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MG MGF Technical - Octane rating

Does any one have experience of Shell Optimax? Shell say that you should notice an increase in performance, because of its RON of 98, especially when accelerating!

Q1 Can anyone confirm/deny this in the MGF ?
Q2 Can a higher Octane rating damage the engine?

The following is an extract from Shells web site.

"What is octane rating and how does it affect the running of a car?

The octane rating is a measure of a fuel's resistance to knocking. Knock, also known as 'pinking', occurs during combustion when the fuel-air mixture explodes ahead of the flame front rather than burning smoothly, causing a knocking noise. Using a method established in 1929, petrol is rated on a scale of 0 - 100, and given a research octane number (RON). In the 1920's petrol has an octane rating of around 50 to 60. Today, Lead Replacement Petrol has a minimum octane of 97 RON, Unleaded of 95 RON, Super of 97 RON and in August 2001 Shell introduced Shell Optimax, which with an octane rating of 98 is the uk's highest octane petrol."

Beware the US/Canada uses a different Octane rating system at the gas pumps than most other countries. The RON above is UK based.
Stephen Ratledge

comments here and elsewhere seem to be "suck it and see" with some people reporting each of the three options on economy, and both of the options on acceleration.
The talk indicates that the engine needs to be tuned to take full advantage of the richer fuel (which will make it unable to take normal unleaded)
So my opinion is save your money, and buy a K&N then sports exaust, then try it.

Will Munns


The MGF I received in Australia has a metal tag across the inside of the fuel cap which says that you have to run the car on premium unleaded.

The premium unleaded types we get out here are Optimax and BP Ultima. Both are RON 98. There doesn't seem to be any problems at all running the car on either.

As for the performance, I couldn't comment as I won't be putting the standard unleaded in it.

David Crawford

We run both our MGF and ZS180 on optimax now as we definately get better mpg on it. usually 4 mpg better. As for performance gains it is not at all noticeable but both cars seem very smooth on it.
Nik & Anita

Q1, I have found some interesting benefits in fuel consumption on some of the occasions I have been able to fill with Optimax. These have not been consistant and that is why they remain just 'interesting'! Mind you I haven't seen any worse returns.

Q2, No it won't.

However some MEMS systems could have a dealer (Testbook) induced alteration to the ignition mapping to counter complaints of poor performance. This provided some advance of the timing and as a result would be accompanied by the warning that only 98RON octane fuels should be used from then. I know this applied to MEMS systems with the T16 Turbo engines, but I have no knowledge if this applies to the MEMS 1.9, 2J, or even 3 as seen on MGFs. It is also interesting to note that many dealers were not aware of the T16 application either.

Roger Parker

This thread was discussed between 25/01/2002 and 26/01/2002

MG MGF Technical index

This thread is from the archive. The Live MG MGF Technical BBS is active now.