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What is TRIM or step?


Each turbine wheel and compressor wheel model generally have the same turbine diameter (highest diameter), but different steps (lowest diameter). Each type of step (trim), has different blowing characteristics.

Turbocharger Turbine or Compressor Wheel sketch showing the large diameter Dg and the small step diameter Dp
  • TRIM values are expressed as 45, 50, 55, etc... and can only go from 0 to 100. A value of 100 means Dp is equal to Dg.
  • A large TRIM indicates a large turbine diameter.
  • A TRIM of 55, gives 10% more caudal than a TRIM of 50.
  • TRIM is used in the same way for turbine wheels as for compressor wheels.
  • TRIM is calculated through the following formula:

TRIM = ( Dp / Dg )² x 100

Example: If Dg = 50 mm and Dp = 35 mm
TRIM = ( 35/50 )² x 100 = 49


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