Only car I've ever noticed a difference in is my 1100cc 1991 Pug 106
On 95 octane, foot to the floor it will wind up to terminal velocity down the bypass on the morning commute . . .
Filled up one week at the local station - they'd accidently filled the tanks with "super" but were still selling it at 95 octane prices . . .
Foot to the floor terminal velocity was a good few mph faster each morning that week . . .
My F80 M3 is definitely a bit perkier on 98 ron fuel (the best that is locally available). Mid revs pickup is better as well as full throttle response.
But it's no slouch on 95 ron either. :)
Don't let it go to your head Derek!
My modern Golf seems to get a few more MPG on 98/99 vs 95. Cant really tell any difference in the engine behavior. I always run the 7 on 98/99 as it has less bioethanol in it. The limited miles I do I can put up with the extra cost!
I have tried the higher octane fuels in my 1600 K and as expected there is no noticeable difference. I have wondered if it could be justified by the supposedly better additives but I generally don't do short journeys in the 7 so don't bother.
Back in the 1950s my Dad's cousin was stationed at RAF St Eval in Cornwall where they had ASR Lancasters... he used to run his Austin 7 on aviation 100 octane which i am told had sparks flying from the exhaust! Probably didn't do the valves much good either...
Probably not much help to the OP (sorry), but I thought some would find it amusing!
In the 1970s when 5 star petrol was still available it was 101 0ctane I seem to recall. I used to run my modified Austin 1300GT on this. It would pink on lesser fuels when driven hard.
I also seem to recall seeing a review of premium fuels a few years ago. Although they all had the correct octane rating some were better than others with regard to calorific value. The one that came top was Shell Optimax (now V-Power)
1985 S3 1700 XFlow. Undergoing full restoration
Democratic dissent is not disloyalty, it is a positive civic duty
It makes a big difference to the R1 at higher elevations. In the mountains in Spain, unless filled with high octane, the engine struggles at low rpm. It's on carbs and I guess with injection engines the ECU compensates for air density.
GJT, that might actually be an indication that your carbs need setting up. I don't know the spec of your engine, but the standard Supersprint jetting often leads to stumbling at low revs and throttle. I can't be certain of course, but if it's not spot on a different brand of fuel might just be enough to highlight this.