95 versus 98 Octane initial observations

[Novicebutnice]

Greeting everyone,

I have recently on both here and Youtube flown the flag of  "98 Octane is the best for every unleaded car" , but a recent driving holiday has caused me to question this.

So.....I decided fairly recently (last week) to fill up (circa 54L of a 60L tank) using BP 95 Octane fuel,

And immediately my cars expected range to zero increased versus filling up with 98 octane fuel.

I usually reset my trip computer, as well as my "average since last reset" to compare if the car is giving me truthful information (comparing what it says my average has been, with how much fuel I have used), and it is usually within tolerance (unknown accuracy of the pump etc taken into account it is fairly accurate,or at least accurate enough) 

So I can say that every time I fill up with 98 (which is nearly always BP) my car gives a range of 600 KM, which I always thought to be bleak because the range figure never increases even when driving on the highway, it just reduces slower or at times just gives what I call strange figures (seems to show a lower range than I would expect given how much fuel is in the tank, and then figures this out and seems to show correct information....)


And now on to the point of this post, I have filled up twice with BP 95 Octane fuel, once from nearly empty, the other from half full (the pump claims from memory without checking the reciept 33 L of a 60 L tank), and on both occasions the predicted range displayed was: 710km

Which means that by buying slightly lower Octane fuel which is also cheaper, I am getting more range.

The next day after filling up (the first time) I drove up to Katoomba from Southern Sydney, and made no attempt to reduce fuel consumption by cruising at a lower speed than the speed limit (and sometimes a tad....), and the average fuel used up to Katoomba from Sydney was from memory 7.4L per 100km

Perhaps if I was doing constant highway speeds, and cruising at higher than the legal speed limit (necessitating a higher engine RPM) the 98 Octane may come into play,

But in city driving, as well as cruising at the highway speeds we have in Australia, for a car tuned for a minimum octane of 91, anything over 95 seems to have the opposite effect.

It is almost as though the timing can't be advanced enough (for a number of reasons like insufficient load, or any more advancing may cause back firing etc ) and so it seems to have the same effect of running a lower octane fuel in regards to fuel burn (range).


I'm a bit curious now as to what range figure using 91 will give me (predicted), but dare I subject my car to that??

And I don't use energy efficient tyres..... 

 

Edited August 25, 2020 by Novicebutnice

[KAA]

Interesting post thanks Stephen, I tend to use mostly 91 or 95 if the price is good..I have never used 98 as it was always so overpriced and i don't use a lot of right foot, I noticed the difference obviously of the 95 when on the highway on long trips..but as we have all been driving way less and any interstate trip is a long way off I mostly use the 91..I have only ever used the cheapest E10 unleaded once..when having no choice but to use it or run out as all the higher pumps were empty at the only petrol station in a small town, so put in enough to get me to a bigger town and then filled up on the 95, using 91 I have never had an issue the car runs like a swiss watch always so to risk 91 I doubt you will have any problems.

Keep Safe

KAA

[campbeam]

2 hours ago, Novicebutnice said:

I'm a bit curious now as to what range figure using 91 will give me (predicted), but dare I subject my car to that??

Certainly expect a lower range figure using 91 instead of 95. If you want a ballpark figure try 10% such that the increased price for 95 is offset by improved fuel economy.

I have just returned from a driving trip of 3800 kms using Premium 95 unleaded instead of the usual 91 unleaded. This was with my 2006 Aurion which now has has 220K on the odometer. Average fuel economy [with V6 2GR-FE engine] was 8.2L per 100kms outbound and 7.8L per 100kms homebound. These are real world figures. I was travelling at the speed limit mainly 110kph and not sparing the horses when overtaking. In contrast, previous road trips have been Brisbane to Wagga Wagga using 91 unleaded and average fuel economy was approx. 9L per 100kms [from memory]. After this latest road trip, the engine and transmission are both at peak performance. I am more noticing smoother pickup and lower engine revs when at speed limit plus also drop in revs when the foot is off the accelerator. So impressed that I am staying with the premium 95 unleaded. 2nd last refill was with Premium 98 unleaded and I did not notice any difference.

