Thread: Hi Octane fuel

Octane is the ability to resist detonation, allowing higher compression or more adavanced timing. (both = more power).

Energy density is what they dont tell you, but claim anyhow. The higher, the (potentially) less you need to add to get the same HP.


Ethanol has a higher octane and a lower energy density to ULP. So it wil lbe less HP/mileage per litre unless you have an engine that can take advantage. (as mentioed before, either high compression, or good advance systems).

Premium, often badged '98', is /typically/ denser, and has the high octane.

Cheers!

Just to throw another spanner.
Ethanol has only 60% of the calorific value of petrol, so 10% ethanol should yield 4% poorer fuel economy than straight petrol.
So the price difference of 4 cents is really nil.

BUT just to add to the subjective nature of the argument, I cannot say I have noticed any reduction in fuel economy using E10, which I have tried a couple of times.

AND re the LR 6 cylinder. They have such a low CR that I doubt they would ping until VERY advanced, and if you didn't hear it, severe damage could be done to what is now a totally obsolete engine. So I wouldn't advance it too much.
Regards Philip A

Originally Posted by Panda

Thanks Phil,

I have no idea what "closed loop feedback" is or "knock sensors", but I'm guessing none of this would apply to my basic 6 cylinder Landy?

Thought it was too much of a coincidence, maybe it was just wishful thinking. I've also noticed it seems to run better in colder weather? Any substance to that do you think?

Thanks for your input, much appreciated.

Running better in cold weather is due to denser air, meaning more oxygen to support combustion. Meaning the burn is more thourough, or potentially more fuel is added also (EFI).

The better HP from premium on an engine with no dynamic advance control, no dynamic mixture control, etc is a tough one. Energy density would be my suggestion, but im not sure how that effects the stochiometric ratio. Burn speed is the other potential, but i dont know if premium burns faster or slower than standard petrol.

So yeah , there is probably some substance. A friend with a BMW 130i did a fairly thourough test between 91 and 98 octane from one fuel supplier. With 11.1 CR, and quality engine management, he was getting significant fuel savings. Which means more power per fuel.

Cheers!

Originally Posted by beforethevision

Running better in cold weather is due to denser air, meaning more oxygen to support combustion. Meaning the burn is more thourough, or potentially more fuel is added also (EFI).

The better HP from premium on an engine with no dynamic advance control, no dynamic mixture control, etc is a tough one. Energy density would be my suggestion, but im not sure how that effects the stochiometric ratio. Burn speed is the other potential, but i dont know if premium burns faster or slower than standard petrol.

So yeah , there is probably some substance. A friend with a BMW 130i did a fairly thourough test between 91 and 98 octane from one fuel supplier. With 11.1 CR, and quality engine management, he was getting significant fuel savings. Which means more power per fuel.

Cheers!

The joys of the better management systems, all they do, is advance till knock, then back it off, constantly, to maintain, good burn and economy, impressive to see it on an interface

After hearing quite a bit of anecdotal evidence from friends and on talkback radio about how people were getting "50 kms further on a tank" and such things when they used premium unleaded, in spite of my natural scepticism, I decide to give it a trial.

I tried three tankfuls in my 1988 Camry and found (surprise, surprise) that it made absolutely no difference whatsoever. Power seemed the same and fuel consumption was definitely exactly the same as always.

It confirmed what an NRMA engineer had said on the radio. If the engine doesn't need the higher octane, it won't benefit from it.

More sophisticated, modern engines might give different results, but in mine it made the same difference as fitting a Hiclone.

The vox populi seem to believe that the RON refers to the fuel's calorific value, this misinformation is a bliss to the fuel companies when Mr. DH fills his 1978 Kingswood with 98 thinking that he is making massive savings because the car "goes further".

Originally Posted by Panda

Hi Mick,

I had a look at the manual which reckons the timing should be 2 ATDC with 90 octane, 6 ATDC 85 & 2 BTDC with 83. All very confusing. What's the difference with ethanol? I thought ethanol was the same as premium (yes, I know, showing my ignorance but hence I seek all your expert advice!)

So what should the timing be set at for premium? Are different premium petrols (e.g. Caltex, Shell etc) all the same octane levels, or are some higher or lower?

What does more "bang for your buck" mean? Does that mean it fires/ignites better?

Thanks

Firing ATDC sounds like a waste as the horse has already bolted so to speak. That the fuel is probably too good for the engine and a waste. If they are the specs you're probably better off running it on the lowest octane fuel (reg ULP) and setting the timing to suit.

Ethanol is just a fraction, or component of the fuel blend. The attraction of Ethanol also is that it is a renewable fuel, much like B10 is for Diesel (Biodiesel).

In NSW at least, there normal seems to be regular ULP at 92 octane, Premium ULP which is 95 octane and Premium 98 ULP which is 98 octane. Some Premium 98's have special names like BP Ultimate or Shell Optimax.

[QUOTE=Slunnie;712271]Firing ATDC sounds like a waste as the horse has already bolted so to speak. That the fuel is probably too good for the engine and a waste. If they are the specs you're probably better off running it on the lowest octane fuel (reg ULP) and setting the timing to suit.
[QUOTE]

Yeah, i agree, ATDC sounds waaay late. I got no idea about older engines, but with a stock yamaha r6 engine in a formula SAE car, we run up to 25deg advance at WOT (on 98 octane).

Cheers!