Fuel Octane ratings

[PeterGee]

Just had my heads on my 2.8 fitted with hardened valve seats so that I can safely run unleaded. Machine shop did great job and also fitted new guides. Not a sound now from the valve gear. Anybody know what the octane rating of Shell Optimax is and does this stuff make any difference to performance. Ignition timing is set at 12 deg BTDC which is standard for the 2.8 and there's no sign of pinking even under full power so just wondering if it was worth switching to this new brew.

[Matty2148]

i looked at the shell web page and it says its a 98 octane
heres the link: http://www.shell.com/home/Framework?sit ... -2003.html

the link should be ok

[BrettmkI]

if the cars standard i shouldnt worry to much about running on optimax, iv only really found it to be of use on a car of a higher state of tune or higher cr/boost where that extra ron is needed. some may think different im not sure but im certain they will remark also.

[R0A0C0H0E0L]

Optimax is designed as said for highly tuned/turbo engines. I've run it in 3 different cars.

1)Corsa 1.2 (company car:
I put optimax in when the car had 4 miles on the clock and ran it for a few days, it seemed rough so i changed to normal unleaded and it was fine after that.

2)Astra GSi (turbo)
This was running on normal unleaded again when i got it, tried optimax a bit later and there seemed to be an increase in performance. It was more responsive and seemed more powerful. It could have been in my head but it did seem better.

3) Peugeot 206 1.6 16v
I got this with 6 miles on, (with a full tank or noirmal unleaded) I ran it untill the fuel got low and filled it with optimax, next day sure enough the engine was quite rough. When it ran out i put normal unleaded back in and it's now running fine again.

I wouldn't bother with optimax, maybe every now and again as it's supposed to be good for cleaning injectors etc but I was not impressed with it.

P.S. - If u can explain why an extra 3ron can cause crap running please tell me because shell couldnt explain it and neither could vauxhall technical UK

[BrettmkI]

could be just the car needed setting up for the different fuel?
I know as ive said before my R5 turbo will only run nicely on the fuel i tuned it for, if i switch between fuels without tuning i start getting some stuttering, i always used to carry a small mixture adjusting screw driver and a gas tester when i went to the strip with optimax and a bottle of avgas, got me ruffly right it'd take 3 or 4 runs to get it runnin sweet tho.