LSherratt

iTrader: (1)

Really dumb question I know and I'm going to sound stupid but what is the actual reason of why performance cars need 99 or higher ron fuel?

I always run my car on Tesco Momentum 99 and won't use anything else but my girlfriend has asked me a few times "why don't you put normal unleaded in it?" and all I can say is "because it's just better the engine and less likely for it to go wrong".

What is the technical answer to why performance cars need 99 ron fuel?

WRXghost

Cleans your engine as you drive. The cleaning components are designed to prevent the build up of power-robbing deposits and to help remove those which may have been left behind by other fuels e.g super market fuels
I use V-Power tho not to shur what momentum is like .

XPCobra

To minimise the risk of pre-detonation

JGlanzaV

iTrader: (3)

Wronggggg.....


Albeit might be a contributing factor, the reason to use 99 fuel is to prevent detonation and stop your engine going pop.

You can have it mapped for lower ron fuel but will sacrifice power etc as it will have to be mapped with less ignition timing etc

WRXghost

that's what I mean lol
at least I learned something new

Lunchmoney

From http://en.wikipedia.org/wiki/Octane_ratingMy bolds

Octane rating or octane number is a standard measure of the performance of a motor or aviation fuel. The higher the octane number, the more compression the fuel can withstand before detonating (igniting). In broad terms, fuels with a higher octane rating are used in high performance petrol engines that require higher compression ratios. In contrast, fuels with lower octane numbers (but higher cetane numbers) are ideal for diesel engines, because diesel engines (also referred to as compression-ignition engines) do not compress the fuel but rather compress only air and then inject the fuel into the air heated up by compression, whereas petrol engines (also referred to as gasoline engines) rely on ignition of air and fuel compressed together as a mixture without ignition, which is then ignited at the end of the compression stroke using spark plugs. Therefore, high compressibility of the fuel matters mainly for petrol engines. Use of petrol (gasoline) with lower octane numbers may lead to the problem of engine knocking.

JGlanzaV

iTrader: (3)

RS_Matt

99 is said to be more efficient, I'm not sure if it has cooling properties.

DJB3

It allows more ignition advance which ultimately equates to more power and better efficiency so if you then add standard RON fuel, to protect engine ECU will immediately retard ignition timing dropping power output.

riiidaa

iTrader: (2)

to avoid det.

hodgy0_2

simply put it has a higher calorific value

1 ltr of super has more "energy" than 95ron

LSherratt

iTrader: (1)

Ok thanks, I've just told her this:

"In performance car engines such as my Subaru, the engine requires higher compression ratios in order for it to run effectively and properly to give maximum power safely. 99 ron fuel (such as Tesco Momentum or Shell V-Power) can withstand more compression before detonating (igniting). Constantly using lower ron fuel such as standard unleaded can cause major damage to the engine because it can’t withstand the higher compression ratios."

Hopefully that will suffice and is good enough of an answer!

ronjeramy

iTrader: (1)

The higher Ron the cooler the engine runs, hence why you can squeeze more power out. The old JDM vs UK thing, they have 100ron fuel in Japan as apposed to our 97-99 Ron super hence they have more power out of the box.

joz8968

iTrader: (13)

Or you could have just simply left her with:

"There, there, don't worry your pretty little head about it."

LuckyWelshchap

For 'octane, RON' or whatever read 'combustability'.

The more explosive the fuel, the greater the power of the ignition, and hence the greater the force delivered to the crank, and hence ultimately to the drive. Timing is of course very important (no point in a massive force in one cylinder and a weak one in another).

Modern engines (and timing) are controlled by computer ie ECU and this 'controls the flow' ie. regulates the explosion (as in detonation of the fuel/air mixture) so as to ensure the most effective cycle of pushing the crank around ie. not so much as powerful as possible but as efficiently as possible.

In effect each cylinder/piston/con-rod's explosion has to be synchronised so that the 'chain reaction' has the most effective result. A bit like a rugby scrum. tug-of-war etc. All (4) cylinders must work in harness in order to produce the goods.

The higher the RON/Octane, the more explosive the fuel, and therefore the more explosive the power that each cylinder explosion can drive the con-rod/turn the crank/power the wheels.

The ECU is programmed to optimise this effect.

Program it for eg. 99 RON and it will tell each cylinder to spark on the basis of 'the team (ie all 4) maximising the turning effect on the crank.

Put 97 in it and it will still apply 'the rules' but the obvious problem is that the power of combustion will not be as expected, and therefore the effect will be less.
Computers these days should be clever and the ECU will suss that the power of combustion is not what should be, and should delay detonation until what it thinks is sufficient fuel is in the cylinder to produce the desired/required combustive force.
Unfortunately the opposite is true. The ECU carries on telling the cylinders to fire at the 'right' time but the mixture does not produce the expected power. If it waited a little longer there would be enough of a mixture to do as intended.
If you don't wait long enough of course you are premature - which is the 'pre' of 'predetonation.

ALi-B

iTrader: (1)

Actually it's the reverse, ethanol as well as other additives Used to increase RON values tend to have a lower overall calorific value than the base petrol.

My last impreza (my97 turbo 2000) always ran 95ron. Clearly printed in the manual (inside and the back cover). Never had an issue.

