In reply to GrahamD:
> (In reply to thebrookster)
>
> Thats what I thought, which was why I was curious about the OP's statement:
>
> "Initially performance AND economy noticably increased"
Aah, there you start getting into the nitty gritty, and things become a bit more complex.
Whilst increasing the performance of an engine as a rule reduces economy, it also depends on factors such as the car itself. For example, you might have a Fiesta with a 1l engine, and another with a 1.4l engine. Most people would automatically assume the 1l is more economic, but this really depends on usage. Say you carry yourself, a passenger and some luggage, this would mean the 1l has to be pushed to reach an efficient cruising speed. The bigger engine, however, can reach the same cruising speed far faster with a lot more ease. Therefore the 1.4 can suddenly become more efficient.
You also have to factor in where fuel is needed. A fuel "map" is quite a complex item, as it has to take into account what the engine is doing. An accelerating engine will require far more fuel at 2500rpm than a engine cruising at 2500rpm, and deccelerating requires hardly any fuel at all. Adding this chip will affect all the sections without discretion, so it may well give better fueling for acceleration, yet move cruising fuel to a more efficient value.
Also, driving style has to be factored in. The OP possibly still drives exactly the same as he always did. Lets say for argument he uses each gear, and changes religiously at 4000rpm, until he reaches his criusing speed of 70mph in top gear. Chipping his car gives more power, meaning his engine revs to 4000rpm faster. This means he accelerates faster than before, so he reaches his cruising speed far faster, and spends longer at the efficient cruising speed as a result. This will also translate to a better economy.