First of all, welcome from NW Blighty ..
OK - So I like talking to myself, you get better answers.?
JB seems to be talking to himself too.....
Always useful to update your profile so people know where you are and what car you have.
So what do the experts have to say about FSE's ? For the rest of the world, that's the UK acronym for the aftermarket fuel pressure regulator valve that you can buy and plug into the fuel rail and allegedly gives more fuel pressure (at the expense of a rich mixture and less mpg) and hence more power under acceleration ?
Increasing fuel pressure will result in greater fuel flow through the injector at a given pulse width. In open-loop mode (usually only happens at full throttle and in current generation engines increasingly doesn't happen at all) this will cause a richer mixture which may
lead to an increase in torque/power, depending on how the engine is mapped. There would be a little more charge cooling, so this is usually a good thing.
As soon as the ECU changes back to closed-loop mode, any nominaly increase in fuel delivery caused by higher rail pressure, will be adjusted out by a reduction in injector pulse width.
Generally with engine tuning, the main challenge is getting more air molecules into the cylinder. This is why turbo/super charging is so effective and why fitting high lift cams with more overlap is common in racing engines. Getting more fuel in is easy.
The next challenge having got more air and fuel in, is achieving a controlled combustion to take advantage of the extra energy available.
Then hopefully the manufacturer has built in some additional mechanical strength in the bottom-end and extra cooling capacity.
With modern vehicles that are optimised around the prevailing emissions regulations, and fuel economy/CO2 footprint, there isn't much spare capacity in the engine design. This is borne out by the trend towards higher power density, where 100hp/litre is not as uncommon as it once was in production car engines.
You may have some spare in your 320, but I'd be surprised if there was much in the way of real performance benefits from a simple remap.
These guys claim 13hp increase...