Is too high an octane level bad?

[Rowland]

Hi folks,

I've recently used Millers 'Octane Plus' coupled with Shell Optimax to bring the octane rating up to 99.4 RON.
I have a Japanese Mines aftermarket ECU which I'm told will have been set up to run on 100 RON fuel as used in Japan.
Now, Millers have brought out a new product called 'CVL Turbo' which when coupled with Optimax gives 101.4 RON.

Are there any side effects to running a mk2 Turbo at this kind of octane level?

Cheers

PS. I quote these octane levels from Millers themselves and believe they're correct.

[raptor95GTS]

can't see how running too high an octane is bad since these cars are setup to run 100 anyway.

I guess that millers stuff raises the octance by 8 points then?

[Hedgehog Dodger]

can't see how running too high an octane is bad since these cars are setup to run 100 anyway.

I guess that millers stuff raises the octance by 8 points then?

No, something like 3.2 Octane points with Optimax.

[Rowland]

can't see how running too high an octane is bad since these cars are setup to run 100 anyway.

Hmmm...maybe you've missed my point.
'Is running a 3SGTE on fuel over 100 RON detrimental to the running of the engine?'

Cheers.

[jonno]

From what I remember from university the octane rating is simply a measurement of how much the fuel can be compressed before it ignites. In an engine, if the fuel ignited due to compression rather than the ignition spark, det would occur. So, the higher the octane the higher the compression ratio could be, or the more boost you could run. I dont recall any issues with fuel being too high an octane value - although I am probably wrong

It also is obvious that cars that are meant to run on 95 octane wont gain much benefit from running 98 octane fuel - unless the ECU is able to advance the ignition or run more boost to take advantage of it.

Neil.

[raptor95GTS]

can't see how running too high an octane is bad since these cars are setup to run 100 anyway.

Hmmm...maybe you've missed my point.
'Is running a 3SGTE on fuel over 100 RON detrimental to the running of the engine?'

Cheers.

nope I didn't miss the point - i said can't see how running too high an octane is bad since these cars are setup to run 100 anyway.

[raptor95GTS]

can't see how running too high an octane is bad since these cars are setup to run 100 anyway.

I guess that millers stuff raises the octance by 8 points then?

No, something like 3.2 Octane points with Optimax.

so that would take it from 98.6 to 98.92. Hardly worth the cash and effort

[Lauren]

can't see how running too high an octane is bad since these cars are setup to run 100 anyway.

Hmmm...maybe you've missed my point.
'Is running a 3SGTE on fuel over 100 RON detrimental to the running of the engine?'

Cheers.

Just to answer your question (!) nope it won't do any harm at all and is generally a good thing, though it could prove a bit expensive if you keep buying octane booster.

[Shmed]

can't see how running too high an octane is bad since these cars are setup to run 100 anyway.

I guess that millers stuff raises the octance by 8 points then?

No, something like 3.2 Octane points with Optimax.

so that would take it from 98.6 to 98.92. Hardly worth the cash and effort

Erm, correct me if i'm missing something, but I am of the understanding that 98.6+3.2=101.8
98.6+0.32=98.92

[raptor95GTS]

No, something like 3.2 Octane points with Optimax.

so that would take it from 98.6 to 98.92. Hardly worth the cash and effort

Erm, correct me if i'm missing something, but I am of the understanding that 98.6+3.2=101.8
98.6+0.32=98.92

yes actually you are

1 octance point is one tenth of a RON so adding 1 point to any fuel is actually adding 0.1 of a RON

So therefore if you add 3.2 points to shell optimax at 98.6 RON then you get

98.6 + 0.32 = 98.92

if however you raised it by 3 RON then it would be
98.6 + 3.0 = 101.6

Be careful out there

[Shmed]

Thanks, I knew you were quite knowledgable (from the old forums) so had to confirm that this wasn't a typo or anything.

Hey, every days a school day!!

[stevecordiner]

In an ideal world you want to use the lowest octane you can without suffering any negative effects on performance or engine safety.

Using too higher octane can cause its own problems - e.g. you sling 120 octane fuel into your car you'll fine it doesnt like it too much lol!

[SimonPearse]

In an ideal world you want to use the lowest octane you can without suffering any negative effects on performance or engine safety.

Using too higher octane can cause its own problems - e.g. you sling 120 octane fuel into your car you'll fine it doesnt like it too much lol!

whywon't it like it?

[gtschris.com]

In an ideal world you want to use the lowest octane you can without suffering any negative effects on performance or engine safety.

Using too higher octane can cause its own problems - e.g. you sling 120 octane fuel into your car you'll fine it doesnt like it too much lol!

whywon't it like it?

higher the octane the hard it is to burn, wonder what diesel is?

[SimonPearse]

are you sure about that? I know that aero engines using special high-octane rating fuels tend to use dual spark ignition due to the dificulty of initiating combustion, but I thought that the difficulty was overwhelmingly caused by the high compression (which requires the high octane fuel) rather than by the properties of the fuel itself.
I may be wrong about this but I think that whilst higher octane fuels do require a greater spark temperature for ignition the effect is almost utterly inconsequential.
Diesel fuel, of course has a LOW resistance to compression-ignition, and has an extremely low octane rating

[BenF]

In an ideal world you want to use the lowest octane you can without suffering any negative effects on performance or engine safety.

Using too higher octane can cause its own problems - e.g. you sling 120 octane fuel into your car you'll fine it doesnt like it too much lol!

whywon't it like it?

Higher octane fuels (like 130 Octane) tend to burn really slowly, as well as having good detonation resistance. This means the fuel is still burning as it leaves the cylinder, travels around the turbo and out the exhaust.

The turbo won't appriciate getting too hot

[SimonPearse]

that is true, but in a spark-ignition petrol engine it's normal for the burn to be completed within a few degrees of tdc (unfortunately!) so that I would have thought that even without advancing the ignition timing there would be little liklihood of a significant increase in burning residuals reaching the turbo?

[stevecordiner]

Your car would need to be retuned for the very high octane stuff. For instance theres a chap in the US who tuned his car to 110 octane and uses 114 at the drag way for safety. If he trys 116 his car runs badly and performance suffers.

RON and overall octane is different. Optimax is around 93-94 octane (RON+MON/2), so you'll see something like 120 octane is a massive jump considering something like normal 95 RON unleaded is around 91 octane and if I put that in my car when its tuned for optimax it runs much slower

[gtschris.com]

are you sure about that? I know that aero engines using special high-octane rating fuels tend to use dual spark ignition due to the dificulty of initiating combustion, but I thought that the difficulty was overwhelmingly caused by the high compression (which requires the high octane fuel) rather than by the properties of the fuel itself.
I may be wrong about this but I think that whilst higher octane fuels do require a greater spark temperature for ignition the effect is almost utterly inconsequential.
Diesel fuel, of course has a LOW resistance to compression-ignition, and has an extremely low octane rating

Yup, sure i am right.

You have answered your own question, high compression engine would detonate badly if you used 95 ron fuel, so the 115 ron aero fuel is harder to burn thus with stands the higher compression without burning until the spark triggers internal combustion.

Diesel has a cetane rating, it was kinda a throw away comment, diesel is hard to burn a Vauxhall 1.5D engine runs a 23:1 compression ratio if i rember correct.