If your car has a map on it for 98ron then use it, it will workout cheaper and you will get more power.
The M140i definitely needs it.
My 335i was down 30hp on 95ron, rolling roaded it to prove it too.
Used to get 26mpg on 95ron and 29mpg on 98 ron.
Many cars have knock sensors and different maps for different fuels.
All UK cars are designed to be able to take 95ron, but that is a minimum, may will benefit and all their figures are given for 98 ron.
Engine in my car is the Honda 1.8 i-vtec (petrol)
As I have spent many years using diesel cars I was used to filling the tank with BP Ultimate on a long run (found BP to be the best) and a week before M.O.T time to assist with emissions.
This is standard practice in Spain on older cars & most I know do this as the cars pass after failing using standard fuel, we read that the additives in the fuel also increase power a little and help clean injectors etc.
Back to the petrol.
Again on a long run filled with Tesco premium unleaded but found the fuel consumption to be not as good as Asda regular ?
Tried this a number of times now from the Midlands to Kent and back (now based in the UK)
The M140i does not NEED premium fuel it will happily run on 95 as mine has for nearly 2 years now.
There is no separate map for 95 and 98 ron, the cars simply adjust ignition timing if they detect knock which can result in a small loss of power higher up the rev range where 95 fuel becomes more unstable and less resistance to pre ignition.
No of course it doesn't need 98 to run, my point was you are silly not to use it. On 95 as you say it retards the timing (when I say map I mean that it is all done with an ecu these days not manually) and thus you get a reduction in power.
In the case of the N54 and N55 that reduction is massive.
I dropped nearly 30hp using 95 ron, I only found this out as I thought I had an issue with my car, so took it into someone I use for tuning and he rolling roaded it for me. Turns out after lots of head scratching my wife had filled up with 95.
After a couple of tanks of 98 it felt back to being lively again, it had its bite back, we put it back on the rolling road and sure enough the power was back.
Just to double check we put 95 back in.
I do the same run from Wymondham to London all the time, so can go through a tank of fuel every 2 days, and this allows me to test MPG between cars and fuels quite easily and it is very consistent.
95 ron used to be 26mpg no matter what, if you left the OBC it would always end up back at 26mpg in the end, however on 98 ron it would always end up at just over 29mpg.
The fuel usually cost around 5% more to go super unleaded and I saw a constant 10% improvement in mpg and a massive difference in response on the car.
As I said, bit silly not to use 98 in these cars.
In a world where people have always spent £10' of thousands on petrol cars to see a 30hp increase, being able to get those gains by using the right fuel is a surely a no brainer. When you consider you don't even spend more in real terms because of the mpg gains it is even more of a no brainer.
https://www.avforums.com/attachments/4329397677_8dcd13c754_o-jpg.1079787/
Is your car set up for 98ron?
One thing to note, adding 3/4 of a tank will do nothing, you need to make sure it is all 98 ron in there, so normally the benefits are after the second or third tank.
However, add 1/4 a tank of 95ron and it will drop back immediately.
Do you know what Sainsbury add to their petrol?
Everytime I put in Sainsbury petrol, Thetford station on A11, as soon as I have done a few miles the EML comes on.
When scanned it says "N0x sensor fault" and "Contaminated or unknown fuel additive detected".
It took me months to realise it was the fuel, even Mercedes said it was faulty n0x sensors that needed replacing.
I also used 95 on the E350 (M276 engine) for the first 30,000 miles I had it, as all UK literature said 95. However, I then downloaded a brouchure and it was German, in that brochure it was showing Benzine Super Plus for my car.
Started using 98 and you could easily feel the difference and again, MPG increase. 27 average over 30k miles to just over 30mpg for the next 25 since then.
Loads of posts on the Merc forums about Mercedes telling people they need new n0x sensors, however, I think they are just too sensitive and don't like certain additives.
If I was on track id put premium in, sat in traffic reaching a top speed of 40mph I can live with losing 25.5 bhp from an engine capable of 340-350bhp
That's fair enough. Your choice.
You must tack your car lot then?
Long ago I decided for when I am sat in traffic at 40mph, which is alot, I no longer wanted 911's, M3s or 130i's, I moved to big Mercs and BMWs with 17" wheels and just went with the comfort factor. Bought an older M3 for weekend blats.
But then I am now mid 40s so getting old and miserable, and I swapped the M3 for an old wafty ML that is even more comfy and slow as fudge. Haha
98 is cheaper overall on these plus it has better cleaning benefits too.
Tesco 99 is great in these, and often as cheap as Shell regular, worth giving it a go over a couple of tanks.
I wouldn't track the M140i on standard suspension, its more GT then race car. Use to track my Elise though and put V power in that.