Perhaps you could trial using 91 and see if you notice any immediate difference. Newer vehicle and different engine etc may give you a different experience but personally, I would stay with premium 95. With vehicles tuned for using 91, it comes down to the manufacturer's tuning map whether Premium 98 will provide any benefits.

[ZZT86]

I'm a little confused, are you trusting/using the cars trip computer figures or conducting your own fuel economy by filling tank taking note of fuel qty pumped noted on docket, burning the fuel then refilling tank & doing the math on fuel used ? I know that with my previous cars the trip computer was never very accurate & always trusted my own tests instead.

Another thing to note is that the cars ECU will take some time usually a few hundred kms to adjust the fuel trims, smarter cars adjust fairly quickly. Higher octane should give you better everything, imo.

[campbeam]

Some entertaining YouTube videos from our good mate John regarding high octane petrol. 2nd video is an updated version of the 1st one.

 

[Novicebutnice]

18 hours ago, ZZT86 said:

I'm a little confused, are you trusting/using the cars trip computer figures or conducting your own fuel economy by filling tank taking note of fuel qty pumped noted on docket, burning the fuel then refilling tank & doing the math on fuel used ? I know that with my previous cars the trip computer was never very accurate & always trusted my own tests instead.

Another thing to note is that the cars ECU will take some time usually a few hundred kms to adjust the fuel trims, smarter cars adjust fairly quickly. Higher octane should give you better everything, imo.

Hey mate,

I use the claimed amount of fuel pumped, and I take note of the amount of KM's driven and do the maths.

I then reset both the trip computer, as well as the "average since last reset"

The car's "avg since last reset" is usually fairly accurate enough based on what I have found (given that I cannot gauge how accurate the fuel pump is, as well as being unable to account for variance in fuel density due to different temperatures)

Cars normally taking a few hundred KM's to adjust to new fuel trims based on each fuel (understandably if I go down in octane and it starts pinging I would expect it to adjust pretty darn quick), in that it takes time work out a map for that fuel is why I never wanted to chop and change between fuels.

I felt that I wouldn't get a proper result, in that I had heard of higher end car's straight away giving a different range after refilling with fuels like E10 etc, but I thought that my Camry would take time to adjust.

But seemingly my car sensed the different fuel within about 200 metres of driving and displayed a larger range to empty, then it had ever done with 98 (after refilling)

Which means that for whatever reason my car's ECU was not able to advance the timing enough to be able to get the most out of 98 Octane fuel.

Whether it is an imposed limitation of the mapping because it is tuned to run on a minimum of 91 octane unleaded, or a number of other reason's I'm not sure.


All I can say at the moment (with provable figures) is that the cars predicted range to empty using 95 is 710km versus 600km filling up using 98 octane fuel


And If I was to predict (with no provable evidence, based solely on how I feel the car drives) the power curves between the two fuels, on how they affect my car I would guess (at the moment):

95 octane achieves power noticeably sooner and peaks in the rev range a bit lower than the 98 (so I would say low to mid-high end power)

Whereas the 98 Octane takes more time to start making decent power, and it peaks noticeably higher in the rev range (so I would say mid-high to high end power), at which point you run out of Revs, or the car up-shifts (and you are back in mid rev ranges....).



 

[Novicebutnice]

12 hours ago, campbeam said:

Some entertaining YouTube videos from our good mate John regarding high octane petrol. 2nd video is an updated version of the 1st one.

 

Hey mate,

I definitely agree that anyone who see's 98 octane as liquid Schwartz and that it add's X amount of power is mistaken.

But I'm sure that I am not alone, but I can feel the power curve (?) difference using the different fuels... I guess you can call me Niki Lauda...  


