Will my M Roadster run on 95 unleaded?
Discussion
IIRC the ECU retards the ignition a little running 95 RON so it will be down on power, but still run OK.
The handbook states you should only ever use 97 RON so I see no reason why not to! The difference in cost is minimal, and if you get more power then why would you not want to use it!?
The handbook states you should only ever use 97 RON so I see no reason why not to! The difference in cost is minimal, and if you get more power then why would you not want to use it!?
I would suggest you'd notice naff all difference between 95 & 97/8. There are other important factors such as ambient temperature etc.. which will affect the performance.
97/98 is recommended for its RON values, but its also down to the 'Driveability Index' - which is :
DI = 1.5 x T10 + 3 x T50 + T90 (T being vapour temperature)
Ironically, the lower the result (down to about 495) the greater the driveability. High resulting fuel (inc Optimax) is best avoided in cold conditions.
However, you are also looking for 'Start - up' performance, which is expressed thus :
FVI = RVP + 0.7 x E-70
Unfortunately, in UK, maximum permitted Vapour pressure (as measured using the Reid method) is lower than that which is optimal for performance. The permitted pressure has reduced by over 20% since 1986, and a further reduction will occur in 2005.
To summarise, RON rating is only part of the story - next time you fill up just ask the attendant to do a quick Flexible Volatility Index test for you.
Having said that, I am a marketing mans wet dream and only use 97/8
97/98 is recommended for its RON values, but its also down to the 'Driveability Index' - which is :
DI = 1.5 x T10 + 3 x T50 + T90 (T being vapour temperature)
Ironically, the lower the result (down to about 495) the greater the driveability. High resulting fuel (inc Optimax) is best avoided in cold conditions.
However, you are also looking for 'Start - up' performance, which is expressed thus :
FVI = RVP + 0.7 x E-70
Unfortunately, in UK, maximum permitted Vapour pressure (as measured using the Reid method) is lower than that which is optimal for performance. The permitted pressure has reduced by over 20% since 1986, and a further reduction will occur in 2005.
To summarise, RON rating is only part of the story - next time you fill up just ask the attendant to do a quick Flexible Volatility Index test for you.
Having said that, I am a marketing mans wet dream and only use 97/8
I have occasionally used 95 in an emergency but try to use Optimax. Can't say I had a problem with 95 but she has a sticker on the dash that states 98 only should be used. She does drive a LOT better with Optimax (not sure whether this is just in my head though). Way I figure, better to pay a couple of quid extra every tank full rather than a couple of hundred quid for her to be fixed.
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