Optimax Fuel

Post by **CitroJim** » 09 Jun 2005, 00:11

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by citroenzx

so is the better MPG because of the fuel or because you dont have to drop the pedal a far?
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Part of it comes from running the timing where the engine designer decided it should be and the other from the fact that the higher octane fuel burns better.
You'll only see a difference on engines designed originally to run on 97 RON and have had their timing reset (retarded) to run on 95 RON.
A motor designed to run on 95 RON will show no change running on 98 RON unless you can advance the ignition timing to take advantage of the higher octane fuel. If you can, advance until detonation just sets in under load and then back off a tad.
The reasons behind all of this are a really interesting subject and I could add many lines to this submission going into it. If anyone is interested I will.

PowerLee · Post by **PowerLee** » 09 Jun 2005, 00:27

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Forth

Getting a new (2-stroke) brushcutter on Friday... anyone know if the ultra type of petrol is better to use in them than the ordinary grade?
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Dont forget to use 2 stroke oil aswell!
Also if it comes with a Champion spark plug fitted, Remove it & stick a NGK / Bosch one in there, Champion plugs & 2 stroke engines are not a happy mix.

Homer · Post by **Homer** » 09 Jun 2005, 01:19

Lots of people on Pistonheads forum have done a scientific comparison and recon the savings outweigh the extra cost.

Stempy · Post by **Stempy** » 09 Jun 2005, 04:40

It's more down to the engine management system that the fuel. Most modern petrol engined cars have a knock sensor which tells the ecu the instant detonation starts, then the ecu sets the ignition timing just before that point. If you fill with a higher octane fuel then the ecu can set more advance and hence improve performance. If Optimax is more resistant to knock than other unleaded then this would account for the improved performance. If your car does not have a system which can vary the timing depending on fuel octane then you will get no performance benefit from using a super fuel unless you move the timing manually.