How to Calculate a Turbo’s Trim

Garrett_rotating_group_enlarged

Simply:

trim = inducer²/exducer² * 100

ex. take a TD05H-20g compressor wheel:
inducer diameter: 52.56mm
exducer diameter: 68.01mm
trim: ?

trim = (52.56mm)² / (68.01mm)² * 100
= 2762.5536 / 4625.3601 * 100
= 59.7…
~= 60

ex. take the turbine of a Garrett GTX2867R where Garrett doesn’t list the inducer diameter
inducer: ?
exducer: 53.8mm
trim : 76

76 = inducer²/(53.8mm)² * 100
=> 76 / 100 = inducer² / 2894.44mm²
=> .76 * 2894.44mm² = inducer²
=> inducer = sqrt(2199.7744mm²)
=? inducer = 46.9mm