While MGF fuel selection might seem like a simple answer, much like with MGB engine oil choices, it can trigger debate and a lot of opinions. When consulting an MGF owners manual (RCL 0332-EMG 3rd Edition) the statement is quite clear. Fuel should be 95 RON Unleaded to EN228. Relatively easy if in Europe, not so simple in the USA.
USA Fuel Selection – Premium 91 (R+M)/2 or Better #
For this knowledge base item I am just jumping straight to the answer. In the USA you should be using premium fuel. This is minimally 91 or better using the (R+M)/2 standard also known as Anti Knock Index (AKI).
Why? Because the conversion from the RON fuel octane rating standard to the USA (R+M)/2 standard says that the closest equivalent to 95 RON is 91 (R+M)/2 (the octane standard used in the USA).
Background Information #
So, there’s probably little point trying to re-explain RON vs MON vs (R+M)/2 also known as AKI. There’s plenty of explanations already out there. Perhaps this one on Wikipedia is a good starting point and you can search more if you wish. In Europe the RON number/value is used. In the USA, the pumps display the (R+M)/2 value. This uses the average of the RON and MON values.
Additional Details #
In the UK 95 RON is the lowest grade petrol you can generally buy. It is also now called E10, because it has 10% ethanol. Whereas “regular 87” is the default in USA. The problem then is that the regular 87 in the USA is only about 91 RON. Which is quite a bit below the 95 RON specified. Now, I am sure some people are running their MGFs on USA 87 or mid-grade 89. Potentially they are not having an issue. The later MGFs and the more modern MEMS3 engine management system may be able to adjust the engine if lower octane fuel is detected.
| RON (Europe) | MON | (R+M)/2 USA |
|---|---|---|
| 90 | 83 | 86.5 |
| 92 | 85 | 88.5 |
| 95 | 87 | 91 |
| 96 | 88 | 92 |
| 98 | 90 | 94 |
| 100 | 91.5 | 95.75 |
| 105 | 95 | 100 |
| 110 | 99 | 104.5 |
I see posts in the UK about using certain brands of petrol and higher RON ratings. For example Shell V Power and 98 RON (which would be USA 94 on (R+M)/2 scales. Does it make a difference? I don’t know and I frankly doubt if you could tell any difference from sitting behind the wheel. But if you are paying for premium petrol in the USA and getting 93 vs 91 (R+M)/2 then so much the better I guess. More/higher octane doesn’t seem like that would be a problem, although everything within reason.
Other Materials #
I’ve built this website and spent time on the knowledge base to bring together a lot of information I have collected from around the internet. The intent is making it easy to find rather than having to know about and have skills with search engine query terms to get what you were looking for. Please make use of the knowledge base.
