Why do people buy high octane petrol?

[Sindri]

No.

I put 98 in the Legacy.

Bs, regardless of what it is tuned on the engine can adjust accordingly to a different octane level.

 

[Fr0dders]

Bs, regardless of what it is tuned on the engine can adjust accordingly to a different octane level.

Only to a certain extent.

Importers advise that Jap Imports be remapped to UK fuel as you can never be 100 % sure that the car is going to run fine on 95 RON fuel and retard the ignition sufficiently not to cause problems.

Generally speaking, if your car manufacturer says to run your car on a specific petrol, do so.

 

[Sindri]

Only to a certain extent.

Importers advise that Jap Imports be remapped to UK fuel as you can never be 100 % sure that the car is going to run fine on 95 RON fuel and retard the ignition sufficiently not to cause problems.

Generally speaking, if your car manufacturer says to run your car on a specific petrol, do so.

I never said it would run perfectly, magnolia stated that using RON 98 was pointless on a car typically designed for 95.

It is extremely unlikely you would find a modern car that didn't receive any benefit from using 98 over 95.

 

[[FnG]magnolia]

So, erm, if an engine is tuned for 95 RON, does using 98 RON have any point ?

No.

I put 98 in the Legacy.

Bs, regardless of what it is tuned on the engine can adjust accordingly to a different octane level.

Whether an engine can 'adjust' and whether there is any point are two different things, aren't they? I don't think snowdog will see any performance increase in his volvo (is he still in that?) running 98 over 95, if, as he says, it was tuned for 95.

Keen to hear your thoughts on what 'adjust' means given the nature of the thread.

 

[Kenai]

I use super unleaded because as far as I am aware, the 1.8T has an adaptive ECU that will advance ignition timing to take advantage of it and when using it, I find the car revs more smoothly in the middle of the rev range too.

 

[Sin_Chase]

The best Octane I can get at the pump, always.

Locally that is either 97 or 98. It works out a little bit more expensive but not so much so I think twice about picking up the SUL pump.

 

[Clarkey]

I hear this story a lot about ECU's that will actively tune themselves up and I simply don't believe it. Can any actual ECU mappers/experts confirm it? If this were true then what the heck is the point in remaps.
I'm a bit old school but the way I know it an ECU generally has a standard map and a knock map for if it senses knock, and is able to fine tine the AFR based on lambda readings.

 

[NathWraith]

95 RON is fine with the Cupra but in small brackets it mentions performance will be slighlty decreased over the standard 180PS.

So super unleaded it is!

 

[[FnG]magnolia]

I hear this story a lot about ECU's that will actively tune themselves up and I simply don't believe it. Can any actual ECU mappers/experts confirm it? If this were true then what the heck is the point in remaps.

I think I meant to make this point but you used better words and formed a better argument so let's pretend that I said what you said and everyone can ignore my post two or three above

 

[ScoobyDoo69]

They don't tune themselves up, they have set parameters, and if you can get into those parameters due to better fuel then you will benefit. All done very quickly via the knock sensor, throttle position sensor etc.

It's just like if you hammer your newish car it will feel faster, because the ECU is made to be on the WOT (wide open throttle) parameter, it can then continually go up the stages in the ECU based on the fuel in the tank. An ECU will have so many varying parameters for WOT based on all different temperature sensor readings. Air intake temperature etc.

When you just tootle in your car all the time it will sit in the lower ignition timing zones and less fuel in zones so it will feel slower until you've booted it for a bit.

 

[Kenai]

No one is claiming that using VPower is going to get you 50BHP, or that an ECU will increase the boost pressure of a turbo because it senses 98RON instead of 95RON (which is mostly what produces the massive increases on a 1.8T remap for example, increased boost).

What I believe is the case with the Bosch ME7.5 on the 1.8T is that it will continually try and advance ignition timing as much as it can until it senses knocking, better fuel means it can advance this more and more before that happens. Unless i'm wrong, the more advanced the ignition is, the more power the engine is making, it won't be massive or anything that does the job of a remap but that doesn't mean it isn't happening.

Being able to adapt to better fuel is not 'tuning itself up'.

 

[ScoobyDoo69]

I think one of the best ways of explaining it is with a forced induction car.

