Fuel octane ratings and Engine damage

[HenryDorsetCase]

https://www.stuff.co.nz/motoring/115...mpensation-bid


I didnt think the 4% (or so) difference in octane rating would make enough of a difference to lunch a motor - especially a modern motor with knock sensors and so forth.

My understanding of detonation is that the fuel spontaneously combusts in pockets in the combustion chamber before the main fuel charge is ignited by the spark plug.... causing uncontrolled pressure and thus causing damage to an engine.

Fascinated if anyone has any insight.... also whether I should be running my street bikes on 95 - I've always used 91 because it seems to run OK on it.....

[BadSarah]

It was my understanding that a vehicle designed for 95 would run poorly and be less efficient on 91. I was also given to believe that higher octane can damage parts of fuel systems, particularly if it has a higher level of ethanol in the fuel mix.

Sent from my SM-G955F using Tapatalk

[SaferRides]

Not a good idea to run a Euro car on NZ 95, let alone 91, but the knock sensor should have prevented any damage.

No responsible dealer should be selling used import VW's anyway.

[george formby]

Not a good idea to run a Euro car on NZ 95, let alone 91, but the knock sensor should have prevented any damage.

No responsible dealer should be selling used import VW's anyway.

Why do you say that?

[onearmedbandit]

I've had first hand experience with many of the aforementioned vehicles, and continued use of 91 will kill these engines. Especially the Highline model with the 1.4TSi twin-charge engine (super and turbocharged). I'm not in the slightest surprised her engine was damaged.

[onearmedbandit]

No responsible dealer should be selling used import VW's anyway.

Ignorance 101.

[Laava]

Not a good idea to run a Euro car on NZ 95, let alone 91, but the knock sensor should have prevented any damage.

No responsible dealer should be selling used import VW's anyway.

So what should you run it on? Given that 98 is not commonly available.

[onearmedbandit]

So what should you run it on? Given that 98 is not commonly available.

95 is perfectly fine. From someone that has sold in excess of 400 Golf models plus numerous other Euro’s, and who also runs a modified GTi that puts out 150% of its original power on 95 all day long.

[Laava]

That's what I would have thought...

[pritch]

My import is supposed to be run on 100 Octane but...

The manuals for my bikes recommended 95, so 95 it was. The Triumph manual specifies 95RON and I believe that's what we have.

Used to put 95 in the moped too, didn't want any less power than the poor little thing was capable of producing.

[HenryDorsetCase]

My import is supposed to be run on 100 Octane but...

The manuals for my bikes recommended 95, so 95 it was. The Triumph manual specifies 95RON and I believe that's what we have.

Used to put 95 in the moped too, didn't want any less power than the poor little thing was capable of producing.

Errrrrr. Read the manual you say? Shit, I never thought of that. Fuck.

wonder if my rings and pistons are crumbling as we speak?

[onearmedbandit]

My import is supposed to be run on 100 Octane but...

.

What car is that?

[Temporary-Kiwi]

octane ratings are an indicator of what you get out of the pump, I once talked to a tanker driver, he said that a delivery could be diluted up to 6% by an alternate fuel.
so that 91oct might have a few % of diesel in it !
I've had detonation troubles caused by various things in modified engines, mostly in my xr650r, once I went over 12:1 comp ratio it won't run on 91oct without protesting
, I went around the south island on it , the mtr in super mortard eng spec , I fitted a lead adding device , it ran ok on 95 Oct, but still didn't like 91.
most bikes sold in nz, will happily run on 91oct when std, but big-bore hi-comp singles are susceptible more than most

[Honest Andy]

Ignorance 101.

The real ignorance was the driver who kept running a car that must have been pinking like hell!

[OddDuck]

https://www.stuff.co.nz/motoring/115...mpensation-bid


I didnt think the 4% (or so) difference in octane rating would make enough of a difference to lunch a motor - especially a modern motor with knock sensors and so forth.

My understanding of detonation is that the fuel spontaneously combusts in pockets in the combustion chamber before the main fuel charge is ignited by the spark plug.... causing uncontrolled pressure and thus causing damage to an engine.

Fascinated if anyone has any insight.... also whether I should be running my street bikes on 95 - I've always used 91 because it seems to run OK on it.....

Octane rating is a weird beast. Have a look at the wiki page: https://en.wikipedia.org/wiki/Octane_rating

Basically there are two reference fuels and a specified test engine (of unusual geometry) which set the scale. One fuel has a knock rating of 0, the other a knock rating of 100 (by definition), it isn't linked to any absolute values of pressure, temperature etc. It's an arbitrary scale, but it's repeatable and so it's fit for purpose.

Detonation: yes, pockets of the fuel go bang in advance of the flame front, leading to a massive rise in pressure and heat in the cylinder since the detonation happens so quickly. Really bad detonation will be the main charge going off before the spark bubble has a chance to propagate.

From reading the Stuff article, it sounds like they were going cheap to save those precious bucks... yeah didn't work very well I guess. On that note, apparently the hypermilers (people who keep notebooks of $ vs km) have been finding that for a given octane rating, it's actually the most expensive fuel per litre that gives you the most km's per buck... something to do with the calorific value of the fuel blend. Not all 95 is equal.