Should I be using super unleaded?
Discussion
rayyan171 said:
What exactly would it do?
It will allow the engine to run as the designers intended rather than it switch to a 'safe'/'retarded' map to ensure the cheap fuel doesn't damage the engine.Even a humble naturally aspirated car (admittedly with relatively high compression ratio) like my Swift Sport runs better and gives better mpg with premium fuel than cheap fuel.
With Tesco Momentum, it will happily pull 6th gear at 30mph but with Tesco regular petrol it'll only pull 5th and even then it's not entirely happy. Also when under load (low-rpm cruising) or hard acceleration it's appallingly thirsty when using cheap fuel.
I'd love to use cheap fuel to save £££ - and even my SSS' filler flap says '95' - but there's a clear difference between 95 and 99.
I've never run a 3.0 TFSI, but if it helps both my current 2.0TSI and previous 2.0TFSI Octavias had better fuel economy on super unleaded by about 10% (sometimes I drive to places where 95 is all that's available), so the premium for super unleaded pays for itself.
It is worth it, but only for vehicles in a high enough state of tune to take advantage. Yours certainly should be, in my opinion.
It is worth it, but only for vehicles in a high enough state of tune to take advantage. Yours certainly should be, in my opinion.
daemon said:
Both our cars run on super unleaded and we'd only put unleaded in if we'd no other choice.
When I'm forced to accept 95, where possible I only add a roughly equal amount of 95 to the remaining 99 in the tank, so after the top-up I'm running on ~97 until I can find some more 99.Most modern cars can readjust for different RON petrols no problem. Further reading however has shown that Audi actually map these cars from factory to run at their claimed horsepower (290hp) on standard 95 RON fuel. Seems like higher RON gives better fuel economy but not different worlds in the power department. Still not sold on it, however I do understand that this is a high performance engine which may run better with it. Have also read of misfires on cars switching to higher RON fuels however!
rayyan171 said:
Most modern cars can readjust for different RON petrols no problem. Further reading however has shown that Audi actually map these cars from factory to run at their claimed horsepower (290hp) on standard 95 RON fuel. Seems like higher RON gives better fuel economy but not different worlds in the power department. Still not sold on it, however I do understand that this is a high performance engine which may run better with it. Have also read of misfires on cars switching to higher RON fuels however!
You ignore Audi recommendations and use an online forum as a reference? 🤦♂️ Don’t believe everything you read.anonymous said:
[redacted]
Indeed.All you need is a performance car for the pub bragging rights.
Doesn't matter if it's running on cheap fuel and ditchfinders because your mates won't find out and most performance car owners only have them as front garden ornaments for polishing on a Sunday afternoon.
rayyan171 said:
Have also read of misfires on cars switching to higher RON fuels however!
We're talking 97-99 RON, not jet fuel. 
And your car is designed for 98, and will cope fine in that range.
Sometimes posters come on here asking for advice, and people try to give it. Sometimes I think that other people come on here hoping that people will validate a decision that they've already subconsciously made. If that isn't you, then I'm sorry- but it is how you're currently coming across to me. If you've already decided to save money- which I don't think you will- by using 95 RON, go ahead. You're a grown man, and you're allowed to disagree without anyone being upset.
It's not like you're running on on coal, and it's still better than most petrol you'll get in the US- just don't a lot of us to agree with the choice you've made. We'll still be polite and nice about it though. 
Edited by blearyeyedboy on Monday 7th May 10:12
Fact is, the car is being driven by someone who does very little miles and mainly doesn't care about the peak power at 7000 RPM. But, there's other drivers that might be interested in the household. Was just wondering whether it would actually be better for the car in the long run, or whether it was worth putting the better fuel in, as if these cars really do run stock figures on standard fuel then there is no point putting better fuel in.
rayyan171 said:
cap says minimum 91 RON otherwise 95 RON
Cap on my humble Swift Sport with 1.6-litre naturally aspirated engine also says 95.But with 99 it will pull a gear higher around town, revs more freely through the range, and gets slightly better mpg.
Premium fuels would be expected to have more of the supposedly-beneficial additives.
Also, the earlier model Swifts with the same basic engine were designed to run on 98.
So I use 99 in my Swift Sport.
However, your everyday 10x compression ratio naturally aspirated engine in typical cars probably won't be able to make use of grades higher than 95.
rayyan171 said:
I contacted MRC regarding tuning options for an Audi S4, one of the comments they made was (and I quote);"As the S4 is a high compression engine it cannot be stated enough that these engines need high octane fuel. We have seen standard engines fail on cars run on 95RON".
Make of that what you will...
I think it will be best to try the car on super unleaded for a while, and see how it goes. I do guess that as it's a high performance engine it should be treated so, the engine oil argument people make here is true. Would it make a difference that this isn't an Audi S car? It's the identical engine to the S4 except it is derated to 290hp from 333hp, with a different engine code to add as well (CAJA for the A6, CAKA for the S4). Would the engine have been derated to allow for more standard fuels? The compression ratio does not change in both engines.
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