Imagine it's cold, we all know that colder air means more air as it is more dense. If you are running say a 97 Octane fuel, and are booting it in the cold weather. Due to their being more air then say at a 20deg C day, the car either needs more fuel or less ignition timing. Most of the time the easiest option would be the less ingition.

Bring V-Power into the equation, and now the ECU sees the extra air, and can hear via the knock sensor that there is less det due to the better fuel. Therefore the car can continue to have the same ingition timing, with the extra air, and now the car can add a bit more fuel as it's all well within it's safety with the better fuel in the tank.

Again remember that this is all done within SET parameters, the car does not go beyond these. For example if it is so cold that the air coming in is that much thicker than the car can deal with, some turbo charged cars overboost and the ECU reigns things in with limp mode, where the boost and ignition etc are limited. Or it just cranks the wastegate duty as far down as possible to reduce boost..

ECUs are complex these days, but lets just say better fuel = better running

 

[Matt82]

What I believe is the case with the Bosch ME7.5 on the 1.8T is that it will continually try and advance ignition timing as much as it can until it senses knocking, better fuel means it can advance this more and more before that happens. Unless i'm wrong, the more advanced the ignition is, the more power the engine is making, it won't be massive or anything that does the job of a remap but that doesn't mean it isn't happening.

the case with the Bosch ME7.5 on the 1.8T is that it will continually try and advance ignition timing as much as it can until it senses knocking,

it will adviance the timing as far as is dictated by the map for the given throttle/temperature/load/airflow situation

it will advance to that point and if knock is detetected, the timing is retarded momentarily, so timing will be (Map figure - X*)

if you keep your foot buried, it will actually try to revert back to the map figure, but if knock occurs, it retards again.

with lower octane that threshold occurs sooner. on the standard map, the threshold probably never occurs

 

[LeeUK]

I fill up with V-Power because it makes me look cool at the filling station. Also I don't watch the meter while filling up either. I can afford it.

 

[Gaijin]

As said by others, because my car is mapped for V-Power. Running 95 RON WILL cause it to det.

I don't even like running other SUL's in it and have only done so twice in the 3 or so years i've had it, and even then only enough to get me to a Shell garage.

 

[markweatherill]

Yup, even down to 91!

Sounds bad but 'their' octane numbers are measured differently.

 

[MOOGLEYS]

My subaru drove horrid on 95 fuel. Only did it once as an emergency but it was a very noticeable difference.

 

[bigjimmyauk]

When it was Optimax it was 98 now it's Vpower it's 99.

V power at my local garage says 97Ron? and tesco is 99Ron

 

[Jonnycoupe]

I think one of the best ways of explaining it is with a forced induction car.

Imagine it's cold, we all know that colder air means more air as it is more dense. If you are running say a 97 Octane fuel, and are booting it in the cold weather. Due to their being more air then say at a 20deg C day, the car either needs more fuel or less ignition timing. Most of the time the easiest option would be the less ingition.

Bring V-Power into the equation, and now the ECU sees the extra air, and can hear via the knock sensor that there is less det due to the better fuel. Therefore the car can continue to have the same ingition timing, with the extra air, and now the car can add a bit more fuel as it's all well within it's safety with the better fuel in the tank.

Again remember that this is all done within SET parameters, the car does not go beyond these. For example if it is so cold that the air coming in is that much thicker than the car can deal with, some turbo charged cars overboost and the ECU reigns things in with limp mode, where the boost and ignition etc are limited. Or it just cranks the wastegate duty as far down as possible to reduce boost..

ECUs are complex these days, but lets just say better fuel = better running

Good job you started with the word imagine isnt it

A ECU calibration works nothing of the sort, it will have IAT (Inlet Air Temp) enrichment otherwise you have a lean mixture as air fuel ratio is governed by the mass ratio of the two parts... fuel & air. It doesn't use a knock sensor like you describe either.

Timing is all about pushing a child on a swing analogy. Pushing early, or advancing ignition as much as possible, wont get you the best results.

Wastegates are controlled by pneumatic - mechanical actuators in most application with boost control done by ECU controlled PWM bleed valves. There isnt a logic system as its a pretty simple feedback loop. Overboost like you describe is due to a poorly design system or one thats operating masssively outside its application envelope.

 

[ramirez]

my s2000 clearly says use 97 ron.... so i do.

its only a couple of quid a week extra anyway, big deal.