Thinking about making a full Intake Manifold Replacement

[cali yaris]

A piggyback system modify existing parameters that are in a ECU. It has limits, On a scale of 1-100 you can only adjust from 35-65. A stand alone allows the user to start from scratch. You can adjust from 1-100. You have full control of fuel & timing. You are not modifing an existing parameter.

I feel a standalone would be needed on a fully built engine, with adjustable boost levels, longer duration cams, bigger valves, these kind of components.

Pistons, rods, adjustable boost levels, bigger valve are not the reasons to go standalone. Full adjustability, safer, more reliable, faster processiing speed, On board data logging, knock control & it makes more power.

If you look at a lot of the tuner cars, you tell me how many of those cars go stand alone.

These are good points.
I have a custom-wired MoTec in my fully-built Scion tC. I did that because the piggybacks didn't give me enough control, as noted above. Last tune netted me 443 whp, 474 torque -- not bad from a 2.4L street car. And more room to go even hotter.

But.... it was friggin' EXPENSIVE to do all that!!

I will never go that far with my Yaris motor....but I hope some people do.