More trivia to waffle on about when I'm 3 sheets to the wind . Been trialling 95 in the car verses 91.

Octane rating or octane number is a standard measure of the performance of an engine 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 gasoline 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 fuel into the air which was heated by compression. Gasoline engines rely on ignition of air and fuel compressed together as a mixture, which is ignited at the end of the compression stroke using spark plugs. Therefore, high compressibility of the fuel matters mainly for gasoline engines. Use of gasoline with lower octane numbers may lead to the problem of engine knocking.

I used to travel a lot to Canberra, so it was a good opportunity to trial different fuels to see if the mileage/economy was any different. After a reasonable number of trips I was able to confirm that the 95 made no difference whatsoever compared to the 91 (except higher cost!). If you're engines not 'knocking', then there's no point to paying extra.

The 10% ethanol wasn't around at the time. Presumably the mileage would have been lower due to lower calorific value of the fuel, but it would have been good to see what the actual results were in practice.

I've also heard that different Branded service stations have different makes ups in their "so called" "Premium (95) fuels and that you should stick with companies like PB or Caltex. I suppose some where on the internet there is a comparison sheet that unravels the mysteries of the various names fuels.

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Harrow said..
I used to travel a lot to Canberra, so it was a good opportunity to trial different fuels to see if the mileage/economy was any different. After a reasonable number of trips I was able to confirm that the 95 made no difference whatsoever compared to the 91 (except higher cost!). If you're engines not 'knocking', then there's no point to paying extra.

I had the impression that modern engines which detect knock can advance the ignition for high octane fuel and give better mileage .

http://www.ti.com/lit/an/spra039/spra039.pdf

"An engine-knock detection algorithm must be able to adapt to a number of variables to enable the controller to generate optimum spark timing so that the engine can run at the knock threshold."

Ignition timing will be set to whatever fuel the car is rated for. ie; a car tuned for 91 will not advance the timing if you put 98 in it, however if you get a bad batch fuel (old or contaminated) it will pull timing if it detects knock.

Air temp can also lower knock threshold so it can be wise to run higher octane in hot weather.
I used have a vs commodore that would knock in hot weather on 91 but not 98.

Most cars/bikes will pull timing automatically as the air warms up. My Yamaha Fz1n will easily loft the front wheel in the first three gears under 25c (intake temp display on the dash) but over that the computer pulls timing and it struggles to come up in first. Lovin the cool days!

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Crusoe said...
I've also heard that different Branded service stations have different makes ups in their "so called" "Premium (95) fuels and that you should stick with companies like PB or Caltex. I suppose some where on the internet there is a comparison sheet that unravels the mysteries of the various names fuels.

I always found BP more reliable (running 98 on modified cars with replacement or piggy back ecus) and going back 3 or 4 years my tuner told me he saw differences on the dyno when comparing the brands. There would have to be a reason why BP is continually significantly more expensive?

That said i get 50-75km's per tank filling up my diesel Triton at PUMA than the Caltex next to it and you'd think PUMA would be a lower quality fuel!

Where I work, as part of my job I [try to] look after around 25 vehicles for my employers.
The fleet is a mix of i20, i30, ASX, yaris, mazda, cruze, polo, porte, corolla - and a few others.

Many of the vehicles do seriously rediculously low km's.
For example, we have a 3 1/2 year old i20 @ 1600 kilometres,
A lot of the above cars average less than 1500 km's per year.

When we sell time expired cars [normally 3 to 4 years old] potential buyers often turn away thinking the odometers are tampered with [wound back]
The reality is these cars are honestly used by little old ladies [retired Nuns] to drive to church!

My biggest problems are batteries carking it, flat spotted tyres from being parked months at a time, and fuel going off!

A lot of the cars running 91 octane run like pigs and smoke heaps when started up.
I ended up reading them the riot act and making them run BP 98 octane.
Since then, all is good.

Apart from dead batteries and square tyres....................

stephen

Plant boot. Does it rattle? Use higher octane fuel.

You'll not get any more power unless you increase the compression. If you do that, you probably won't be running pump gas any more...

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Crusoe said..

Does your car have a modern (closed loop) EFI system ?

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stoff said..
Most cars/bikes will pull timing automatically as the air warms up. My Yamaha Fz1n will easily loft the front wheel in the first three gears under 25c (intake temp display on the dash) but over that the computer pulls timing and it struggles to come up in first. Lovin the cool days!

That's probably air/fuel mixture discrepancies (and not octane) due to your bike's fuelling system being out of cal when cold. Your bike's EFI most likely has a closed loop (emissions) map and the open loop (power) map and the cold condition is probably causing it to use the open loop map in lower revs (cruising rev range) and hence will have more power.... I could be wrong though. I used to have a GSX-R1000 that had a similar condition. First fuel injected Gixxer model.

I do the run between Perth and Geraldton often enough, sticking to the speed limit (actually about 4 over) I can say without doubt I get better mileage out of 95 RON over what I get out of 91, but there is little difference between running 91 and 98. Go figure.

If you want to keep the fuel economy down it's about how you drive, I can get my car down to 5.6 L/100 over the 400km journey where the manufacturer claims 7.1. Time it with a tail wind and the cool of night I might get 5.3. A decent headwind can easily add about 20%.

Just marketing gimmick, there are more BTU's in low octane fuel than in higher octane. Nearly every newer car is designed to run on regular so unless you have a Ferrari or something it is a waste of money.
Also all brands of fuel come from the same refineries, the only difference is the different additives.

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MDSXR6T said..

Crusoe said...
I've also heard that different Branded service stations have different makes ups in their "so called" "Premium (95) fuels and that you should stick with companies like PB or Caltex. I suppose some where on the internet there is a comparison sheet that unravels the mysteries of the various names fuels.

I always found BP more reliable (running 98 on modified cars with replacement or piggy back ecus) and going back 3 or 4 years my tuner told me he saw differences on the dyno when comparing the brands. There would have to be a reason why BP is continually significantly more expensive?

That said i get 50-75km's per tank filling up my diesel Triton at PUMA than the Caltex next to it and you'd think PUMA would be a lower quality fuel!

Having worked at a Caltex refinery I can tell you there was a great big pipe across to the BP refinery across the river, with a tee off to the Shell tank farm.
Flows of different products in different directions depending on need.

There's absolutely no reason to favour one brand over another.

BP is consistently more expensive due to that being their strategy, to be 'premium' and rely on people making the assumption that there's a reason for it.
In a very competitive market it's a way to beat the pack.

I can also add that all fuel is made to a specification and blended to be on spec - so it' s more or less the same... but each 'batch' is very different, because it's a blend of components and they can be made from different batches of crude which have very different chemical compositions and then the final product is brought to spec usiing different blend stocks.

The biggest noticable difference you'll get in fuel is when there's a problem at a servo (contaminants), or when it's a quiet servo. Busy is good.

Beaglus is not really right IMHO. The leaner an engine runs the more k's it will go on a litre of fuel. Modern cars self-tune to the leanest possible without pinging, and therefore will travel more k's on higher octane fuel (because you're burning more air and less fuel), but not quite further enough to cover the cost difference. But leaner = more power because more oxygen = more burn, so you get more power and more detergenty additives with premium fuels.

So you end up paying a little extra per km, for more power and slightly better engine internal reliability. For me, with sports cars, it's worth it.