91, 95, 95e or 98 RON...:-( Help )

[asdf1234]

Firstly I'm referring to WP and WQ Fiestas, may not be right for newer models. Fuel grade is all about 'pinging'. Without getting too technical, the Fiesta has a slightly higher compression ratio than many engines, 11:0 opposed to many 10:1 for similar cars. Higher grade RON 95/98 is therefore a better option to reduce ping in these engines specifically. Having said that modern day cars have electronics and what not that means it will run on RON 91 petrol just fine. Personally I have experimented with all 3 grades. The premium grades are definitely noticeably quiter and smoother. In terms of price wise, you definitely get a reduction in fuel consumption but the price is obviously higher. The math works out that it comes at about a 5-10% premium ie. if RON 91 cost you $10 per 100km than RON 95/98 cost you about $10.50-$11 per 100km. In terms of performance it is too hard to tell if it's a real power gain or just placebo effect. Personally I stick with RON 95/98 because I would believe its better for the engine and the final price difference is so small.

[asdf1234]

Originally Posted by fiestaz

Really??? What model is it? My 04 Fiesta runs good on 95, and Great on 98. Tried 91 once, ran terribly and was awful, never have tried e10. Sounds like a different issue to me.

^+1

Good summary of my experiences.

[blatchie]

Thanks for that. Another issue is a dead spot between 3 and 4 thousand revs between gears.

[somers181]

I have been running E10 in my WT auto since day 1 and car has now travelled 11,000 kms and it has not missed a beat, it drives great in peak hour and open road. When i had my initial "adjustment/checks" at Ford i asked about the different type of fuels to use as the filler flap says its safe for E20, they said if you are running E10 the computer system makes ajustments for different fuels and try and stick to the one type, not to use 98 1 in ten fills etc.........

[Caydus]

The Wikipedia article should explain it the best.

Originally Posted by Wikipedia

The higher the octane number, the less likely is the fuel to ignite prematurely in the engine's cycle and cause the engine damage.

These are the few points I understand about octane rating

* The higher the octane rating, the harder it is for petrol to spontaneously ignite under compression, which if it does, causes knocking, leading to loss of power and engine damage
* All petrol, whether it's 91, 95 or 98 RON have the same energy per unit volume
* If petrol is mixed with ethanol, which has much lower energy per unit volume, the ethanol acts as an octane booster and also lowers the average energy per unit volume of the final product (E10/E20/etc)

A lower energy per unit volume potentially leads to lower fuel economy assuming efficiency of extracting said energy is constant.

The Fiesta's engine has a higher compression ratio than most engines of it's class, 11 as opposed to 10, resulting in a higher tendency to knock, or ping when using lower RON fuels.

The higher a compression ratio of an engine is, the harder the air/fuel mixture is squeezed before it's ignited by the spark plug.

Now to the point I'm least sure about: Higher compression ratios lead to higher efficiency when extracting energy out of the fuel, resulting in higher fuel economy and/or greater power, if the fuel doesn't pre-ignite first.. Which means a higher RON rating of fuel is required.


So bottom line to take away from all this:

If your engine doesn't ping/knock on that particular RON of fuel, you don't need to go higher as you will not get any gains from it.
I'm pretty sure this is how it works, until they introduce computer controlled variable compression ratio mechanisms into engines, which may never happen...

E10 will always give poorer fuel economy, but since the amount of ethanol they blend in is variable (up to 10% they say), your mileage will vary.


I'm by no means an expert and only know this by reading random comments people throw out there, so please correct me if I'm wrong.


Personally, I only use 95RON in my WT Fiesta. I tried 98 for a few tanks, got zero gains and 91 made it ping slightly under certain conditions.

[GoesLikeAZetec]

we use 98 and it stopped the pinging in hot weather and we get slightly better economy than the 91 we originally used..

[Dustproof]

Originally Posted by Caydus

If your engine doesn't ping/knock on that particular RON of fuel, you don't need to go higher as you will not get any gains from it.
I'm pretty sure this is how it works, until they introduce computer controlled variable compression ratio mechanisms into engines, which may never happen...

