Will it be ok to run a car on tesco99 when the car is mapped for optimax?
i have heard conflicting opinions

 

I used to run optimax and now run only tesco 99. Suffice to say my car runs alot better, however as we all know even though 2 cars could be identical there may be differences in results. Give it a try. Although i would say it should not do any harm as it runs very well on my tuned STI8.

Hope this helps!

 

I would have thought that if the car has been specifically mapped using a certain fuel then you should stick to that fuel otherwise you could lose performance etc. Best ask Bob Rawle or Andy Forrest m8.

 

Tesco 99 is 99 octane. Optimax is 98. Logic would suggest that if your car is mapped for 98 octane fuel, it will run fine if not better on 99.

In the same way, cars designed for normal unleaded can sometimes run better, but at the very least just as well, on super.

No doubt there are the Shell fan club who will always defend their overpriced 'premium' petrol, but octane is octane IMHO.

 

the different octane fuels have different ignition characteristics so a higher octane on a car specifically mapped for a certain fuel will not neccesarily make more power on a different octane rated fuel, as the map is specific. However with oem ecus then there is scope for added performance as it is a general map and not an individual one, so it has scope for variencies if you see what I mean. I only know this as I filled with tesco 99 last night, I let my mapper know and he explained that it is possible it could affect performance slightly (maybe more knock as the ignition isnt set for that fuels characteristics)

 

Yes I know what you mean that different fuels have different characteristics, but octane, by its very definition, is resistance to knock. The higher the number (measured on the same scale of course e.g. RON) the less prone the fuel is to detonation. And this is not affected by hearsay and pub talk - it is a repeatable standardised scientific process. A 99 octane fuel will be more resistant to knock than a 98 octane fuel, assuming they are fresh and have not 'gone off'.

What I'm trying to say is that 99 octane fuel simply cannot be more prone to detonation than 98 octane fuel - whatever the engine, whatever the map - and whatever the forecourt it comes from.

If it was mapped on Optimax, run it on Optimax. But I'd be very surprised if running on Tesco 99 would do it any harm at all...IMHO. I personally would run an Optimax car on Tesco 99 without giving it a second thought. I wouldn't run it on BP Ultimate or any other Super Unleaded.

There's obviously doubt in your mind about this issue otherwise you wouldn't ask about it on here - you'd just trust your mapper implicitly.

 

must admit mine was mapped on esso 97 but have now switched to tesco 99 as it is about5 - 6p per litre cheaper, it does sound a bit beefier if thats possible but my knock count is a bit higher (25 now instead of 17 on average).
I know a 99ron will be more resistant to knock, but only if it is mapped to that fuel and its particular burn/ignition characteristics (Assuming were talking about a power fc as I beleive this doesnt offer knock correction) so if your car is mapped for a lower level of ron then using a higher octane will not really be beneficial if you see where I am coming from.

 

Read Evo mag from May 2006. It has a fuel development engineer explain all you need to know about petrols, especially Optimax.

 

What I'm trying to say is that 99 octane fuel simply cannot be more prone to detonation than 98 octane fuel - whatever the engine, whatever the map - and whatever the forecourt it comes from.If it was mapped on Optimax, run it on Optimax. But I'd be very surprised if running on Tesco 99 would do it any harm at all...IMHO. I personally would run an Optimax car on Tesco 99 without giving it a second thought. I wouldn't run it on BP Ultimate or any other Super Unleaded.


That's what i thought. Surely its no difference to putting a bottle of millers in your tank

 

can anyone help me ,i have just brought a impreza wrx 1994,its been imported from japan ,what petrol should i run her on ,i donot think its been tuned up for more power ,but it has a very large backbox on the exhaust

 

My car is mapped for optimax but lately have been using Tesco 99 and see a lower knock count on the power fc.

banny

 

steve run it on super unleaded,optimax,its up to you,to be honest it does not need to be mapped for uk fuel as 100 ron fuel was not available in japan at the time your car was manufactured.I have had several imports with mods and ran them on super unleaded or optimax without re-maps with no problems at all.There are a lot of people who will probally disagree but there is no reason why your car should not ok to run on our fuel

 

as he states in his first post it HAS been mapped for Optimax.

You are best to run it on the fuel it was mapped on. It may well run fine on 99 but ideally it should be checked but if you are cautious you should be okay.
Tend to find the increase in octane is done using different addictives which dictate a different fuel AFR target.. therefore yes it may be a higher ron but should be injecting slightly more fuel or slightly less fuel to keep the AFR correct for the different fuel.
Going from Optimax to 99 Tesco is the safer direction, tend to find 99ron allows around 1degree more timing depending on the car etc.. so going from tesco99 to optimax would be more inclined to be nearer det.

Simon