So, the 1st modification (and most interesting) contributing to this improvement is the sequel from
here
It's actually the 1st "big" project for the clio
RAM AIR Intake Part1 (aka cold air intake)
When I bought the car it had a K&N air filter without the airbox but using the factory S shaped hose.
As mentioned before I had changed the hose to a silicone 45o for better filter placement and less flow restriction.
But I knew that, engine was basically sucking hot air from the radiator.
Also even before buying the car I was imagining a RAM AIR from the 2 small parallel grilles under the front lights.
This was even a reason for selecting ph1.
So, I started a long trial and error, designing and printing, procedure for a scoop which would fit behind the grilles, go under the headlight and come behind them with fresh air, that should eventually feed a custom sealed airbox and as a result provide some pressure at high speeds.
Version7 was almost exactly what I needed for some good tests, so I paused the improving procedure.
I also found a small bucket, cut a hole and passed the air hose in such a way that the filter would only suck air from the front and not it's sides.
This is a temporary solution only for evaluating cold air effect without any ram effect.
The car felt instantly different, more alive and fast.
The base 60-140 (with 3rd gear) time of 10.6s, went easily down to 10.2 which is a 4% improvement, which I consider huge (a full custom tuned exhaust system may not show such improvement alone)
I even did some tests, where I was changing again and again the configuration without leaving the testing area so that no doubt was left.
0-100 went from 6.8 mentioned
here to 6.5 which I consider good, while spinning during launch started being an issue.
Main conclusion is that, a free filter in the engine bay is not only "not as good" as an airbox, it's actually bad.
This also explains the not so good 0-100 time before. Now I'm happy with the current performance.
Only modification needed to other parts, was some trimming to the headlight mount.
Other current improvements and RAM AIR part 2 coming...