95 vs 98 Octane - Fuel Economy Difference

[Rodge]

I've typically had a strong bias toward using 98 Octane fuel in my high performance cars over the years despite the fact that most if not all are rated to run on 95 Octane fuel so out of curiosity I took a bit of interest in a fuel economy test I came across the other day that the N.Z. AA ran comparing the two.

They went about it in a fairly exacting manner, (happy to unpack their methodology more if requested too), but basically they ran a Subaru WRX rated to run on 95 fuel completly empty till it wouldn't start and then put 15 litres of 95 Octane in it and drove for 170 klm's until it completly stopped and couldn't be re-started.

Then they repeated the process with the same car, same drivers, same day and driven over exactly the same route with 15 litres of 98 Octane fuel and you would think with the significantly higher octane it would have more energy content and have gone somewhat further to justify the premium price 98 Octane sells for but it ran for only 1 kilometre more at 171 km's. In my opinion this is probably well within the margin for error even in a well disiplined test like this so the significantly more expensive 98 gave no meaningful distance advantage.

As an aside - (Note in their previous issue they'd compared a car designed to run on 91 fuel using regular 91 Octane and found it gave a 7% distance advantage as compared to using an E10 91 Octane fuel, so even though the theoretical difference in energy content between an E10 91 fuel and regular 91 petroleum is 3.3% they found a 7% fuel economy advantage in using reg petrol, now that's what I call a clear result !).

Now I know that 98 gives you a bit more kick up the top of the rev range but over winter when there's often very limited traction is there much point in using 98 Octane fuel in a car designed to run on 95...thoughts ?

[LTDHO]

Hardly worth spending more on 98 huh!

Simply, put in fuel the car was built/tuned for.

[Rodge]

Note - In N.Z. 98 Octane typically sells for ~ 10 cents a litre more than 95.
What's the typical price premium in Australia ?

[_Ben]

Where I am, premium is between $1.40 - $1.60 + / L. Obviously fluctuates a fair bit but it goes for about 15-20 c/L more than 91, and about 5-10 c/L more than 95.

[TC200six]

I prefer 98 because a number of cars I've driven ping like crazy under load with anything else. I must say I've never heard a late model Falcon ping, so 91 or 95 would be more than suitable for them.

[pottery beige]

98 shut the gate.. bum dyno and ear pingometer tells no lies..

[flappist]

My car was expensive.
It is very important to me as I use it daily and I rely on it.
I use the best fuel and oil I can buy.
I fit expensive performance tyres.
I have it maintained by professionals.

I am not interested in the slightest in risking compromising my transport in order to save enough money to buy a cup of coffee.......

[superfly]

About 10 years ago I did some dyno testing and road testing between different fuels and found that indeed in some cars designed for 91 RON fuel, actually ran a lot better and gave better fuel economy running 98 instead of 91.

I also found that not all cars react the same and that not all 98 RON fuels are the same. In my XR50 I've tested 91, 95 & 98 and came to the conclusion that 95 was worth paying the extra for but not 98.

In regards to the article, they've only tested economy. 98 can also give an extra improvement in power so some people may be happy to pay extra for that too. Best way to answer if paying extra for 98 over 95 is worth it, is for you to do your own testing. Cars are not all equal.

[Peter B - CV8]

The wife's 2007 model Mazda 6 is designed to run on 95 RON. We've owned the car for 4 years, done approx. 80,000 k's, & up until recently always used 95 RON & always got bang on 600k's to a tankful (around town) using fuel from our local BP outlet.
Six months ago, the BP outlet decided to stop selling 95 RON & replace the bowser with a diesel outlet. As a result, we've been using 98 RON. We are now getting around 650 k's from a tankful (ie an extra 50 k's) & the car feels a bit more responsive.

[335POWER]

I always used 95 but gave the 98 a go for a month or so, and found it to be worse than the 95. Fuel economy was worse, and the car felt a bit lethargic. Went back to the 95, everything was great again.

[Franco Cozzo]

The old man's 2003 323 specifies 91 but it pings off its head going up hills on 91, no problem on 98.

[Silver Ghia]

My FG runs sweeter on BP ultimate 98. Just that makes it worthwhile spending the little extra.

[mike_nofx]

So they only did the test once with each fuel type?
Over 170km there would be many variables which could sway one way or the other. 3 times minimum with each fuel type would be a better sample range.
That extra 1km that the 98 ran for, did the 98 run have the car stop on a slight slope leaning away from fuel pick up, for example?

I like mythbusters way of testing fuel consumption. A glass tube on the passenger side window which allowed them to see exactly how much fuel was used over a particular run.
I think relying on the fuel pick up to determine exactly the amount of fuel that is used is not accurate and variation of 500ml-1L difference (depending on slope of the road when the engine cuts out) is not totally out of the question.

Kinda difficult to make out, but heres mythbusters method:

[ryeman]

My understanding is that the higher RON the greater the 'resistance' to ignition....the 'sweet' spot is the min RON that resists pre-ignition, so for my FG I6 95 is it.

[DJM83]

Always put BP98 in all of my cars, dont care. Need fuel so i buy it, i aint gonna argue over a few dollars or kms per tank.

