Nice one Rob. We'll have Denis on the run before you know it!

Originally posted by robmawer in this post

AFAIK Optimax is 98 RON, or maybe 99. Super Unleaded should be the same, as it was originally designed as the higher octance version of unleaded.

Well Rob, Shell themselves don't seem to know either - or don't want to us to know, as they are very cleverly shying away from naming the exact octane number!

Naturally very interested in this Optimax stuff for my trip to the UK in September I followed the link supplied by MonkeyHanger and clicked on the obvious 'All about Shell Optimax', hoping to find out more about the RON. And there, yes, was our question 'What is the Octane level of Shell Optimax?'

The answer reads thus:

'Shell Optimax has the highest octane specification of any petrol in the UK. It is greater than 98 Research Octane Number (RON).'

So, greater than 98!

But lower than 99?

I'm curious - what is the price and performance gap to your usual Super Unleaded 98? And is it worth it?

Well, I've never had a car that justified the extra cost for the increase in

performance!

I do know of some people with Japanese import Scoobs, which are tuned

to run on Japanese fuel (which I think is about 100 RON). So they tend to

use Optimax with a fuel booster additive to get the octane to what is

ideal.

So 99 RON for Optimax sounds about right...

Rob.

Originally posted by Chrille in this post

Atleast inside my Rs's tank lid(?) it says 98/95Ron wich I guess means that 98 is recomended eventhough 95 is ok. You can also see recomended tyre preassure. Am I the only one who has this sticker inside the tank lid?

No, I think it's standard (BTW, your usually excellent mastery of the English language has let you down for once - over here the tank lid is usually called a "filler cap").

The sticker on mine specifies 95RON/91ROZ (does anyone know what the ROZ standard is?), and has a table of tyre pressures for different size tyres and different loads. Shame it's only in Bar - my digital pressure gauge is calibrated in pounds per square inch :(

Well, with the Oettinger chip 98 will be compulsory for me - or so they say. It will run on 95 but the mixture will probably be too lean.

(How do you call the stuttering effect that gives on the engine? Only know the Dutch word!)

Having used bog standard unleaded in mine for the last 6 months , I have decided to give Optimax a go , only filled up for the first time on Tuesday and I realise that I have to use it a few times before noticing any difference , but hope it's worth the extra cost . Will keep you informed

How do you call the stuttering effect that gives on the engine? Only know the Dutch word!

Could it be: missing (misfiring) or pinking (detonation which sounds like a metallic tapping noise)?