NB8 91 or 95 ron fuel?

[Mr Morlock]

I think some just ignore previous posts. The facts presented by "Drive" probably still on line and probably not the only motoring group to do such tests tell you - based on Camry's (91 reco) ranked cost lowest to highest E10, 95, 91. No one argues that you do not get better economy on 95 than 91 but the 9 or 10cents penalty does not bridge the cost per km gap. "Drive" also did the tests for a mix of suburban and country and the results varied. The argument for using a cleaner fuel ( layman's term) is a different consideration and using 95 ilo 91 is one thing but 98 ilo of 91 in a standard tune car ( which 99% are) makes the petrol companies happy at about 15c penalty.

Most roadtesters actually remark about cars having to run on PULP as it is seen as a negative.

Any engine designed to run on 91 will run optimally and if it is not it should be checked by someone like Dann.

[Locutus]

going to a higher octane fuel with no other changes wont benefit your torque production in any way.

i beg to differ. i realise a the humble toyota yaris was tuned to run on 91, but there is a marked difference in the way our car drives when running 95. so much so that when another member of the family fills it with 91 without my knowledge, i can tell the difference almost immediately when i get behind the wheel. you can actually hear the engine ping & retard timing when it runs on 91. perhaps this is because the yaris was tuned in japan, and we have 3rd world grade ULP in this country (i'm not kidding - look it up). i couldn't tell the difference between 95 and 98 though.

also, just filling up with PULP at a brand name station doesn't necessarily mean you are getting quality fuel. i found that filling up at specific petrol stations gave me marginally better economy than others, even though it was the same 'brand' of fuel. however the difference in this case was likely within error tolerance.

I think some just ignore previous posts. The facts presented by "Drive" probably still on line and probably not the only motoring group to do such tests tell you - based on Camry's (91 reco) ranked cost lowest to highest E10, 95, 91. No one argues that you do not get better economy on 95 than 91 but the 9 or 10cents penalty does not bridge the cost per km gap. "Drive" also did the tests for a mix of suburban and country and the results varied. The argument for using a cleaner fuel ( layman's term) is a different consideration and using 95 ilo 91 is one thing but 98 ilo of 91 in a standard tune car ( which 99% are) makes the petrol companies happy at about 15c penalty.

i hope you are not referring to me. i read every post in the thread before replying.

there have been numberous 'scientific' fuel tests performed by motoring journalists, and they all seem to have contradicting results.

i logged my fuel consumption figures over a period of approx 3 years (~2 years of driving the yaris and ~1 year of driving my NA8). i'd be the first to admit that my tests weren't exactly scientific, as the driving was usually done in sydney peak hour traffic, but i used to get a pretty consistent ~20% gain in economy by switching to 95 in the yaris, but there was no noticeable difference in the NA8.

[NitroDann]

If it pings on 91, but not on 95, id call 98 a higher octane fuel, and 91 a lower octane fuel...

Maybe I wasnt clear enough, but that statement is 100% true, if the regular fuel you use has enough knock resistance for your car. And thats probably just like many jap cars and our crap fuel that you have to run 95 in it.

I though I was clear enough that Its true that if your getting detonation your losing power (due to the ecu pulling timing) and bound to lose ring lands, but sometimes i ramble

Fuel quality has a LOT to do with tank maintenence, and one of the occasional issues with e10 is that because its hygroscopic if the station owner isnt keeping the tanks in good nick your e10 could be 5% water.

The reason that no motoring journal can get matching results on economy tests is because fuel economy has NOTHING to do with octane, and everything to do with calorific value.
Petrol is a blend of about a dozen hydrocarbons (and many more trace ones) and when they split crude oil in its parts the chemical engineers have to pick and choose based on what they have on hand what to blend to get us fuel that meets quality standards.
If they have to add a lot of heptane to get the knock resistance up (improving octane) because they are out of a lighter hydrocarbon, we will get a heavier, denser fuel, with more total energy avalable per litre. It will actually weigh more per litre. This obviously changes weekly and doesnt have anything to do with octane, which only measures how slowly combustion takes place.

On a side note, e85 is 110 odd octane, and about $1.10 a litre. You need to use 42% more by weight to run at stoich, but you only squirt in 30% more by volume. This is because its heavier that fuel by 14% or something, i cant remember exactly. Anyways, what im saying is that because we pay for it by the litre we are actually getting 14% better value than we realise, but we arent using 30% more like we think, we're using 42%, so it evens out really.