[Mr G8]

98RON only in the Fairlane... Never have nor will use anything less. She's my pride and joy, so I'm not fussed about the finer details

[peteypete]

Okay what I meant to say was:
What is the 100ron at United petrol stations, is it just a re-labed 98ron designed to attract people into buying it from their company instead of others?

[pottery beige]

Originally Posted by DJM83

Always put BP98 in all of my cars, dont care. Need fuel so i buy it, i aint gonna argue over a few dollars or kms per tank.

so much this.. got me stuffed how people spend $20k, $30k, $40k, $50k, on a car then sook and want to run it on watered down kero..

[T4ME]

Originally Posted by peteypete

Okay what I meant to say was:
What is the 100ron at United petrol stations, is it just a re-labed 98ron designed to attract people into buying it from their company instead of others?

Its 98 octane with 10% ethanol added(P100 E10) and on a car tuned for it will see better results than 98 octane.

I have used it for 3 years and always get @550kms to the tank in my BA Falcon.

Put shortly its a better fuel

[Itsme]

Originally Posted by flappist

My car was expensive.
It is very important to me as I use it daily and I rely on it.
I use the best fuel and oil I can buy.
I fit expensive performance tyres.
I have it maintained by professionals.

I am not interested in the slightest in risking compromising my transport in order to save enough money to buy a cup of coffee.......

My car was expensive.
It is very important to me as I use it daily and I rely on it.
I use cheapest fuel and oil to specs I can buy.
I fit cheapest performance tyres.
I have it maintained by qualified mechanics.

I am not interested in wasting money when you do not have to......

My car will last as long as yours.

Gotcha......

PS: never known any difference on performance & economy between 95 & 98 when I had my FG XR6 Ute.

[pottery beige]

Originally Posted by T4ME

Its 98 octane with 10% ethanol added(P100 E10) and on a car tuned for it will see better results than 98 octane.

I have used it for 3 years and always get @550kms to the tank in my BA Falcon.

Put shortly its a better fuel

how do you go with this and availability., i pulled comp out of my Clevo build as i wanted everyday driver.. plug and play at the bowser not with the tune..

[mik]

just my opinion i dont think there would be a lot of difference between 95 and 98 in fuel economy, unless your engine can make use of it or needs the higher octane, my understanding is the higher the octane the less volatile the the fuel ..... ie throw a match in bucket of 98 woomf................ throw a match into a bucket of 91 bigger WOOMF !
most standard engines dont need high octane unless they have been built for it or they are forced induction/high performance, but higher octane fuel affords better detonation /ping protection on all engines, my xr6 has a severe dislike for 91 or e10 pinging its tits off, so it lives on a diet of 95 or better.... usually 98, so in fact 95/98 may be more economical if it keeps the engine safe in the long run.
funnily enough i do hear quiet a few small economy cars pinging their guts out around the burbs , i'll bet they are not using the good stuff.

[burnz]

im in two minds over this.
91, 95, 98 should have the same energy rating, same distance travelled per tank...(assuming no E10 in the mix)

but 98 gives better torque than 91, so less throttle percentage required to do the same job..

[ebxr8240]

All my cars are forced induction.. I vary fuel around so I couldnt tell you..
Carb engines can have issues compared to EFI engines..
Yes I use E10 at times but its a mix.. Even in the GTE...
Usually a tank of 85 or 98 then top up with E10 at the end of week..

[flappist]

Originally Posted by trublu

My car was expensive.
It is very important to me as I use it daily and I rely on it.
I use cheapest fuel and oil to specs I can buy.
I fit cheapest performance tyres.
I have it maintained by qualified mechanics.

I am not interested in wasting money when you do not have to......

My car will last as long as yours.

Gotcha......

PS: never known any difference on performance & economy between 95 & 98 when I had my FG XR6 Ute.

So do you run 95 or 98 in your diesel ranger?

[Itsme]

Originally Posted by flappist

So do you run 95 or 98 in your diesel ranger?

Did you not read my last part of post.

PS: never known any difference on performance & economy between 95 & 98 when I had my FG XR6 Ute.

[flappist]

Keep this on topic and leave out the personal insults.

[T4ME]

Originally Posted by pottery beige

how do you go with this and availability., i pulled comp out of my Clevo build as i wanted everyday driver.. plug and play at the bowser not with the tune..

Pooraka,Prospect,Seaton and Airport have it...not sure about other United's as I haven't enquired.

[flappist]

Originally Posted by T4ME

Its 98 octane with 10% ethanol added(P100 E10) and on a car tuned for it will see better results than 98 octane.

I have used it for 3 years and always get @550kms to the tank in my BA Falcon.

Put shortly its a better fuel

Actually I am pretty sure that United disclosed that it was made from 95 PULP plus ethanol not 98. There was a big promo when it first came out describing how they believed it was better than Shell Optimax which was the first and I think only 98 available.

[T4ME]

That's not what United disclosed to me or what ethanol/gasoline calculations say

Adding 10% of 100% ethanol to 95 octane would give a 97/98 octane fuel where as adding it to 98 gives 100.

The same percentage of ethanol added to a higher base number will not climb as high either.