Right then, been doing some playing. I have some results, and I have a question.
People are always asking on here about 91 vs 95 in cars that are rated for 91 as a minimum. I've now done a few runs on each fuel, Napier to Palmerston North and return. There's some flat, there's plenty of hills, there's urban, an all round good test track.
SO in a 2008 FG Falcon 6cyl on 91 fuel I was getting 8.7l/100km. $69.81 for the trip.
Same car, same driving style on 95 fuel is 8.2l/100, $68.16 per trip.
Now I've always been a bit of a cynic about this whole topic and I have to say I was really surprised by the extent of the difference. However in reality you're never gonna use 95 just to save money. If you're that hard up you shouldn't own a car. It's about the engine, drivability etc.
So anyway that was interesting. But the question is, will I see a similar result going for 98! To figure out what economy I'd need to see I need to know the price, anyone know the current price of 98!
Disclaimer: no I'm not so anal as to be thinking about the last 5c on my fuel bill. This is all just out of curiosity really.
3tomany,
Aug 23, 7:56am
i recon if you drove it a bit smoother you can get those numbers in the 7s on 91 i have done it
sifty,
Aug 23, 8:05am
I've tried different fuels over the same commute and found no difference at all, economy wise or performance, so I just fill with the cheapest.
(2 litre non turbo jappa-knees wagon a few yrs old)
Like yourself, I was curious after hearing some of the claims made on the likes of here.
budgel,
Aug 23, 9:47am
It will be interesting to see. If the compression ratio is high enough and the Ecu is programmed to advance the engine until it begins to knock and then retard it slightly, there may be some advantage.( Do they all do this these days!)There will comea point past which extra anti knock properties are wasted.
smac,
Aug 23, 10:25am
On that road! Makes a big difference. As above, from Napier to PN I was seeing 8.6-8.7 on 91. But Auck-Napier it was 8.2, so I would expect into the 7's on 95.
smac,
Aug 23, 10:35am
There are definitely claims of improvement with 98, so whether or not it's worth it will come down to the price. Anyone know what it is at the moment! The watchdog sites don't tend to track 98.
smac,
Aug 23, 4:24pm
Anybody.anybody.!
franc123,
Aug 23, 9:12pm
Haven't checked recently but it would have to be in the 2.35-2.40 ballpark by now. Will be very interested to hear the results of your test. What you've done so far really confirms what I've tended to think in that the cost savings/fuel economy gains are negligible and the only benefit perhaps is a smoother,better behaving and more responsive engine, my own trials between 91 and 95 on an older 6cyl carbed Falcon engine gave this sort of result, especially during warm up. It would have been good to have run it on a dyno to see if there were any measurable hp gains, I doubt it somehow. The claims by some that fuel economy is 10-15% better or thereabouts and that another 100km or so out of a full tank in an average car on 95 is possible are nonsense.
jmma,
Aug 23, 9:24pm
BP's 98 octane Ultimate fuel costs around nine cents a litre more than the company's regular 91 octane unleaded, and four cents more than its premium 96 octane petrol.
Off BP website (o:
ralphdog1,
Aug 23, 9:24pm
I keep accurate long term fuel consumption records. 1991 MX5, ran it for about 5000k on 95 and 3000k on 98, the other 100,000k + on 91. No measurable difference in l/100km. 2002 S2000, have done about 5000k on each on 91 and 98, and it is cheaper to run it on 98. And it runs better.
trouser,
Aug 24, 4:55am
With an 11.5:1 comp ratio you would think so.
smac,
Aug 24, 6:17am
That doesn't seempossible when 95 costs 8 cents more than 91! I'd say their website is out of date. The big clue is they mention 96.
dave653,
Aug 24, 9:56am
Why has 95 increased from only 5c/ltr over 91! Typical. reduce the quality, up the price.
trouser,
Aug 24, 12:51pm
It was 3c then 5c now 8c.
extrayda,
Aug 24, 5:11pm
In all of my cars I seem to get more k's out of a tank with 95.Not much more I don't think, but enough to make it cost very much the same as 91 in the end.So why not run 95!I've never bothered to try 98 in my daily drivers, as they are basic cars, so seems a little OTT.Is it a myth that our petrol quality in NZ is a bit crap compared to elsewhere (RON vs whatever the other rating is)!
whqqsh,
Aug 24, 5:20pm
Ive found it depends a lot on the car, getting the full effect of the higher octane depends on how high your compression ratio is. A Chev of mine knew no difference in economy or even 1/4 mile times whether using race fuel, a mix or straight 91, once I put higher compression pistons in the differences were huge
mantagsi,
Aug 24, 6:43pm
FWIW my Caldina 3S-GTE runs like shit on 91 (rough / knocking / pinking), seems happy on 95, but generally goes a bit more economical on 98. The onboard computer averages 9.5 - 10.5km/l on 95, but will stretch to 10.5 - 12.5km/l on a steady trip. Either way it is too bloody thirsty!
robotnik,
Aug 24, 6:46pm
How did you measure the fuel consumption, was it just what your trip computer said! If you did, this is not always that accurate. What I do is fill right to the the top of the filler neck, drive the distance and then refill to the top of the filler neck again. The amount of the refill gives you a very accurate measure of the fuel consumed.
franc123,
Aug 24, 6:59pm
Fair enough, you could always simply use the supermarket vouchers or AA rewards to offset the extra cost of 95, if you feel your engine benefits from it. As for fuel quality, umm dunno, when you see the black sludgy film that is inside a fuel filter after even 20 thou kms if you can be bothered cutting it open to look it does make you wonder how good it is.
extrayda,
Aug 24, 7:48pm
Yep, I use the vouchers when I remember (takes 60 litres to fill!).It just seems that my cars have preferred 95, so thats what I feed them. If 95 was *much* more expensive I might try 91 again, but for the moment happy with 95.
I avoid the Gull fuel, as my cars are older, and I am not sold on the whole E fuel, as from my (admittedly limited) googling experience, it seems that even ignoring other side effects for older cars, you get less energy (BTU!) per litre, so less distance per tank.
unbeatabull,
Aug 24, 8:04pm
You can get quite involved in petrol and Octane ratings.
Essentially, it comes down to what the car is designed for. An older car with lower compression and less advanced timing will show no advantage at all running a higher octane, where as a modern car that is running higher compression and more advanced will run better on higher octane.
Obviously, most modern cars have knock sensors and adjustable ignition so they can still run well on lower octane fuels as well.
Economy really comes down to simply which fuel the engine runs the most efficiently on, that is produces the most amount of torque/power smoothly over it's range without being on something that burns fast like nitro/meth etc.
Performance wise, more advance timing, higher compression, and high octane all go hand in hand with each other.
smac,
Sep 8, 6:32am
OK finished my fiddlings. SO the same driver, same car, same road:
918.6-8.7 l/100km 958.1-8.2 l/100km 987.6 l/100km
So for that car 98 IS actually cheapest.
bellky,
Sep 8, 6:33am
Assuming those^ figures are in fact accurate.
smac,
Sep 8, 6:35am
Agreed, that might be my next job!However if they're not, I would actually assume they are evenly inaccurate. It's the difference that matters, and I would expect that to be ok.
wrong2,
Sep 9, 1:40pm
as opposed to putting $20 in every week & watching the mileage over time !
hahaha
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