Head

[cali yaris]

Sorry Loren, but your theory or whatever you are basing your opinions on here (it sure isn't first hand experience with a Yaris or 1NZ motor) aren't valid or correct. And the misinformation you are spreading is, frankly, counter-productive.

As has been mentioned, the limiting factor for making HP on the Yaris is RPM

This is simply untrue.

From simple bolt-on mods (10-20 hp) to fully built turbo motors (300+), the car makes more power without changing the rev limit. I've pushed the motor pretty far now, and at 310+ whp, it STILL doesn't make power over 6000 rpm. Raising the rev limit does not make more horsepower.

If you put engine management on it that will allow you to raise the rev limit and get control of the fuel and spark in the 5-8k range, then you can make more power (assuming the engine holds together)

Incorrect again, from first hand experience.