The way it works is that an increase in power means the engine has to work less to achieve similar performance in addition theoretically it is using less fuel for that performance, manufacturers scale engine performance to suit all conditions and outright performance is not one of those conditions as reliability has to be factored in, aftermarket tuners use the opportunity to fill in areas where extra performance gains can be made again they also have to factor in a certain amount of reliability as customers would not take to kindly to find gaining extra power resulted in a short lived engine,
My friend, this is not true at all, increase in power first of all means more fuel, not just more air, if you make the mix poor with more air than fuel, in order to claim savings in fuel, then the engine will soon fail. Simple as that.
No tuner can achieve more power gain with less fuel consumption without risking engine life. Simple as that.
Don't be fooled with what tuners are promising, they all want to sell their product, that's why they NEVER give you a straightforward engine or parts warranty nor do they promise in writing any fuel savings and engine warranty (and where they do offer a warranty its so limited and under so many conditions that in reality it can never be materialized) , its all talk and promotion al for people who actually believe that, or for people who want to believe something like that.. Only ABT does it, limited though and in conjunctions with VAG, but with modest modifications and without promising any fuel savings, to the contrary, note the below from ABT:
QUOTE
Fuel consumption and CO2 emissions data for the
CUPRA Formentor VZ3 x ABT Sportsline collaboration vehicle is not available as official testing does not factor in accessories fitted post-registration (such as the ABT pack). Fuel consumption and CO2 emissions data provided is for the standard
CUPRA Formentor VZ3 model. Actual MPG figures for the
CUPRA Formentor VZ3 x ABT Sportsline collaboration vehicle are likely to be lower and CO2 emissions figures are likely to be higher than the values stated.
UNQUOTE
If ABT says that, then you can easily figure out why other tuners are misleading you and lie about it.
Moreover, see the ABT warranty conditions, just to have an idea, what such a warranty is and what really covers so that you are not fooled and be expecting a factory like warranty.
www.abt-sportsline.com