95 vs 98 Fuels

[Cambo351]

Shell V-Power is 100 Octane over here

From my experience at least, naturally aspirated engines don't respond much to increased octane over the specified grade. i.e. it's spec'd for 95 octane, running 98 makes bugger all difference.

However with forced induction engines there is more potential.

One example with the XJR on my road trip from the UK to Switzerland.

I filled up in the UK with Esso Supreme 97 octane, this got me to the Dutch/German border, driving across Belgium I was getting around 11-12 L/100km.

I filled up with Shell V-Power 100 octane at the Dutch/German border, and got an impressive (to me at least) 10.1 L/100km from there back to the Swiss border.

It should have actually gotten worse since I was driving faster in Germany than in Belgium...!

[aualright]

Originally Posted by mex351

Why buy 91 when you can use 98 and your car will run better cooler and be more fuel efficient? Hell I use 98 for the mower and whipper snipper too and TBH the cost of it pales in significance against the cost Jim Beam cans ever since the Alcky Pops tax scandal...Grrrrrrrrrrrrrrrrrrrrr

So yes I use 98 even in my standard XF Ghia,our EF,our FG XR6 sedan and my ute (with a additive) and don't care about the price.

I'm with you Mex. My 4 stroke ride-on, chipper, brushcutter and other 2-stroke yard machines all drink 98. The 2 strokes feel like they spin faster and don't get bogged down as easily in the long paddock grass, but then again maybe it is in my mind?

The additional cost is insignificant at the end of the day. But then again, I don't drive 10km to the next servo to save 2 cents per litre, nor do I line up on the 'cheap' days to save a penny that has been spent anyway waiting for a pump.

****

[Percy351]

I average 10.5-11 l/100 km around town and low 8's in the country in a BFIII wagon running on 91. A little better on 95, but same or worst on 98.
Get 12.5 l/100 towing a bike trailer with 2 bikes and car fully loaded on 98 sitting on 110-120 kmph.
I prefer to use 98 when towing as it does increase performance plus it helps clean out the combustion chamber.
I think the only advantage of 98 is that it contains better additives to keep the engine clean.
Some 91 fuel does not contain any additives at all causing more deposits.
I have found BP98 is the most consistant as it seams the most popular and has the highest turn over so you always get fresh fuel.
Everyone has their own opinion, good luck

[Kieron]

Here's a reasonably fair comparison -
http://video.au.msn.com/watch/video/...petrol/xl3pd1w

In the second test in the above video, the biggest gain was going from 91E to 95 with a 4km gain, 95 to 98 was a 2km gain. All cars identical, all with 3l of fuel and all driven virtually identically.

The way I see it is higher octane fuels don't contain more energy, they are simply harder to ignite/ flame front travels slower. This means they resist higher pressure allowing an engine designer to up the compression which in turn, produces more power and more advanced timing.

If an engine isn't designed for higher compression/higher octane fuels, the only thing that can be done is advancing the timing to take advantage of the slower burn rate of higher octane fuels using a knock sensor. The ecu essentially keeps advancing the timing until a knock occurs with the goal being to get the flame front to reach the piston top at say 10degrees atdc (entirely dependant on rod ratios, stroke etc) which might be the optimal point for a given engine.

Given the above, I don't get how whipper snippers and lawnmowers can get extra power as they typically don't have ecu's and knock sensors, it would appear to me that they would in fact lose power due to slower flame propagation. Same applies to an engine without a knock sensor.

[The Yeti]

In the wife's grocery getter, it's E10 all the way I can't (try as I might) get her to go
Non E10 regular ULP

In her 38 she will drive past 3 servos with the gauge on E- looking for a non ethinal 98ron fuel

This thing is fussy as, e10 91 it will just tell you it's not doing it,
Regular 91 it will say er ok but I don't want to 95ron it'll do it and won't complain to much but tells you it wants 98,

[ltd]

Originally Posted by Kieron

Here's a reasonably fair comparison -
http://video.au.msn.com/watch/video/...petrol/xl3pd1w

In the second test in the above video, the biggest gain was going from 91E to 95 with a 4km gain, 95 to 98 was a 2km gain. All cars identical, all with 3l of fuel and all driven virtually identically.

The way I see it is higher octane fuels don't contain more energy, they are simply harder to ignite/ flame front travels slower. This means they resist higher pressure allowing an engine designer to up the compression which in turn, produces more power and more advanced timing.

If an engine isn't designed for higher compression/higher octane fuels, the only thing that can be done is advancing the timing to take advantage of the slower burn rate of higher octane fuels using a knock sensor. The ecu essentially keeps advancing the timing until a knock occurs with the goal being to get the flame front to reach the piston top at say 10degrees atdc (entirely dependant on rod ratios, stroke etc) which might be the optimal point for a given engine.

Given the above, I don't get how whipper snippers and lawnmowers can get extra power as they typically don't have ecu's and knock sensors, it would appear to me that they would in fact lose power due to slower flame propagation. Same applies to an engine without a knock sensor.

This.
What's occurring in your engine at detonation of the fuel air mix is simply a chemical/thermal reaction used to drive a solid object downward.
I have run an NA6 on all petroleums, and a BF loves the 91 octane without ethanol. Premium 95 or 98 did nothing, in fact it drank more on the 98, on par with the 95. There was no power difference, and that is because this engine was locally designed to run on the local fuel which in this country at the time was 91 octane.
I've asked several people repeatedly including my father who worked at caltex as a chemical engineer for many years and frankly, the only time when a premium fuel can have an advantage over the placebo is when the engine can adapt through either timing, induction or compression. No ifs, and or buts.

