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I always use 95RON min on my 1MZ-FE mostly because our 91 is crap. Definitely can feel improved acceleration, economy also although have not proved this conclusively with multiple fuel economy tests - need a really consistent right foot & weather conditions.

Edited by ZZT86
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These days I always fill with 95 or 98 octane in both my Atara SL's. We live in regional Victoria often making long trips (2 or 4 hours each way) I agree the cars do feel more responsive and  yes have tried standard fuel at times but I do get better km's to the litre & performance from higher octane fuel. There once was 100 octane available from a United fuel station in Bendigo and that was really hipo ! I often filled with 100 octane going 950km's to Sydney, My cars loved it. They no longer sell it due to poor sales.

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Another thing to note - petrol heads prefer Hi Octane so YMMV :| Can vouch for United 100, used it on my gen7 celica occasionally & it woke up instantly, not that it was asleep. Again, I'm of the opinion that petrol in Oz is absolute rubbish & not the RON they claim it to be but much lower.

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To answer the OP question in short form, Yes you will net a minimal gain but with a large caveat.

The responses in this thread seem to be quite speculative. Higher RON fuel merely means it has a higher resistance to knocking within the engine. It doesn't mean more powerful fuel, purely because the number is bigger. If the engine has the capability to take advantage of the fuels higher resistance to knocking then it will do so and possibly yield a slight gain in power. The injectors are still going to push the amount of fuel required for this. Meaning if you drive on the same piece of road, in the same conditions, with same driving habbit you will yield a slight gain as the engine will make a tiny bit more power so you dont need to accelerate as much to get to the same speed. If the weather is different (air density and temperature), the load on the engine (driver induced, terrain etc) then the outcome will be different. A higher octane fuel doesn't magically push less fuel through the injectors. The engine is going to push through what it needs.

The other point to note too is if the engine is tuned only upto a certain RON, there is a good chance it won't take advance of the extra reduced knock feature so therefore a higher ron provides no gain in terms of resistance to knocking. Meaning if the engine is tuned for 95 octane to create its highest power output, putting 98 ron in won't magically create more power or gain better fuel economy. It simply means you've met the minimum specification of 95 ron and gained a few extra points of resistance to engine knocking. 

A classic example is E85 fuel vs conventional 100% petroleum fuel in a turbo car. Turbo engines gain a greater benefit from higher octane fuel such as E85 because of the ability to adjust the engines compression. Hence why you will see a huge gain in performance from high octane fuel, as the engine itself can be pushed harder (more boost, more timing) with a fuel higher resistance to knocking.  

Simply putting higher RON fuel into a standard engine without variability in compression and timing change is really going to make minimal difference. Thats why when people go E85 tunes you need a custom ECU, and all the fuel mods to support it.

I too have also put 100ron into my old 7th gen celica and it made literally 0 difference to engine performance but i did get about 20% worse distance from a tank. ive tried all manner of fuel in my 600cc and 1000cc bikes, my 2JZ and 7M turbo even my 370z and i literally never noticed any gain in power or economy if i went to a higher grade over what its tuned for. Granted on the turbo engines i've had them custom tuned to run a higher RON fuel and gained power, but certainly lost economy as a consequence. But all the NA engines that have a static compression ratio, then no gain.

Also to the claim that Aus fuel is some how worse than anywhere else, what is this based off? just a feeling? Put it this way, if you put 91 ron into an engine that needs 95 ron, it will still run and run absolutely fine, but when you start to drive up a steep hill, tow a trailer or put immense load onto the engine the engine will start pinging and theres a good chance you'll get some knock. 

So with your idea that Australian fuel is worse and less RON than claimed....let me ask you this. By putting in the minimum ron fuel grade specified for your engine,  have you ever experienced any knocking or pinging at all? My point being, if Aus fuel is **** and lower RON than advertised, then you will get the exact same symptoms. If you put 95 in and the car runs fine on 95 then how is it worse?

Ive been driving and working on cars for nearly 18 years and never once experienced any of these gains from power or economy just using higher ron fuel or losses from crap aus fuel, so i think there is a bit of a placebo effect where people think higher RON number + price = better performance. But thats just my opinion, everyone's experience can vary :D

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So if your average car is designed & tuned to run on 91 octane fuel but you really have 89 octane or less in the tank will the car produce the same power & give you the same mileage as was intended & at what cost to the engines longevity ?

I'm not aware of any variable compression engines - care to mention some ?



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3 hours ago, Thirteen said:

Also to the claim that Aus fuel is some how worse than anywhere else, what is this based off?

I have previously read this article about Australian fuel quality. My thought at the time was that this could explain why latest engines are not being made available by manufactures i.e. Toyota for the Australian market.