 

 

[campbeam]

1 hour ago, Novicebutnice said:

But I'm sure that I am not alone, but I can feel the power curve (?) difference using the different fuels...

I think what I am feeling is the increased engine torque and the transmission smoothly dropping down a gear or 2 for that extra launch. 

[ZZT86]

Stephen, it's strange that the trip computer is showing you a big range difference from PULP95 vs PULP98, that's very odd.

Ashley, I've seen those clips before & I kinda agree & disagree with them. The problem with our fuels in this country is that the actual octane level or RON is often lower than what it should be, ie: 91RON might test as 89-90, so your engine tuned for 91 will not produce the factory power it's supposed to. As soon as you put in 95 then this is corrected & the missing power is perceived as extra grunt !

The other problem with fuel is detonation. Higher octane fuels are less prone to knock where the ecu isn't slowing you down by pulling back timing to protect itself from long term engine damage. The higher octane delivers less knock & better performance, it's also a lot cleaner. It will be made mandatory in the near future.

Obviously car's tuned for 98 should use 98 or higher.

ps: I have an ***** just like Niki Lauda but no-one would believe me ;)

[Novicebutnice]

8 hours ago, ZZT86 said:

Stephen, it's strange that the trip computer is showing you a big range difference from PULP95 vs PULP98, that's very odd.

Ashley, I've seen those clips before & I kinda agree & disagree with them. The problem with our fuels in this country is that the actual octane level or RON is often lower than what it should be, ie: 91RON might test as 89-90, so your engine tuned for 91 will not produce the factory power it's supposed to. As soon as you put in 95 then this is corrected & the missing power is perceived as extra grunt !

The other problem with fuel is detonation. Higher octane fuels are less prone to knock where the ecu isn't slowing you down by pulling back timing to protect itself from long term engine damage. The higher octane delivers less knock & better performance, it's also a lot cleaner. It will be made mandatory in the near future.

Obviously car's tuned for 98 should use 98 or higher.

ps: I have an ***** just like Niki Lauda but no-one would believe me 😉

LOL in regards to your comment about having an **** just like Niki Lauda 

I think what may be happening in my car, is that under normal load, and low to mid RPM the ignition timing can't be advanced enough (maybe ECU limitation due to tune, or to protect the engine) to take full advantage of the anti-knock resistance of the fuel

And as a result the mixture isn't burning at the most efficient rate, almost giving the same effect to using 91 octane fuel (which the ignition timing can't be advanced far enough to get the most efficient burn due to the lower knock resistance of the fuel).

And since apparently ECU's won't lean the mixture too much (in an attempt to reduce Nitrous Oxide emissions, even though the car has a Catalytic converter....)

Because leaning the mixture increases the combustion temperature (leading to an increase in Nitrous Oxide emissions, which is also why they introduced EGR valves in cars before they had 3 way Catalytic converters), and also reduces the fuels resistance to knock (which is why in aviation the avgas has 2 ratings, one for Lean and one for Rich: 100/130

It's just a guess,

Because everything else I know says that:

Higher octane fuel = more advance in engine timing = more efficient burn = more KM per tank

Perhaps for my car:

City only = 91-95 Octane (maybe, since I have not tried this yet)

City plus normal highway speeds = 95 Octane (seems to be the case)

Mount Panorama (vehicle speed and as a result higher engine load and higher RPM) = 98 Octane


Just postulating at the moment... 

[ZZT86]

Have you plugged in a scan gauge to check for DTC's ?

[Novicebutnice]

No, but my Engine light isn't on.

Is it worth buying an ebay (?) one?

[ZZT86]

Not all codes trip a CEL & any past codes are also stored for future reference. If you have a good mate mechanic get him to spend 5 minutes to check. They're rarely needed, I got a decent used one recently for a good price on BF which will come in handy for me when I decide to do ATM fluid flush/change as I need to monitor fluid temps for accuracy of filling otherwise I wouldn't have bothered.