Discussion
My manual says my car is designed to run on 98RON octane fuel. In the UK Unleaded is normally 95 RON and Super Unleaded is normally 97 RON. Optimax being 98.4 RON (or is it 98.6) is the only fuel normally available in the UK that meets the recommended rating.
DAZ
(13k miles with only 2 lots of 97 RON fuel ever used)
DAZ
(13k miles with only 2 lots of 97 RON fuel ever used)
I contacted all teh petrol distributers/re-sellers to see which petrol was the "best" because it's not quite as simple as a RON rating. Long story but MON has a bearing on the quality of the fuel, RON is for the combustability of the fuel in a predefined situation.
RON+MON/2 = the octane rating overall. Optimax comes out out 92.6 all of the others according to BP Esso etc all come out at 91.6 or less.
Kevin.
RON+MON/2 = the octane rating overall. Optimax comes out out 92.6 all of the others according to BP Esso etc all come out at 91.6 or less.
Kevin.
It's all to do with what the ecu is programmed for. Jap cars for instance are set for 100ron fuel. 'Regular' unleaded in Japan is 100ron, their 'super' is 102ron. Try and bring a Jap car over and run it on 95ron and it won't take long to blow it up. Most Jap imports are re-mapped or run on optimax.
There is a tolerance within what the ecu will let the car run on, a couple of ron at most. I run my Imported Impreza on Optimax only (98.6ron). The ecu would not be able to retard the ignition enough to cope with 95ron.
The higher the ron, the greater the explosion, the faster you go; albeit not very noticeable. Rally cars run on 107ron
Higher ron is also more efficient, so you'll get more mpg.
In the US for instance, although cheap, their fuel is utter crap! It varies, but it's not unusual to find 86ron. I think super is 90-92!
A BMW M3 over here is 343bhp, in the US it's 333bhp. The only difference is the ecu in how it is programmed to take their crappy fuel.
By the way, I don't work for Shell! But Optimax is the best fuel you can get over here by far.
There is a tolerance within what the ecu will let the car run on, a couple of ron at most. I run my Imported Impreza on Optimax only (98.6ron). The ecu would not be able to retard the ignition enough to cope with 95ron.
The higher the ron, the greater the explosion, the faster you go; albeit not very noticeable. Rally cars run on 107ron
Higher ron is also more efficient, so you'll get more mpg.
In the US for instance, although cheap, their fuel is utter crap! It varies, but it's not unusual to find 86ron. I think super is 90-92!
A BMW M3 over here is 343bhp, in the US it's 333bhp. The only difference is the ecu in how it is programmed to take their crappy fuel.
By the way, I don't work for Shell! But Optimax is the best fuel you can get over here by far.
It's not just a question of RON, MON plays a part, probably more important part after all it defines the quality of the fuel, not just the combustability of it in a given circumstance..
Without wishing to appear pedantic research into this will show I'm on the ball, Optimax is the one to use for all round RON/MON ratings.
Kevin.
Without wishing to appear pedantic research into this will show I'm on the ball, Optimax is the one to use for all round RON/MON ratings.
Kevin.
I've tried to run some sort of fuel efficiency comparison over the last month.
regular (which is bizarely called premium here) gives about 29mpg, optimax about 27. This could of course be different driving style, but it was over a month period.
My guess is that for lower RON, the ignition timing is advanced so that the spark happens early before TDC, to stop pinking. (though could be wrong)
If this is true, then surely the bang is fighting against the piston more than with the spark closer to TDC.
Does this have any effect on mileage? (or is it cobblers?)
A couple of months ago, Autocar did make promise on the website to run a back to back objective feature of different fuels. Still waiting though.
regular (which is bizarely called premium here) gives about 29mpg, optimax about 27. This could of course be different driving style, but it was over a month period.
My guess is that for lower RON, the ignition timing is advanced so that the spark happens early before TDC, to stop pinking. (though could be wrong)
If this is true, then surely the bang is fighting against the piston more than with the spark closer to TDC.
Does this have any effect on mileage? (or is it cobblers?)
A couple of months ago, Autocar did make promise on the website to run a back to back objective feature of different fuels. Still waiting though.
sprior said:
My guess is that for lower RON, the ignition timing is advanced so that the spark happens early before TDC, to stop pinking. (though could be wrong)
I think thats backwards, usually higher octane rating allows you to run more advance without getting pinking, as I general rule the more advance you run the more power you develop up to the point where the engine starts pinking and destroys itself.
some more info here www.elektro.com/~audi/audi/toluene.html
plus a way to boost octane.
Tony
Yep, I'm in the position of being 'couldn't be more wrong if I tried'.
What confused me was that I always assumed knocking, (or pinging/pinking/pre-ignition) was the mixture igniting early (like diesel?) due to high compression, so sparking early would stop it. But clearly, sparking later prevents it for lower combustability fuel.
Can someone explain what pre-ignition is, and why it makes a knocking noise please?
What confused me was that I always assumed knocking, (or pinging/pinking/pre-ignition) was the mixture igniting early (like diesel?) due to high compression, so sparking early would stop it. But clearly, sparking later prevents it for lower combustability fuel.
Can someone explain what pre-ignition is, and why it makes a knocking noise please?
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