1 hour ago, ZZT86 said:

not aware of any variable compression engines

These engines have been under development for quite some years. Now becoming a reality before 2020 but not expecting Toyota to be adopting this technology until it is proven in production



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Well in your situation if its tuned to run on 91 fuel then using 91 octane fuel will be the optimum source of fuel to power the engine to produce the optimum power and torque and have no side effect of pinging or knocking. If you put in 89 RON, i suspect you would notice barely any difference in normal city and slow driving, but it would become alot more prevalent at the other end of the spectrum, so if your towing heavy loads, racing the engine driving up mountains in tall gears and just putting a heavy load onto the motor. However depending on the engine if the ecu is capable of making an adjustment for such, then it should retard the timing to compensate. The same can go the other way too. However most modern passenger cars are built to a budget and these features can be negated. In terms of longevity, it depends how its treated, i assume you only mean if everything is looked after and the fuel is the only variable. If you drove it gently and off load and avoided pinging and knock then whatever the engineers deem to be the life of the engine would be it. If you race the engine hard and its pinging and or knocking, i suspect not as long. But its like anything i knew a guy that had a GTR Tuned specifically for 98ron, the engine was in very good condition and it still chucked a rod,  My point being the answer is very wide because its a broad question.

Cars that come out of the factory are generally built in such a way to get the most life for the most economical cost. Not only in terms of servicing but also to the consumer. 

Sure, there are many variable compression engines, but im using it as an abstract term, Subaru WRX, Toyota Supra RZ, Nissan GTR, Mazda RX7, Toyota Hilux Diesel, anything with a turbo fitted too it. If you check the compression off boost the ratio is generally lower than a non turbo engine, hence why they feel sluggish until boost kicks in, as the turbo makes up the gap in lower compression and more in boost pressure. A turbocharger works by forcing compressed air into the motor to push up the compression in the cylinder.

Edited by Thirteen
removed word ratio
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My point is if the fuel is bad or lesser than minimum required then the ecu would have to retard timing based on info from the knock sensor, ie: if the engine is pinging its head off. Some cars are so bad I hear them before they even pass me. The ecu is a learning/adaptive device but it can only do so much to protect the motor, the rest is up to physical strength & time before it all goes kaboom, hence why I use a higher octane fuel than recommended. I also have a very sensitive butt dyno 😉

I'm aware of variable compression engines in the pipeline as @campbeam has pointed out above but not aware of any currently on the road. My understanding is you can vary boost pressure on the intake but the engines physical maximum compression does not change until Nissan & others release their stuff in the next year or so.

I got a wake up call regarding a lot about tuning when I got to see ecu logs of different fuels on the same motor. On 98 the engine has its timing reduced as it silently pings away reducing maximum output & acceleration for a given rpm, on E85 there is little if any ping & is able to perform to it's potential without retard in timing giving maximum acceleration. Not saying everyone should run E85 because you can't without a tune at least but it's an extreme example of the difference in knock/ping versus our fuel type/RON used.

The higher the octane the higher the resistance to knock.

Edited by ZZT86
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7 hours ago, Thirteen said:

A turbocharger works by forcing compressed air into the motor to push up the compression ratio in the cylinder.

No, turbos do NOT change the compression ratio.  The compression ratio is literally the difference between the volume of the cylinder at bottom dead centre compared to top dead centre ("static compression ratio").  This changes slightly during operation due to valve timing (and then called "dynamic compression ratio").  Whilst the actual cylinder pressures in a turbo- or super-charged engines on-boost will be much higher, their compression ratios are almost always lower than naturally aspirated engines (and do not vary regardless if the engine is "on-boost" or not.  Forced induction pushes more air MASS in to the cylinder (since the volume is fixed).


In a normal engine (turbocharged or not) static compression ratio (which is the number everyone always refers to) can only be changed by skimming the head, using a different thickness headgasket, or fitting domed/dished pistons or ones with a higher/lower wrist pin.  Forced induction engines traditionally use different pistons compared to their NA sisters 


In simple maths - take two engines, both with a compression ratio of 10:1, one turbo and one NA.

The NA engine breathes in air and fuel at around atmospheric pressure, call it 1bar.  The piston then compresses this air and fuel mix to 10bar (10:1 ratio).

The turbo engine uses a turbine to pre-compress the air before it is drawn in to the engine, a turbo running 1bar of "boost" will push air and fuel in to the cylinder at 2bar of pressure (1bar atmospheric + 1bar of boost).  The piston will then compress this mix further to 20bar (note this is still 10:1 ratio). 


However, because the turbo engine has injested double the fuel and air, it makes a big chunk more power when it is burnt.  There are a lot of simplifications there, but the whole point of a turbo is to boost the volumetric efficiency of an engine (actual amount of air drawn in per revolution compared to theoretical capacity of the engine)

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  • 1 year later...

What's everyone's feeling on e10 fuel. i just happened to half fill the tank with it this morning.

i was half expecting some sort of problem, but actually i think the car is running a lot smoother.

Anyone else found this ?

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