I got fyrther on the shell and it ran better
That wasn't in my head, it was a fact. Tests were done on the same roads at the same speeds
Indicated mpg was 23mpg on tesco iirc and 25.6 on shell. Around town it was between .5 and .9 better. On a long run it could get better than 4mpg better than on tesco.
Testing to 60 was harder, but the fastest i could do ir with tesco fuel was just over 9 seconds, on shell it was down in the very low 8's, the whole engine ran more efficiently.
I resumed the test on other cars slightly, on the calibra there was no difference in performance or economy, bmw no performance diference but better economy, cinq no economy difference but after running tesco fuel for a bit the car felt a bit chocked and slow at the top end, its now on its second full tank of regular shell unleaded and is feeling much quicker at the top end and more eager all round over about 50mph. No figures to back that up but it's not imagination
Seems to depend wildly on the engine tbh, but it tells a story all the negative changes i've found were from tesco fuel
Shell heres no dearer than tesco so unless im on fumes, thats where i go