06 WRX... 15.5psi boost maxium allowable?

[absubtle]

I was tuning a 06 WRX and trying to raise boost to 17-18PSI. The wastegate maxium duty cylce was at 90%. I also tried to raise target boost D to 21PSI. Changed Initial wastegate duty cycle also. But still only able to produce 15.5psi. It does spool faster, but does fall off rather quick.
Any ideas?
Thanks
Absubtle
CO

[Freon]

The stock TD04 turbo is severely undersized for the 2.5L motor. What you're seeing is not abnormal at all. It really can't run much boost, especially at high RPM. Eventually more boost just means the turbo is blowing hot air, not more air. See if you can find a VF39 take-off from an STI if you want more boost and airflow.

You also might consider a new intercooler to safely support the higher boost and air flow.

[absubtle]

Thanks Freon. I was just wondering if there was a problem on my end... trying to control boost.
Absubtle
CO

[Nuke]

I'm getting about 17psi on mine

Maybe try adjusting your wastegate arm

[Freon]

You can probably get 17-18, but only under 4500rpm, maybe only under 3800rpm. That poor little TD04 has a hard time filling the big 2.5L motor.

Your change in manifold absolute pressure in percent should not be too much more than your change in airflow. If your change in manifold absolute pressure is +5% but your airflow only increases by 2% I would stop there, or maybe even back off.

I.e. at 4000rpm if you change boost from 17 psi to 19psi (about 33psiA to 35psiA), that is a ~6% increase in MAP. If your airflow at 4000rpm only goes up from 190 to 195g/s (~2.5%), that probably means your turbo is already being pushed too far. If you instead go from 190 to 200g/s (5%) that's means you're probably not overruning the capacity of your turbo and/or intercooler.

[06Limited]

GM BCS and a 7.5lb actuator from a earlier WRX. I hit 20-21psi. with a slow taper to 11 at redline.