It is not Boost. It is where in the RPM the torque is generated. The stock turbo is right at it’s pinnacle of getting out of efficiency even at 21psi. Harder to control the torque with the stock turbo due to its inability to expel exhaust efficiently enough; thus, torque generation
With a slightly larger turbo the torque can be controlled better and achieve more power on less boost w/o generating as much heat.
Since you are seemingly not custom tuned, stick with your KTuner Maps and don’t finagle with the Boost Tables
I've targeted 26psi before. Not worth it on the base model turbo, probably even the Si isn't too much better at that pressure. My current tune is good for 22-23psi. I've run a homemade tune that gets me mid 24psi. I have a few variations of it. They're good for straight-line, but I need to work on it some more for smoother drivability. I'm also planning to use the ECON Button as my hobo launch control.
IIRC these are my targets for that 24psi tune...
Slot 1 Normal: ~17.5psi (I have the boost for high load/throttle conditions; this is for local roads)
Slot 1 ECON: ~16psi (but I have to wring it out with rpms, keeping it 'econ')
Slot 2 Normal: ~21psi (comes on stronger than 1, focus on take-off and mid-range)
Slot 2 ECON: ~18psi (drives like more performant stock 'Normal'; gets better mpg too)
Slot 3 Normal: ~+24psi (increased redline let's it do what it'll do up top)
Slot 3 ECON: ~21psi
My fastest quarter time was on Slot 2 of an early version of this 24psi set of tunes. It had 21-22psi for that.
I'm considering upgrading the turbo inlet and intercooler (maybe just the charge pipes). I don't see much of a differential on the TC Pressure and the Manifold Pressure. But I imagine removing the charge pipe flexing and any restriction on the inlet to the turbo could improve performance by maintaining and aiding the boost being generated.
It isn't the Turbo Inlet that is a restriction. A simple drop-in high flow filter would provide plenty of volume and velocity (on the stock box). Your boost is being generated by "torque" targeting, so if you really want to make the best of the small snail then a free flowing DP would provide that. I am not taking away from the fact that the stock DP is fine in of itself; I am simply trying to supplement what you are trying to achieve.
Do understand that even with improved intercoolers and running the PSI you are on MAP 2 & 3 that once you get "off" of throttle your IAT2 will increase ever so slightly until you begin to ram another jet stream through it. As long as you are in boost the improved intercooler will keep temps better, it's when you get off (and idle or slow) and try to get back on that you have to wait for the increased temperature to dissipate. Just the nature of a very small turbo.
Keep in mind that the Si turbo does about 16-17% better at expelling exhaust gasses - that's why the Si is more responsive and capable of handling more PSI.
Also: If you want an optimum tune, then get with a reputable tuner and tune in for a Higher Octane (like 95Oct using some race fuel) if you want 1/4 mile times? With the stock turbo you won't achieve the balance of having the low/mid and high RPM power. You will need to settle of which set-up you prefer or get another turbo. But, if you are on a CVT I wouldn't suggest it - since that is yet an addt'l restriction.
I will admit, that adding an improved turbo would provide for better response and open up more RPM range - but, when it comes to tuning you won't take advantage of its full capability on a CVT. You would require less boost and run cooler and be more consistant. On demand power is always appreciated right? But, you have to decide the benefits over the cost.