Octane Issue

[David Galley]

Hey Guys.
I've got a Shiny Narooma Blue Series 3 AU, she's pretty awesome! I've just got a question im hoping to get your opinions on.
She goes good, has been fully serviced (not just a car yard service but a genuine service, oil, filter, leads, plugs ect) but for some reason she runs better on the cheap 91octane gas than on the flasher 98octane.
I've tried to come up with a reason why, but am struggling to. It doesn't run bad on the good stuff, its just for some reason it runs better, starts better and has more power on the dirt gas.
This wouldn't bother me too much except that surely that means im not getting the best out of her.
Would resetting the ECU help this?

Any Opinions on this would be a great help!

[Mr Hardware]

Yes try resetting the ECU if you like
but just remember AU's were built to run happily for their whole life on 91
98 is a waste on an AU anyway, 95 is always sufficient unless you have it specifically tuned for it

[The Monty]

My old AU ran better and got way better economy on 95 with 10% ethanol compared to 98. No idea why, it just loved the stuff.

[Mr Hardware]

Yeah my white AU loved freedom 95 E10 - I used to return 500+k tanks with that stuff.

[robbyj]

I can return 700kms a tank with 91. Dont notice any difference with the "better stuff"
As Mr Hardware said, they were made for 91..

[T3man]

98 has a substantially slower burn rate than 91 - unless you can advance your timing or increase your compression ratio you will be just pushing unburnt fuel down the exhaust. This gives rise to high O2 levels so your O2 sensors tell the ECU to trim back the injector cycle. So you get less fuel in so less power out.

If you want more power and want to use 98 then you really need to look at going either the boost route or go dual fuel with an LPG cam and ignition map (flash tune). The 98 fuel will be close to the same burn characteristics as LPG - performance when on either will be better than the standard 6.

[urbancowboy]

This brings up something i've been talking about with work mates,

Who makes the best premium fuel?

I run shell in my AU2 XR8 which is flash tuned,
one of my work mates runs Caltex in his BA XR8,
and another work mate who rallies swears by the mobil in his two dedicated rally cars!

Perhaps a opinion poll is in order.

[james22]

Originally Posted by Mr Hardware

Yes try resetting the ECU if you like
but just remember AU's were built to run happily for their whole life on 91
98 is a waste on an AU anyway, 95 is always sufficient unless you have it specifically tuned for it

For the 6cylinder models yes...

But the AU2/AU3 XR8 has a minimum required octane of 95...

Put 91 in a 8, and it sounds like you got a monkey bashing the crap outta your motor lol

But on the flip side, the bum-o-meter can't tell the difference between 95 & 98, except slightly better fuel consumption, and a slightly crisper idle in my case

[Day-mow]

that sounds pretty strange. when i 1st got my VCT i could get 350 K to a full tank. from day one i fed it 98 oct and now i get about 470 ish to a tank depending how i drive.

i would think somethings not quite right.

Originally Posted by urbancowboy

This brings up something i've been talking about with work mates,

Who makes the best premium fuel?

I run shell in my AU2 XR8 which is flash tuned,
one of my work mates runs Caltex in his BA XR8,
and another work mate who rallies swears by the mobil in his two dedicated rally cars!

Perhaps a opinion poll is in order.

Ultimate seems to be the hardest pushed of the bees knees in premium fuel. i usually use mobil. the V-power formula is claimed to have been created with Ferrari.

so that doesn't really help.