Having just completed the same run, over and over and over, with the same load, same conditions, I found a large difference in fuel economy, based on brand of fuel...my results are below...

Total distance of each trip 400km...tank used up, and run done again (picking up and dropping off relos at airport)
Same route, same time of day, basically same traffic conditions and driving speed across all trips...

Shell.....91RON...........7.9L / 100km
Shell / Caltex...91 RON...8.1 L / 100km (Half tank of each)
BP.........91 RON..........8.1 L / 100km
Caltex...91 RON..........8.3 L / 100km
United..e10 95 RON....8.7 L / 100km
United....... 98 RON....9.1 L / 100km

so, the question is, what does your magna like drinking?

Cash, pure cash, straight in the tank

I exclusively use V Power in mine.
I have before used Caltex but it somehow seemed worse

Having just completed the same run, over and over and over, with the same load, same conditions, I found a large difference in fuel economy, based on brand of fuel...my results are below...

Total distance of each trip 400km...tank used up, and run done again (picking up and dropping off relos at airport)
Same route, same time of day, basically same traffic conditions and driving speed across all trips...

Shell.....91RON...........7.9L / 100km
Shell / Caltex...91 RON...8.1 L / 100km (Half tank of each)
BP.........91 RON..........8.1 L / 100km
Caltex...91 RON..........8.3 L / 100km
United..e10 95 RON....8.7 L / 100km
United....... 98 RON....9.1 L / 100km

so, the question is, what does your magna like drinking?

Really no benefit using premium fuel in the 3rd gen as there's no knock sensor, my KJ is averaging 11.3 lites per 100 k's that's about 30% around town and 70% on the highway, thats using E10 fuel

DeanoTS is correct, there's no knock sensors in 3rd gens so the performance/economy difference between fuels should be negligible at best. I used a variety of 95 and 98 RON fuels back in my old TJ and there was no noticeable performance/economy gains to be had.

Now I'm not trying to say there's no difference between fuels whatsoever - but the difference in 91/95/98 RON fuels in my 380 (which has a knock sensor) is far more apparent. The most noticeable factor is that lower grades of fuel tend to labour more up inclines.

Comparing 95 RON E10 to 91 RON ULP is not comparing apples with apples.

E10 95 might have higher octane than 91, but it has lower energy content.

Even a car with a knock sensor would show better economy on 91 than 95 E10.

Octane rating is poorly understood by most and independently not a good indicator of economy.

LPG is the best example - it has a RON of a whopping 110.... But is up to 25% less economical per litre than ULP.

The only data there which seems a little strange (but which is not outside realistic variation) is the 98, which in a car like Magna without knock sensor, should pretty much match the 91 ULP - provided it's not ethanol blend. Simple explanations can include ambient temperature, temperature of the fuel when you pumped it at the station, ambient wind (especially for highway driving) etc.

DeanoTS is correct, there's no knock sensors in 3rd gens so the performance/economy difference between fuels should be negligible at best. I used a variety of 95 and 98 RON fuels back in my old TJ and there was no noticeable performance/economy gains to be had.

Now I'm not trying to say there's no difference between fuels whatsoever - but the difference in 91/95/98 RON fuels in my 380 (which has a knock sensor) is far more apparent. The most noticeable factor is that lower grades of fuel tend to labour more up inclines.

I wonder why Mitsubishi didn't fit the 3rd gens with a knock sensor when the second gens had one?

Really no benefit using premium fuel in the 3rd gen as there's no knock sensor, my KJ is averaging 11.3 lites per 100 k's that's about 30% around town and 70% on the highway, thats using E10 fuel
Actually, a knock sensor only enables the use of more ignition advance; it has nothing to do with the ability to use high-octane fuels, per se. As the OP's post clearly shows, the lower-octane fuels the engine was designed for deliver better fuel economy - probably more power, too. That's partly because lower-octane fuels ignite more easily. High octane doesn't of itself connote more power; just a greater resistance to ignition/detonation.

What delivers the greater power you might see with an engine tuned appropriately for high-octane fuel is generally due to more aggressive ignition timing and higher engine compression. Conversely, running a higher-octane fuel than the engine requires may deliver poorer economy, less power and cost more per litre.

Bottom line:
In the OP's case, suppose the 98 octane fuel cost 2.5% more than the 91 octane fuel. Based on his figures, using 98 octane fuel would result in 15% higher running cost than using 91 octane fuel. Likewise, even if e10 95 octane fuel cost 2.5% less than the 91 octane fuel, using e10 would still result in a 5% higher running cost than using 91 octane fuel.

Jdisnow, it would be nice to get a comparison between different RON fuels but from the same supplier.
Have you tried Shell 95 and 98 fuels?

Actually, a knock sensor only enables the use of more ignition advance; it has nothing to do with the ability to use high-octane fuels, per se. As the OP's post clearly shows, the lower-octane fuels the engine was designed for deliver better fuel economy - probably more power, too. That's partly because lower-octane fuels ignite more easily. High octane doesn't of itself connote more power; just a greater resistance to ignition/detonation.

What delivers the greater power you might see with an engine tuned appropriately for high-octane fuel is generally due to more aggressive ignition timing and higher engine compression. Conversely, running a higher-octane fuel than the engine requires may deliver poorer economy, less power and cost more per litre.

Bottom line:
In the OP's case, suppose the 98 octane fuel cost 2.5% more than the 91 octane fuel. Based on his figures, using 98 octane fuel would result in 15% higher running cost than using 91 octane fuel. Likewise, even if e10 95 octane fuel cost 2.5% less than the 91 octane fuel, using e10 would still result in a 5% higher running cost than using 91 octane fuel.

Well a motor with a knock sensor will produce more power from premium 98 fuel then 91 octane fuel, the TR/TS Mitsubishi operators manual list power from both fuels where the TE-TW manual only list the power from 91 ron fuel, I'm just going by what Mitsubishi says , maybe you know more about their motors then they do.

Perhaps you should pay more attention to what I wrote. You quoted it, so why not read it...

Perhaps you should pay more attention to what I wrote. You quoted it, so why not read it...

Perhaps you shouldn't try and prove people wrong when they are only quoting from what Mitsubishi has said about their cars, there was nothing wrong with what I said it was straight from the Mitsubishi manuals, so what are you trying to prove?????

Jdisnow, it would be nice to get a comparison between different RON fuels but from the same supplier.
Have you tried Shell 95 and 98 fuels?

Hi Spetz...
No I haven't tried that (yet)
I was just trying to see if the crowd had any similar experience to me (ie same route, wide range of results for fuel economy based on brand.) and any info on what works best for their magna.

I was hoping to see some sought of commonality (given all of the cars came out of the same factory door) of brand, ron, economy being the best for all.

It appears however all I have generated is debate over iso-octane rating vs specific volatility vs knock sensors vs price of bananas in Botswana.

It appears however all I have generated is debate over iso-octane rating vs specific volatility vs knock sensors vs price of bananas in Botswana.

The RACQ said I shouldn't have tried to put bananas in the tank.... Still I get great economy on the tilt tray truck :-)