My opinion - in days gone by you might have found an engine where the throttle body or some other ancillary component was the weakest link.
These days, engine designers have access to much better simulation tools and testing facilities. In addition, emissions requirements force them to keep gas flow velocities high through the throttle, manifolds and ports, so they will tend to design an engine at a particular power output and you'll find everything is sized to top out at about the same level of tune.
This means, IMHO, to get anything significant out of a naturally aspirated engine, you might as well start again with cams, ported head, maybe larger valves, etc. By that time, you might as well replace the engine management with one you can map properly yourself.
The days of bolt on accessories that will give you power increases are gone (they were only really there in marketing BS). You might gain a bit by remapping with a slightly less conservative ignition map and a tweak at the fuelling at WOT but the cost is likely to make it pointless unless you have an older ECU that can be chipped.
The exception to this is the odd engine, such as the 2.5/2.6, where the engine was probably detuned by fitting quite mild cams to position it in the market, and forced induction engines, of course, where the rules are radically different.
Changing parameters such as injector flow rate and fuel pressure on an original equipment management system just throws away all the work that was put in by the manufacturer to refine the system. You'll just end up with something that does everything badly, IMHO.
As the ex owner of a tuned 2.6 traditional porting and cams did make a noticable difference, I would guess around 20bhp but not more.
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Topic: What BHP to expect....? (Read 7981 times)