I use 97 because my car isn’t used regularly and higher octane petrol doesn’t “go off” as quick. Apparently…
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Take a look at the attached article from a previous edition of Hard Top Softtop (what a name!).
It’s from a few years back so some of the stats re government % of ethanol may have changed.
Ethanol corrodes metal and rubber. Personally I always use Shell V-Power in my Mk3 because of this. In my day-to-day car I use it in every 4th tank. Read the article and make up your own mind whether it’s worth paying the extra.
Sorry, article to follow - site will not allow me to upload a PDF !
A recent notice (May 2020) on the Shell UK website says that both their unleaded Regular and V Power are likely to contain Ethanol, but no more than 5%
Other way round, Soft Top Hardtop
Thanks IanH, put that way it doesn’t seem a silly name at all!
Bit late to the party, and comments are caveated on having mk3.5 2.0. Personally I’ve no qualms using supermarket petrol; my rationale is they sell it cheaper, they sell more fuel as a result, so their stock gets turned over regularly. Having said that I do use super-unleaded, and for me, it does make a difference in mpg (not huge, maybe 2-3 mpg) and general driving (pick up, acceleration). My father in law (engineer all his life on aircraft and cars) firmly believed that It improved the mechanical longevity (again, I’ve never owned a car long enough to put that to the test!). My father always uses Shell V-power and reckons the extra pays for itself in increased fuel economy.
At the end of the day, it’s personal choice.
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Maybe. Depends on the car. In a Mk.1 MX-5 I can say it definitely doesn’t, because I was nerdy enough to have noted petrol type and mpg on every tankful for years.
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I think you are unlikely to notice a great deal of difference. In theory the ECU may be able to advance the ignition a little which might give a fraction more power at the top end and it is possible that additional additives will allow the engine to clean itself up a little inside. Suggest you wait until you are empty and put in about 25 litres and see if you notice any difference
Hugh Robinson.
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Hi everyone,
Is there any value in starting to use Shell V Power and BP Ultimate in my 2017 1.5 MX-5 RF? I use E10 now.
I will re-read this thread and will research but any advice and comments welcomed!
Ofiaich 
I think ‘Originalparts’ reply covers this point very nicely and his father’s comments make sense.
I have had my 1.5ND from new 14 months ago, and today just reached the 10,000 mile mark. I have only ever used V-Power, unless on the rare occasion I am caught out, but even then I look for the E5 rated products.
From zero to 12-months I recorded 52.7mpg. Since then my latest calculation shows 54.6mpg. I drive more or less as the car intended, with both relaxed and spirited driving. Does Shell V-Power aid those figures? Everything is naturally open for debate, but I am happy with my lot, and will continue in the same vein.
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Thanks Mike,
I re-read Originalparts reply. I will start using Shell V-Power at the next visit,
Ofiaich 
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Why would you stay away from the supermarket petrol?
Read below…
There is no evidence to suggest that supermarket fuel is inferior quality, as they conform to the same British standards as any other fuel sold and are supplied by many of the same large refineries. Premium fuels such as Shell V-Power may offer additional benefits thanks to additives designed to reduce wear, but you should experience no problems from using supermarket fuels.
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I’ve avoided experimenting with fuel every since we put ethanol pinched out of the physics lab in a schoolmate’s NSU Quickly one lunchtime and sent him off, doing wheelies, down the road.
He reappeared, sad-faced, pushing the machine, which never went again.
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Based on the claims here that e5 pretty much pays for itself, I put a tankful of Tesco Momentum in my 2l Miyako.
It definitely feels perkier, so I will be making that a habit.
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Just as an “aside” of limited interst as it concerns our year old Suzuki turbo. Now with 2289 miles on, fed on “Chanel No 5” from day one, we had no option but to use No 10 a few days back and the difference was as unwelcome as it was a surprise as it’s designed to use 10…but whose I do not know as I know some are “better” than others. What I’m getting now…and it’s no big deal…is an on off effect off the turbo and Hybrid chiming in…not a lot but I can sense it between 2k and 4k. Like I say no biggy…it’s as though the ECUs learned to use 5. I’m not concerned…I’ll just brim it with 5 in a few days… Starts and ticks over as normal…so…
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The Swift Sport forum has had a few posts over the years about that very subject and its effects. An adaptive ECU liking RON99 etc
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Ah, Cheers buddy…wondered if I was imagining it…seems not. Seems Chanel No5 is worth circa 10 bhp -ish with the Adaptive ECUs .Allegedly! So, when I put it all together…the thing has about 140-145 bhp on tap on boost and Hybrid. It certain flies…I’ve taken 2 mills out the fronts though…rears are as new, 
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I’ve driven since the early 70s and throughout that time I’ve heard dark mutterings about the quality of different makes of fuel. I used to sport an AGIP sticker on my Seven and was tasked by some humourless oaf why I was supporting an Italian firm which made bad petrol. (Answer- because a black , six legged dog makes for a very sexy logo ). Times without number I’ve been warned off firm X or supermarket Y .
And guess what? I’ve never noticed the tiniest difference. Apart from once when super unleaded repeatedly gave a 3-4mpg improvement on a MK 2 Golf GTi . Of course there may have been differences but too small for me to notice or car about .
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