tell me the difference between these 2 fuels as far as economy gains are on a fgxr6 5 speed auto sedan. I have tried premium and found that there is practically no difference in economy. That was with the 95 octane. I am currently running 91 octane and have never run or interested in running e10. Have never tried 98. Car has done 26000kms so i assume it should have loosened up as much as its going to. Bottom line is im trying to justify if premium is worth it. Last time i tried it, it was not (period was over one month) all conditions.

over a long period of time 91 octane will dirty up your fuel system and all other bits and pieces, if you run 98 it should make noticable difference, it does on the earlier falcons. and my mates brand new ve commodore loves the98

Im not necessarily talking about performance, i am talking about economy, is it worth paying the extra 20c a litre? Im not talking about performance or a cleaner burning engine. Do you get more kms out of a tank? I have used 95 octane for 2 months when i first bought it, noticed nothing but lighter wallet and then tried again for 2 months just recently and yes i only noticed a lighter wallet. No better L/100kms or longer range out of a tank.

with my g6e, ive found using 91 to give a ticking noise from the engine. 95 clears that up. 98 gives me a little more k's per tank, but on average its not much considering the difference in price. personally i run 95, and throw in a tank of premo now anad again when woolies or coles give me a bargain docket..

I dont have a FG but I do Have a BA. Ever since I bought the car which had 91,000 k's on the clock I have always filled it up with BP Ultimate. I now have 195,000 K's on the car and it has never missed a beat. Treat your car like your body! if you fill it with s**t it will act like s**t. So save yourself some money in the long run and go for premo and also premo oil. Better performance and better mileage rather than replacing engine components which can quickly add up to thousands! Thats just my honest opinion and if you cant always afford 98 go for 95 and fill up with 98 once every 2 months cant go wrong!!

In the short-term, you are unlikely to gain any fuel economy advantage, unless your engine is already knock-limited ("pinging"). Premium fuel has a minutely higher energy per litre, but it also burns slower - so no measurable net gain.

Long-term, as bry40l says, premium (especially 98 octane) will keep your injectors, intake valves, combustion chambers, etc cleaner, which will give you better economy and performance over time. You can gain much of this benefit by running a tankful of 98 every 3 fills or so.

If 95 octane is specified for your car, you could be doing damage running 91. The combination of compression ratio and timing will very likely cause knock ("pinging" or detonation), but only under high load: heavy acceleration or lugging uphill, especially towing a trailer. Worst case is your pistons or spark plugs get damaged . Best case is the computer detects the knock and pulls timing out, reducing power and fuel economy.

I would be safe in guessing that most of the contributors to this forum experience high load regularly , and most have modified their Fords ("Fordmods" - go figure) so the factory-specified fuel is no longer adequate.

In your case, I would recommend using a minimum of 95, with a tankful of 98 every third or fourth. If you regularly use full-throttle (eg, overtaking), go with 98 all the time. Your car will love you for it.

I've been running shell v power in my car, for atleast the last year. Everynow and then I'd put shell 95 in and by using that still felt lacking.
Fuel is somewhat like beer, 91, light. 95, mids, 98 is the full strength. Even tho you don't get as much you still get drunk the same, you just get there faster...

If you're talking purely about economy there is a hair of a bee's d**k difference. I run mine on BP ultimate 98. I have run 95 before and i got a total difference of about 20k's. BUT that was at a different petrol station and different types of driving as well, so its hard to compare.

In terms of price of 20c different a litre..its not worth it purely based on economy factors.

HOwever, EVERY other factor it is such as factory recommendation, pinging under load due to incorrect octane/RON, wear/tear and longevity on your fuel system over the life of the car.

My 2c anyway

Thanks guys, a few different opinions was what i was after.

Here is some math I did a while back regarding 91/98. Bare (bear?) in mind this is before I "tuned" the car for 98. Car is an EL Fairmont...refer to mods in my sig (minus J3 chip and 98 "tune")

With 98 I would get an extra average of 60-70km per tank (metro/highway = 50/50). Fuel economy for 91 was about 12L/100km which meant I would have needed 7.2-8.4L more of fuel to gain that extra range I got with 98. At the time I think the difference between 91 and 98 was 15c...could be wrong here. Say 91 was costing $1.20 and 98 was $1.35, there was a difference of $9 for 60L in savings, however an extra 7.2L of 91 is needed to cover the same distance as 98 which adds a further $8.64. So technically I could have saved a good 36c. Obviously not a substantial amount of savings.

With a different of 20c however, I would have saved $3.40 accounting for the extra kilometers and fuel needed to cover the distance.

So obviously up to you if you can justify the extra cost...if you are getting an extra 60-70km per tank extra with 98, $3.40 doesn't seem all that much if your car internals are getting a good wash at the same time.

Now with my car "tuned" for 98, I get a hell of a lot more kms compared to 91. Ran 91 once by accident...got a poor 400km out of the tank, 98 gets me at least 500km and you can definitely feel poorer performance.

(note: I say "tuned" because the ignition is advanced to run 98...not because it is dyno tuned for best results)

Just for reference, the fact that it burns slower actually improves economy as it means you can get more power out of the fuel (the octane rating refers to how quickly/slowly the fuel burns - you are paying extra for a slower burning fuel). BUT, in saying that, the difference IMO would be 2/3rds of f**k all - but my friend has '06 BF XR6 and swears that the economy is the same on either fuel due to using more 91 compared to the 98 but YMMV.

This!
Plus I'll add that I have the 5speed auto FG and I was running 95 for a few weeks after first buying it. Switched over to 98 and re-fueled with that a few times before I noticed any difference.
However I did notice some extra power plus on long trips I'd get some extra Ks compared to 95.
Just my 2cents