Does anyone know of a resource listing octane requirements by vehicle model/year?

Forums › Transport (cars, bikes and boats) › Does anyone know of a resource listing octane requirements by vehicle model/year?

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rhy7s

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#2885651 13-Mar-2022 19:41

lxsw20:

It's more down to the engine than the model of car. I can think of 2 Engines put into Corollas over the years that would want 95. (4A-GE, 2ZZ-GE).

Thanks, that's good info, I would imagine the list of engines requiring high octane ratings in Corollas over the years would be small. It will be a while before I can check to see what hers is. It seems like a situation I find a bit with seniors where they interface with industries that have an upsell option, e.g. a neighbour on a 40gb + endless data plan for their basic T9 keypad phone sending a handful of texts and spending up to an hour on calls a week.

cyril7

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#2885711 13-Mar-2022 21:06

lxsw20:
It's more they are running a higher compression. You start running 91, you'll get detonation. Most Japanese performance stuff was designed to run on 100 originally.

Hi, yes as an engineer I totally understand the concept, just saying, everyday Corollas as mentioned by the OP as in use by his MIL are not likely to be high compression performance motors, more likely the most common and typical low rent corolla that only requires 91, period end of statement.

Cyril

mudguard

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#2885718 13-Mar-2022 21:29

My 2019 Corolla uses 91. That's what it said in the manual. My old Civic with an Integra engine gets 98 as that was what it was tuned for when the engine was built.

lxsw20

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#2885745 14-Mar-2022 01:03

cyril7:
lxsw20:

It's more they are running a higher compression. You start running 91, you'll get detonation. Most Japanese performance stuff was designed to run on 100 originally.

Hi, yes as an engineer I totally understand the concept, just saying, everyday Corollas as mentioned by the OP as in use by his MIL are not likely to be high compression performance motors, more likely the most common and typical low rent corolla that only requires 91, period end of statement.

Cyril

While you're most probably correct, it's running an engine that can run 91. If it's a Corolla GT or something like that, its running the exact same engine/tune as a BZ.

wratterus

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#2886545 15-Mar-2022 14:37

Pretty much every petrol car I've owned I've tried 91 & 95 & done the maths in regards to economy vs cost - running 95 has always worked out to be either the same cost, or slightly cheaper, and the car goes better so for me it's a no brainer. Perhaps just a bit of a fluke with the engines I've had (generally twin cam jappas - SR20, 4AGE, 2ZZ-GE, FS-DE, 4G15 etc)

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#2886554 15-Mar-2022 14:46

My rule of thumb is if its an import, run it on whatever the common fuel type was where it came from. I believe Japan has minimum of 95, so Jap imports should be using 95+. We were told told to use 91 on our import, after a couple of tanks, it ran like crap and started knocking. Switched back to 95+ and was fine after that.

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K8Toledo

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#2891757 24-Mar-2022 22:31

rhy7s:

My mother-in-law runs premium in her Corolla unnecessarily thanks to someone saying to do so for peace of mind back in the day and it stuck. Have recently come across a couple of others under similar delusions at a time when saving costs at the pump would you think have prompted people to question how they came to that belief. Does anyone know of a resource that could be used as a quick reference for manufacturer recommendations in this regard?

Check the maintenance/service handbook. Mine stipulates 95 or higher (BMW 5 series). I think a corolla would run fine on 91?

tripper1000

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#2893581 29-Mar-2022 16:02

Read the New Zealand Manual for the model you have.

A central (international) repository would be complicated because not only can the same model with the same engine have different tunes, different specs and different emissions systems in different countries, but the way octane is advertised/rated is inconsistent between countries.

For instance, 91 in the USA is far higher octane than 91 in N.Z. since the USA system averages Ron and Mon, where as in N.Z. the advertised octane is the higher of the two with a +/- tolerance of 1% to boot (usually minus 1% !!!!). What we know as 91 is 87 by USA standards. What we call 98 can only be 94 or 95 overseas, so because your import has a factory placard saying 91 or 95 does not mean it takes N.Z. 91 or 95. Your Mustang with the (USA) 91 sticker may actually need (N.Z) 95 or your Skyline with a 98 sticker many need fuel that isn't even available at the pump in N.Z.

Discard any advice that broadly groups vehicles or countries. E.G. "91 is good in most Jappa's" or "91 is good in most Corolla's".