Fuel flap said gasoline. Which is obviously incorrect....we call it petroleum

Gear Head

iTrader: (2)

Plus a turbo car actually runs lower compression ratios.

Seriously, the amount of bullsh!t on this thread is hilarious. If you don't know, don't guess!
All the info is available on the internet you lazy little gits!

300gnspitzer

LuckyWelshchap, what a load of tosh.

LSherratt

iTrader: (1)

So no one actually knows then?

Gear Head

iTrader: (2)

A higher Ron fuel means that it will sustain a controlled combustion for longer. It helps avoid 'pinking' or pre-detonation. I.E. the fuel is less likely to ignite before it is required.

Gear Head

iTrader: (2)

Because the combustion chamber temps increase when you start driving the car hard. So much so that a lower Ron fuel can ignite before a spark is given which is very bad for the engine for obvious reasons.

Gear Head

iTrader: (2)

Put it this way:

If you use 95 Ron fuel in an Impreza turbo and then drive a dick, you will be very lucky if your engine stays in one piece.

LuckyWelshchap

What a lack of understanding.

Why do you think an engine goes bang?
One cylinder ignites out of sequence (might be millisecs but it's still out of sequence) and its part of the crank isn't at its optimum turning point, so the conrod gets stressed. Worst case scenario the piston can't turn the crank (so far out of position as to be like a brick wall) and the conrod's unable to stay straight, bends, snaps and goes through the block.

See if you can find 8 rugby forwards to push out of sync and watch the mess that follows. (Cardiff, last 6 Nations game is a good example ).

LuckyWelshchap

^^^^^

And as already said, the mixture will be denser because more fuel can be used, so the explosive power of ignition is greater, imparting more turning force on the crank and hence greater power.

Gear Head

iTrader: (2)

Not more fuel, more air.

LuckyWelshchap

My apols, I should have said what I meant - a more combustive mixture (because of more air/oxygen).

It will be denser because although the proportions might be the same it will occupy less space, being (able to be) compressed more, because of the less risk of it pre-deting.

ALi-B

iTrader: (1)

Apart from hodgy is wrong...98+ RON almost always has LESS energy due to the additives used having lower calorific values.

Making full use of that energy is a whole different ball game...Higher Ron requires a more robust ignition system. Typically, the higher the RON the more difficult it is to ignite. This is why LPG systems always show up duff plugs/leads/coilpacks by misfiring or putting out more hydrocarbons out the tailpipe (de-cat)....but always run better on lower RON petrol. Add to that a leaner mixture can give more potent combustion (i.e more power), but is also more difficult to ignite.

If your car can't ignite all of the fuel, energy is wasted; RON is irrelevant, unless its too high. AFR is a key point here, but ignition timing, injector atomisation, cam timing, combustion pressure, etc. all have a part to play.

Low RON fuel typically burns faster. Higher RON fuel typically burns slower. Therefore the ignition point has to be timed to suit; An engine will lose power and efficiency by igniting the fuel too late (over-retarded) where it is ignited too far past top dead center (TDC). We all to often hear about the over-advance of ignition leading to uncontrolled combustion, which is bad. Over-retarded is safe, but causes power loss.


AFR is another interesting thing...people say if you run leaner than 14.7:1 AFR a car will det and die...BOLLOCKS. Why? I own a run a car with a lean-burn engine with a much higher compression than your average Subaru and the most basic of basic ignition/fueling system, and guess what? It doesn't det. It'll happily wreck a ignition coil due to the extra stress its under, but you can run as lean as you like and it just refuses to det. BUT its not a Subaru, so it has cleverer combustion chambers and doesn't have chocolate pistons...so it runs hotter; not an issue if the cooling system is up to job (a noted failing point).


Anyway, this just goes in circles: Maintain AFR at stoic, and as long as you don't have glowing deposits as a source of ignition, you won't get det. Over-enrich, you won't get det. Over-advance, you won't get det. Put in a higher than normal RON, you won't get det.

Its surmountable to the same goal: If the engine has the correct ignition/fueling/compression and nothing is wrong with it, It'll be OK. BUT if there is something wrong with it, you fix it....For example; putting in a higher RON fuel wrong won't fix a under-reading MAF or a engine running higher than normal boost pressure. In the case of my lean burn engine its the cooling system - make sure its doing its job. If it overheats I'm looking at dropped valve seats, so I make sure the cooling system is doing its job...I don't just bung in 99RON for the sakes of it when its tuned for 97RON.

And that's a big point rarely uttered on Scoobynet...older Subarus have 3yr/4yr coolant change intervals.....yet so often I hear arguments about fuel, yet so often I see people with Subarus that don't bother changing the coolant and very rarely do I hear or see any arguments about the advantages/disadvantages of using a silicate/phosphate/OAT coolant...or mixing them after a partial drain (can't fully drain a Subaru). Bearing in mind its this stuff that keep the cylinder heads cool...and the only reason we have coolant in the cylinder heads is to help prevent the det....

I know coolant is a big issue on the control of combustion temps, because historically its always has been - its why coolant is in there....and bad coolant has historically killed many cars and given them bad reputations for dying young....yet on Scoobynet...its rarely even mentioned.... we just argue about the petrol.....why so?

ALi-B

iTrader: (1)

LOL, yep, the bigger the number the better it is

110RON fuel
20w-80 oil

....and the radio volume set on 50