Dann

[Apu]

Locutus, you've actually answered your own question there. No doubt the car is (supposedly) tuned for 91...but if it's pinging on 91, then something is not right and obviously why you are getting better economy and performance on 95. And exactly as Dann says, 91 then becomes "low" octane.

[Mr Morlock]

The Drive report is still on line. See what you think

http://www.drive.com.au/Editorial/Artic ... leID=59627

[NitroDann]

Its irrelevant.

You could do the test at the same servo every 6 months and get different results every time.

The important part for fuel economy changes with every tanker full.

Dann

[Mr Morlock]

If dann thinks that is irrelevant then I certainly fail to understand why such a conclusion was reached. In what why was the test flawed and or how else would a "tester" draw conclusions and submit to the scrutiny of large reader audience. I very much doubt that SMH and the Age would have bothered if the result was of no value or was not designed properly. The results might not fit some peoples pre conceptions but that sometimes is how tests come out. This report was a real world driving test- the lab tests tell us very little in that they are rarely repeatable on the road.

[NitroDann]

its like saying that saltier chips will give you more energy. Its not the salt (octane) its the calories.

Im sure their test was correct for the fuel they tested. But how are you gonna get a tank of THAT batch?

See what im getting at?

Dann

[hamx5ter]

I'm not technical at all, but yes, hamx5ter is quite happy to run any fuel, 91/95/98 etc.

I don't put in the ethanol ones, and these days seem to put in 95 most of the time.

Either way, the car doesn't run any differently, and mileage doesn't seem to be affected either.

450-470km per tank (about 40 litres?), regardless of fuel or driving style.

Don't really know about engine tuning or anything.

[samx5]

The last time I filled up with 91 octane in my stock NB8a at a small independent station the car started pinging straight away, I went into the next station I could find to add some octane booster (a bit dodgy I know, but the tank was full) which reduced the problem about 50%, but from then I was driving with very light throttle until I used enough of that fuel to make room for some higher octane. Since then I've only used 95 or 98 and it never pings on either. Can't tell the difference between 95 and 98 either, but I'm not going to use 91 again unless I absolutely have to. Don't know if I've got carbon in the engine or something similar that would make it ping on 91 octane, but I'm not going to pull the motor apart to find out & the motor runs fine otherwise. Car does pretty much all metro driving at the moment and is getting consistently in the 9 litres/100km range, which seems normal to me, and I always give it a bit of a rev instead of labouring in 4th gear. Our auto Mazda SP23 also occasionally gets the 'rattle' of pinging when its in 5th gear in the city with 91 octane, but not on 95 or 98. These modern autos get to top gear too quickly in my opinion, sometimes loading the engine unnecessarily. I also understand that Ford Focus 2.0 litre motors have a tendency to ping on 91 even though its the recommended fuel. Maybe the margin for error is a bit tight. As for the MX5, the car is 'telling me' to use min 95 so that's what I'm going to use.

[NitroDann]

Have you checked the timing?

Dann

[Locutus]

If it pings on 91, but not on 95, id call 98 a higher octane fuel, and 91 a lower octane fuel...

Maybe I wasnt clear enough, but that statement is 100% true, if the regular fuel you use has enough knock resistance for your car. And thats probably just like many jap cars and our crap fuel that you have to run 95 in it.

I though I was clear enough that Its true that if your getting detonation your losing power (due to the ecu pulling timing) and bound to lose ring lands, but sometimes i ramble

yep you're right - my comprehension must have taken a bit of a dive after 2am in the morning.

[NitroDann]

Nah, you're alright mate

Dann

[samx5]

Have you checked the timing?

Dann

No, I haven't done so as yet, I'm due for a service soon & will get it checked then. Maybe needs an upper engine cleaner to clear things out, or maybe run on 98 consistently to take advantage of the detergents? Car is running fine, and with a tank only being used once every 3 weeks or so I'm not too worried about the costs. I haven't tried the 91 octane from one of the big companies yet, maybe that will be better and I just got a bad batch of fuel last time, its hard to know. I have seen reports in SA where a lot of water was being found in service station tanks, causing a few problems.

[NitroDann]

The first thing every noob gets told is to advance the timing to 14 degrees, so chances are unless you bought your brand new its been done. If it has you will have to run on 95 or 98. This is a part of what makes this question dubious, as unless youve checked the timing who knows what fuel you should use?

Dann