Also the minimum acceptable rating, is often not the ideal rating for good mileage or the optimum rating for your pocket. With knock sensors and computers, many/most modern engines will self de-tune and remap gear shifts to stop damage from low octane but this kills performance, necessitating you to put the boot in more to get the same performance. While the car accepts the lower octane, it ends up using more fuel. A smart CVT or Auto transmission on higher octane fuel with reduced knock, will short-shift, keeping the rev's lower and improve fuel consumption.

In general, the required octane rating in cars is continually inching up. Just because a model took 91 in the 1980's doesn't mean it still does. Auto companies are being forced to peruse higher economy (as in CO2 per KM or litres per KM not $$ per KM). Higher compression engines harvest more energy out of the fuel so engines are progressively getting higher in compression and higher compression means it needs higher octane.

As you can see it is can be pretty hard to nail down a reliable answer, so running a higher octane can be very good advice particularly in N.Z.

Bung

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#2893587 29-Mar-2022 16:34

tripper1000:
For instance, 91 in the USA is far higher octane than 91 in N.Z. since the USA system averages Ron and Mon, where as in N.Z. the advertised octane is the higher of the two with a +/- tolerance of 1% to boot (usually minus 1% !!!!).

That pessimistic view isn't supported by the Trading Standards testing of fuel samples. In 2018/19 91 was sampled 79 times and bottom 3 samples were at 91 RON limit, the rest were higher.

mudguard

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#2893611 29-Mar-2022 17:17

tripper1000:

Higher compression engines harvest more energy out of the fuel so engines are progressively getting higher in compression and higher compression means it needs higher octane.

As you can see it is can be pretty hard to nail down a reliable answer, so running a higher octane can be very good advice particularly in N.Z.

That was my understanding. However Kia's Nero HEV has a compression ratio of 13:1 and the recommended fuel is 91!

Short of putting it on a dyno with 91 to 98 in it or running tanks of each to work out the mileage I'd go with what the manufacturer recommends.

tripper1000

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#2894141 30-Mar-2022 11:33

mudguard:

That was my understanding. However Kia's Nero HEV has a compression ratio of 13:1 and the recommended fuel is 91!

OP's vehicle wasn't a hybrid.

Hybrid's are a different kettle of fish. True compression ratio's get fuzzy in a hybrid, and throttle position and torque load (contributors to detonation) can be accurately and absolutely controlled by the computer unlike a non-hybrid.

Hybrids use a (pseudo) Atkinson cycle, as opposed to traditional engines that use the Otto cycle. Key difference being that Atkinson has a different stroke length on induction than on expansion. In a modern hybrid, they emulate/approximate this by by building a high compression engine (with equal stroke lengths), then decompressing it back down by keeping the inlet valve open part of the way through the compression stroke. The piston pushes out some of the inlet charge, so your statically calculated compression ratio (cylinder capacity vs chamber capacity) is not the same as your dynamically realised compression ratio.

Hybrids can also safely run higher compression ratio's because the computer has better control over the engine loads, load being a key inducer of detonation. Detonation (low-speed) typically occurs when you demand big torque at low RPM. An Atkinson engine has low/no torque at low RPM (hence the requirement for electric assist which is where the term "Hybrid" comes from), and the computer strictly controls the throttle position and load on the engine at all times. Any shortfall in load delivered by the engine is delivered by the electric motor instead. Unlike a non-hybrid where the petrol engine delivers all the torque, and in a manual (and to a lesser degree, automatics) where the ape behind the wheel can mash the accelerator in any gear, at any speed, at any RPM, inducing knock.

Once you throw EGR, direct injection and lean burn into the mix, compression ratio to octane rating gets more flexible and less absolute. Again, features the OP's car probably doesn't have.

mudguard:

Short of putting it on a dyno with 91 to 98 in it or running tanks of each to work out the mileage I'd go with what the manufacturer recommends.

Of course, read and obey the manual when available. But it wasn't available and the OP wanted a central repository of this data. If in doubt, too high octane will not harm the engine, but too low can, and will in older, dumber cars. Also some OEM's give a range e.g. 91 or 95. In these cases, the lower octane, won't always give you the best economy (km per $) nor the best driving experience (smoother running, better acceleration, lower RPM etc).

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