E10 will always give poorer fuel economy, but since the amount of ethanol they blend in is variable (up to 10% they say), your mileage will vary.


I'm by no means an expert and only know this by reading random comments people throw out there, so please correct me if I'm wrong.


Personally, I only use 95RON in my WT Fiesta. I tried 98 for a few tanks, got zero gains and 91 made it ping slightly under certain conditions.

That is a very good explanation of the way Octane works, well written. Now to work on why higher Octane works better in some cars.

Modern cars have a closed loop engine management, this changes the ignition advance as well as the fuel mixtures. Part of this system is a censor in the exhaust that measures the Oxygen levels as the gasses flow, it also has a knock sensor to detect pinging, well apart from all the other sensors such as water temp etc.

We must understand that the fuel mapping is made to be lean because of fuel economy and antipollution systems. Lean mixtures will pre-ignite in a hot engine for many reasons including an exposed thread on Spark Plugs.

Taking this information, combine it with a high compression engine will cause Pinging on low octane fuel. The problem with Ethanol is the fact we use only 10%, in fact you can get more power from 100% Ethanol, basically because the higher the Octane the more advance can be used along with a much higher compression ratio, unfortunately our engines are too limited in the tune to handle this fuel because. If you watch V8 Supercars, they use E85 because of this reason.

Now, with the High Octane fuels such as 98, our engines will self tune. All the sensors tell the ECU that the engine is able to run better so it allows more advance and better fuel/air mix to make the engine run better. This will not always translate into a power increase we can feel although it is there, we usually use up this extra power without realizing it with the right foot.

In Australia, we have the better fuel than the US, the best they have is 95 although in saying that it depends on the state your in. If we use the higher octane fuel, our cars run better and will last longer, especially because the oil companies use cleaners etc to keep the car running at it's best in the higher octane fuels.

Whether it will give better fuel economy, not really is the answer BUT your car will benefit from it. Ethanol will be a fuel of the future unless someone comes up with something better, Holden has already a E85 car on sale, it has a special tune that allows the use of this fuel, the problem is they want it to run of normal fuel as well, this stuffs up the power output. A car needs to be built to run on ethanol, it will then never run on petrol again if in this state of tune.

Now for my experience, I use 98 in my motorcycle. Immediately I started using it, I got over 100km's from the higher octane fuel. The engine runs better and less like a chaff cutter, more comfortable and generally better to ride. I will always use 98 although not Shell, this is a whole other story.

I hope this helps.
Dusty

[small_ford]

I have the 1.6 engine in a Focus, minus the VVT but otherwise same as Fiesta engine. It done almost 150000km without problem. I have always used 95RON petrol, it is specc'd for it. The 1.6 Sigma engine has a knock sensor so 91 will not destroy the engine, but I suspect with 11.1 CR 95 is preferable.

Re warm up - don't idle the engine to warm it, just a waste of petrol. Just be gentle on the engine try to stay at 3000rpm max with gentle acceleration until it has wamed up. The heater will tell you when engine is really warm.

Finally change the oil/filter every 10000km using 5/30 and keep the other maintenance items to Ford spec and you would be very unlucky to have major problems.

[josem]

Originally Posted by small_ford

I The 1.6 Sigma engine has a knock sensor so 91 will not destroy the engine, but I suspect with 11.1 CR 95 is preferable.

So for the 1.6 LW Focus, manual says 95RON preferable but e10 acceptable. Is regular e10 which is around 91RON safe or should I stick to straight unleaded 95 or 98 RON ? The 1.6 sigma engine is similar to ST Fiesta and the fiesta does not require 95RON.

[martinijosh]

Manual for our new WT Fiesta says 91 suitable, but 95 recommended.

Originally Posted by josem

So for the 1.6 LW Focus, manual says 95RON preferable but e10 acceptable. Is regular e10 which is around 91RON safe or should I stick to straight unleaded 95 or 98 RON ? The 1.6 sigma engine is similar to ST Fiesta and the fiesta does not require 95RON.

Regular E10 can range anywhere from 91 to 95ron if what I've heard is true.