[ryeman]

12-1 is LPI ONLY cos its octane rating is ~110

[Windsor220]

Higher octane fuels definitely do something on some engines. Depends on how they are set up. My old Laser was the only car that I ever felt a difference from and it was quite noticeable.

One thing I don't understand is people saying a certain brand of fuel makes their car run bad. 95% of fuel comes out of the same refinery. Well it does here in WA and I'm guessing its similar in other areas.

[ryeman]

I guess it's commercially sensitive information and no one who has all the facts is going to spill the beans, so it will forever be a secret.....come on out and tell us, we dare you!

[XrRabbit]

Twice I have out 91 in my car in over 12 months. Can tell the difference between 91 and 95. I can't so much between 95 and 98. Not more power as such, the car just works better. Better acceleration, run alittle cleaner, and gets better fuel
economy. I only let the car get down to half a tank and I can normally get an extra 50kms out of a tank. Is worth that little extra money

[XrRabbit]

Originally Posted by Windsor220

Higher octane fuels definitely do something on some engines. Depends on how they are set up. My old Laser was the only car that I ever felt a difference from and it was quite noticeable.

One thing I don't understand is people saying a certain brand of fuel makes their car run bad. 95% of fuel comes out of the same refinery. Well it does here in WA and I'm guessing its similar in other areas.

I noticed that in tassie where I used to live that for some reason using shell and catlex 95 octane where very different. I could get an extra 20+ kms from caltex then shell. I tested the 2 over a few months, trying different shells and catlex's. is very weird

[xtremerus]

Originally Posted by XrRabbit

I noticed that in tassie where I used to live that for some reason using shell and catlex 95 octane where very different. I could get an extra 20+ kms from caltex then shell. I tested the 2 over a few months, trying different shells and catlex's. is very weird

20 Km difference to a tank is SFA.
Easily a variation of temp, traffic, wind direction, to name a couple of variables, can produce this much error.
Just the filling of your tank has a large variation that could account for more that in error.

[Kieron]

After reading this thread, I thought I'd try 98 in my manual FG XR8 which requires 95.

I use Caltex 95 normally so tried their 98, I haven't done a scientific measure but I haven't noticed better mileage or power increase. What I have noticed is its got better 'drivability', anyone with a manual fg xr8 will know they aren't the smoothest of beasts but on 98 it's noticeably smoother with its power delivery, particularly down low. I'll run a few more tankfulls of 98 then switch back to 95 and see if I notice the difference switching back.

[Josh G]

My BF XR6 has had cold hesitation/stalling issues for well over a year now. Changed just about every sensor known to man - however upon changing the fuel pump and PCV, it's been running not too bad on 95, the occurrence of hesitation decreased significantly, but since putting 98 in, the problem's returned and the hesitations are longer than ever. Could it be a computer/PCM issue perhaps, given the car is not liking the fuel? Nothing to do with perhaps a crook batch - happens across the board be it Vortex or BP Ultimate etc.

[OwnTheRoad]

Some have mentioned that they use 98 in 2 stroke and small bore motors, as many manufactures claim this fuel is more dense it can have an adverse affect on small bore motors , 4 strokes I've noted can foul plugs particularly if it's a cold environment or higher altitude as the fuel won't turn to vapour as easily in such a small motor.Stick with the engine builders specs I suggest.

[2242100]

Originally Posted by Josh G

My BF XR6 has had cold hesitation/stalling issues for well over a year now. Changed just about every sensor known to man - however upon changing the fuel pump and PCV, it's been running not too bad on 95, the occurrence of hesitation decreased significantly, but since putting 98 in, the problem's returned and the hesitations are longer than ever. Could it be a computer/PCM issue perhaps, given the car is not liking the fuel? Nothing to do with perhaps a crook batch - happens across the board be it Vortex or BP Ultimate etc.

I had rough cold idling problems on my stock untuned FG XR6 Turbo that started a couple of years after moving to my present cold, high altitude location. It had been an annoyance for a long time, but not bad enough for me to get around to doing something about it, and I've used 98 since the car was new.

But recently I changed to 91 fuel after running the tank almost dry. I did that to see how much acceleration advantage the car was getting from the 98 fuel. It was driven for about 50 k's with some full throttle driving before the next cold start and unexpectedly the cold idling problem disappeared.
I ran two 91 half fuel loads through the car and then went back to 98 with no further problems since then, although that was only a bit over a month ago. I'll be interested to see if it comes back in the winter (in view of "OWN THE ROAD's" post).

If your car is a Turbo I'd expect you to lose a reasonable amount of power on 91.

My reason for the change to 91 was to see how much performance loss there would be and although the car still felt very fast (because the initial throttle response felt just as good as it was on the 98) my GPS based Performance Box told a very different story.

According to it (the same accurate device that MOTOR Magazine has been using) the car lost 10% acceleration on full throttle under virtually equal weather/load conditions.

[MercurySilver]

i fill up with 98 and it always goes over 600km on the dial

the old ute gets 91 but sometimes ill give her some 95 when im filling up with lpg

[THE SLUG]

I run my AU I6 on regular unleaded 91, I won't put E10 in it. I've tried 91, 95 and 98 octane and have noticed very little to no difference in terms of economy between the three, the only difference is it's every so slightly more spritely on 98. The one thing I have certainly noticed though is that BP regular unleaded gets me about 50km more to a tank than Caltex or 7/11 unleaded, so if I can I always go for BP fuel! Can't comment on the difference between the different brands of premium though.

*edited

Just like to add that it runs beautifully, gets 500km to a tank of city only driving and pulls like a freight train all on 91