Ok, so I've been using Vpower exclusively now for the last 5000 miles. Safe to say that the ecu will have fully adjusted to the different fuel and have been pretty happy to pay the extra as the car felt a little bit sharper, quieter, smoother and the mpg went up a couple of miles meening it wasn't costing me any more on fuel month to month anyway.
Thing is, i got caught short last week with the car running on fumes so had to put in £20 of standard derv. Straight away throttle response felt poor and performance was just sluggish. Also the fuel economy dropped and the engine felt a little rough when cold. At first I was thinking that there was a problem, maybe there was something else causing this.
Anyway, filled up the other day with vpower again and after about half a tank used car is back to normal. Better throttle response, the difference is very noticeable and engine feels smoother.
So thinking about this I have 3 theories on what caused this.
1. Because the ecu and fully adjusted to vpower it wasn't too happy when i put standard stuff in (shell) and rewarded me with crap throttle response and general sluggishness. ( as you can see this is very scientific thinking
2. There was some other problem, maybe a bit of crappy fuel at the bottom of the tank which got in to the fuel lines and caused reduced performance.
3. The standard derv i put in was a bad batch and once the Vpower had flushed it all out the performance returned.
I like to think it was theory no.1, and that given time to allow the ecu to fully adjust to the better fuel vpower is actually very good and worth every penny! I know a lot of you will think i'm a bit soft in the head but i'm convinced.