Which Fuel?

[Jaime S.]

You shouldn't use Premium in a car that's recommended for Regular... ever.

It could cause knocking... and that'll be bloody expensive... especially if you can't hear the knocking.

Cheers,
Jaime S.

 

[MaNiac_VP]

Whoa slow down there Jamie.
Increasing the octane won't cause pinging, or pre detenation, it will cause the opposite. The petrol won't burn completely and will therefore seep down (when cruising, running lean) and washing away films of oil in your head and pistons.

From experience with Holden Ecotecs/EV6 and Fowl-cans 4Ls and Camrys:

Optimax/98RON in a EV6 or ECOTEC is nearly a complete waste of money basically and the people that are reporting huge difference in milage off a tank are basically being misled (or injectors & fuel line are really filty) as your computer recognises it as normal petrol and not a higher octane type that takes more compresion to burn completely. YOUR Holden engine has such a LOW compression ratio it would run on 88RON petrol without pinging! Don't laugh, petrol from remote stations can reach that low as it sits in a storage tank for some time and begins to lose a bit of its concentration.

Your ECU doesn't know how to componsate for a higher octane petrol, therefore will not adjust the timing to suit the different burning patern.

Working as an automotive spark for a Taxi joint, I know for a fact that Optimax and other higher octane fuels will not increase mileage, if anything it will make operating costs higher. We have tested all types of petrol from different places and different times, and this is upto 30 different model taxis.

The only engines we work on that may benefit from this are Camrys & Avalons.
And probably newer engines (GenIII) and any other engine that is damaged or running a higher compression ratio.

 

[death-from-above]

Geez well there you go

I think thats gonna put the cat amongst the pigeons!!

 

[MaNiac_VP]

My aplogies if it comes over as a bit harsh.

I have just had this conversation many times with taxi drivers expecting more Ks from a tank and rarely seeing any diffrence.

Don't get me wrong, the cleaning properties are good in these petrols and I run them trhough my VP every now and then.

if you notice your car isn't running 100% unless its running on Optimax then I would seriously consider flushing and cleaning your petrol lines, putting a new filter and/or swapping your injectors with Aznew injectors.

 

[jafo]

ok im adelaide and my local shell dont have a fuel called optimax is that just a name for premium unleaded or do i have to keep searching for it.

havent looked at bp yet as we dont seem to have a lot of them here
but if i find one whats the equivalent to optimax.

i know this sounds stupid but if you dont know how ya gonna learn.

 

[Robbie]

Hi Jafo,

I found that a lot of smaller shell's still only stock Premium Unleaded but all the bigger ones have optimax. I don't know the real reson for some having and some not but it is a step up from their Premium Unleaded.. I think...

Cheers,

Robbie

 

[jules]

maniac,

that's good advice. octane is misunderstood by a lot of people, it has a specific purpose and doesn't always help you go faster. the only thing i'd add is that optimax may give you slightly better fuel consumption, because it's supposed to have more energy density. that has nothing to do with the octane rating and won't cover the extra cost anyway.

 

[MuNtEd]

i use bp pulp

i have notice a great diffience in performance and eco
would'nt go anywhere else...

 

[portercg]

Wow! fuel topic..

Ecotecs (& most engines built after 1990) have a thing called a knock sensor. This gadget and and combined inputs from the other sensors give your ECU the ability to change the fuel & timing settings within milliseconds of getting the data. (that's ess than the time the crank takes to do a full turn at speed)
Mechanically, the lowish compression ratio of an Ecotec for instance says the engine will perform and make good power on 91 unleaded fuel.

But the variable is the operating environment, if is different, eg fuel quality & air density, the ECM will recognise this and adjust the settings so power/torque given by the engine will depend to some degree on what's happening around it, (could be a dyno room, could be night time on a mountain top, could be the desert in summer..) and the condition of the engine itself (eg age of the car, the manufacuring tolerances these engines are built under, is it modified from standard, condition of the injectors, spark plugs etc. are there vacum leaks present, are the electrical connections good, it goes on.)

So everyone's right given their own experiences with their particular cars because nobody knows how their cars behave day to day than the owner.

but be warned. Even though your engine can alter it's tune setings "on the fly" you still MUST have your scheduled maintenance. Good fuel can sometimes mask other problems. especially the injectors, have them removed & cleaned & checked by a pro if your car has high km. But thanks for the tip on Optimax & BP. I've been using Mobil myself. sorry this is a bit wordy but I hope I have been able to give a diplomatic view.

 

[MaNiac_VP]

I agree about the age of the machine, the condition of spark plugs, injectors etc, but in a standard EV6 ECU or ECOTEC there is no method in the ECU to reconginise a higher octane petrol
There is one which says:

if knock sensor detects a knock, then do not advance timing.
check for knock, if no knock, keep timing.
otherwise lower timing.

Nothing at all about reading a higher value and advancing the timing to suit the longer burn.

Thats why when you get your car chipped, they say use 98RON, because the after market chip is made to increase timing for the higher octane petrol.