I remember VBH doing test runs for Fifth Gear with standard and high octane petrol. If I remember correctly it had no effect on some and limited effect on others.
Marginal bhp increases with some and slightly better throttle response but not enough for most people to really notice.
When I had a Focus TD as a commuter car I used Millers additive. Combined octane booster/cleaner. Over a long period of testing I worked out it gave about 25/30 extra miles per tankfull. I did not really notice any power/throttle response changes to set me whooping!Cost saving was £25 per bottle of Millers . Bottle cost about £11 and extra miles over it's use gave £36 saving ( net £25).
Driving was higher motorway cruising than non motorway. About 2/3 of annual mileage.
I tried it previously on a Renault TD but no improvement /saving to make it worthwhile.
It definitely boils down to the ecu/engine design etc.and the ability of the car to adapt.
