Your Turbo-Charger has its limits

How do you know when your turbo-charger has reached the limit for output?  Well, we like to break it down into these categories:

  • Heat Soak
  • Wheel Speed
  • Pressure Differential
  • Wastegate Limitations
  • Airflow

Lets talk heat soak for a minute.  It’s most commonly defined as a rapid increase in temperature.  This happens from the compression of air-mass.  As the compression increases, so does heat.  This can be measured by an intake air temperature sensor post intercooler.  Generally we like to see changes in less than 20 degrees F during a pull of BAT.  Sometimes this means reducing the amount of boost run to drop the outlet temperature.  Reducing the heat generated, can allow for more timing and a leaner ARF to be run; thus netting torque and power.  This is how we can make more power on a lower boost level on low octane fuel.  This vehicle on the left is a perfect example of that.  By dropping the boost by 3 psi from the competitors tune, we netted 25awhp.

Wheel speed is one of the best measures to determine if you are over-spinning your turbo-charger.  Since we operate these devices at relatively high RPM’s (100,000+).  The margin for going too fast could simply be 1,000 rpms of speed.  The best way to measure shaft speed is with a wheel speed sensor.  This is a hz based pickup that calculates total wheel speed.  Most EFR turbo’s come with a port ready to read this speed.  You simply add in a hz sampler, and then measure away.

Turbo sizing has a lot to do with our last topics.  Turbo drive pressure, or back pressure prior to the turbine wheel is very important; it also ties in directly with turbo sizing.  Simply a larger exhaust wheel and hot side will bypass more exhaust, thus lowering heat and back pressure.  The inverse is true on smaller turbo-chargers.  This is why there is almost always a trade off between top end power, and spool of the turbo.  Airflow can be easily measured on most cars by tracking the MAFv or calculated air mass.  It corresponds directly to turbocharger size as well.  To get the most out of your turbo charger, get a custom tune today!