Hey guys, we all know that premium is meant to give you better fuel economy and what not, but whenever I use it my fuel economy actually seems to get worse. I drive exactly the same on regular unleaded as I do on premium, I don't just put my foot down on one. So what possible reason would their be for such a noticeable slug in economy on a fuel that is MEANT to be so much better for my engine?

there's:

regular unleaded (91 octane)
premium unleaded (95 octane)
high octane premium (98 octane) e.g. optimax, vortex 98, bp ultimate etc.
shell optimax extreme (100 octane) contains ethanol though

just sticking premium (95 octane) in, will not make much of a difference. shouldn't get worse economy though, unless there's something else wrong (possibly airflow meter?). otherwise you may have just got a bad batch of fuel (end of the tank maybe)

what does make a difference is using high octane premium, and advancing your timing. this should net slight performance gains, and should not result in worse economy.

higher octane fuels allow you to run more advanced timing (of the spark), without pinging (pre-detonation).

don't know if this helps at all though

- Stooge007 out

Blakeyboy, I know what you are saying! My parent's FPV GT goes around 50km further on normal unleaded rather than premium...

But my WRX is tuned for 95 ron (Autronic) so I can't go back to 91 otherwise the consequences will be catastrophic. But I noticed no gains going to 98 ron fuel in performance or economy.

I only use Optimax, I get about 10% better economy, and a little more power.
considering it's only 7% (or so) dearer, that's a cost benfit.

As for 'regular' premium... I found BP/Mobil/Caltex/Other to be not-so-good and in some cases less economical than regular unleaded.

The problem (in part) is that petrol stations which are franchised are not legally bound to use that same brand of fuel, i.e. Shell servo may sell imported petrol, unless that pump is labelled with a Trademarked fuel name - like 'Optimax' in which case it must be Optimax.

If it just says 'unleaded' or 'premium unleaded' then you really don't know what you're getting.

My car's a bit like that but with optimax and premium. I get better economy out of premium then optimax. I've tried ethanol, it was an absolute waste of time and money. My guess is that maybe your car has been tuned to run on regular unleaded.

lower octane levels require less fuel to combust, making it more fuel efficient than higher octane fuel you should really use as low as your car is tuned to use.. going better is fairly pointless without getting your timing advanced to say 98RON.

We find that 98 is cheaper than 95/91 as we get much better economy in the Nimbus.

the difference isnt just octane either. there are quite a bit of difference between the additives used in 91 to 95 and then there are even more differences in the additives between 95 and 98.

octane just makes the fuel harder to burn. eg, it can be compressed more without spontaneously combusting (pinging/detonation). it also makes the fuel burn 'slower' so instead of an explosion u get a flame wave (which is wat most pinging/detonation is, not premature ignition unless something has really gone wrong)

i myself use 95 RON because it makes my engine run smoother. then again, wat one engine will find run smoother will make another engine run differently again.

i know many race bikes wont run optimax because of all the detergents in the fuel gum everything up. whereas i know alot of the old triumph race cars swear by optimax.

in my old subaru leone i used premium, so it ran smoother....thats the only reason why...

i find that if i use premium my engine runs alot better then wat it would if i used normal unleaded.

Makes no real difference in economy in the Civic, however the car does run alot smoother and accelleration seems alot snappier - I find though the high premium fuels make the car exhaust smell, friend is going to reflash my ecu so hopefully there's some gains in both economy an power there.

I used to use 98 in my old car (91-ron required), now in my current car (96-ron required) it seems to run much better on standard 95-ron premium than it does on the 98 ultimate/mobil8000

Stooge..Vortex 98, is it diff with the normal Vortex? Here in Brisbane I've been using Vortex for a year and I thought it was 96..May be its called Vortex 98 in syd?

For fuel economy consumption my camry able to go 60km further..but still..with the fuel price keep going up now and then damnnn I'm broke!

Well I've tried different premiums, different octanes many many times. Anything that's available, I've tried it. All of the premiums give me worse fuel economy, by about 50km per tank. So I guess the only reason is that my car isn't tuned to take advantage of the higher octane fuel? In which case I'd have to get my timing advanced. But then if I did that, I'd have to use the premium all the time correct?

Considering its a VX - should be a change in the computer.
on the old model Barina, there was a plug in the engine bay you could switch from 85 to 91 (or something like that) to use the better fuel.

Try asking a performance place if they know of a simple mod for the computer.

VX ECU should be automatically adjusting fuel maps and timing accordingly. it will take a few hundred k's before u see any difference.

ECU probably went 'oh my god. DIFFERENT FUEL!!!!! i better run a bit rich while i figure thins out'

did u try the same premium fuels for a couple of tanks?

that's a point too - maybe you need to 'reset' the ECU.
not sure in the VX, but when you have the battery off in a VR/VS you need to do certain things for the first day or so to get the engine thinking right again.

Stupid adaptive computers.

Well I usually run one premium tank a month, but that's only because every time I use a tank it does sweet you know what for my fuel economy and performance.
I'd actually like to BENEFIT from premium fuel rather than have it make my driving experience worse.