What is turbo trim and how is it calculated?

Turbo trim is an area ratio describing the relationship between the inducer and exducer diameters of a wheel. Compressor Trim = (Inducer² / Exducer²) × 100. Turbine Trim = (Exducer² / Inducer²) × 100.

What is the difference between compressor inducer and exducer?

For a compressor wheel, the inducer is the smaller inlet diameter where ambient air enters, while the exducer is the larger base diameter where compressed air exits into the housing scroll.

How does turbo trim affect performance and spool time?

A larger compressor trim flows more peak air for higher horsepower but narrows the surge margin and can slightly delay spool. A smaller trim spools quicker and resists low-RPM surge at the cost of top-end airflow.

Compressor & Turbine Wheel Geometry

Turbocharger Trim Calculator

Calculate exact compressor or turbine wheel trim, inducer, exducer, area ratios, and estimated flow capability in millimeters and inches.

Wheel:

Units:

Wheel Dimensions & Target

Calculate:

Inducer Diameter (Air Inlet) * Minor / Inlet Tip

Exducer Diameter (Base Outlet) * Major / Base Edge

Compressor Wheel Trim Formula:

Trim = (Inducer² / Exducer²) × 100

Describes the inlet-to-outlet area ratio. Higher trim flows more top-end air at higher engine RPM.

Calculated Wheel Specifications

Wheel Trim

56.0

Area Ratio %

Area Ratio

0.560

A_in / A_ex

Diameter Ratio

0.748

D1 / D2

Est. Flow

52-55

lb/min

Physical Dimensions

Inducer: 57.0 mm (2.244 in)

Exducer: 76.2 mm (3.000 in)

Inducer Area: 2,551.8 mm²

Exducer Area: 4,560.4 mm²

Performance Character

Est. Power: 520 – 550 HP

Spool & Lag: Fast Response

Surge Margin: Broad Operating Range

Engine Sizing: 2.0L – 3.0L Gasoline

Wheel Geometry Cross-Section

56 Trim Compressor

A 57.0 mm inducer with a 76.2 mm exducer produces a 56 Trim compressor wheel with a 0.560 area ratio.

Popular Turbocharger Wheel Trims

Standard OEM & Aftermarket

Turbo Model	Wheel Side	Inducer	Exducer	Trim	Est. Flow	Max Rating
Garrett GT2860R	Compressor	47.2 mm	60.0 mm	62 Trim	35 lb/min	360 HP
Garrett GTX2867R	Compressor	49.7 mm	67.4 mm	54 Trim	48 lb/min	500 HP
Garrett GT3076R	Compressor	57.0 mm	76.2 mm	56 Trim	53 lb/min	550 HP
Garrett GTX3582R	Compressor	65.7 mm	82.5 mm	64 Trim	75 lb/min	750 HP
BorgWarner EFR 7163	Compressor	57.0 mm	71.0 mm	64 Trim	60 lb/min	600 HP
BorgWarner EFR 8374	Compressor	62.0 mm	83.0 mm	56 Trim	79 lb/min	800 HP
Precision PTE 6266	Compressor	62.2 mm	82.0 mm	57 Trim	80 lb/min	800 HP

Trim Questions & Answers

What is the mathematical equation for turbo trim?

For a Compressor Wheel: Trim = (Inducer² / Exducer²) × 100.
For a Turbine Wheel: Trim = (Exducer² / Inducer²) × 100.

How does trim affect spool time versus peak horsepower?

A larger compressor trim (e.g. 60+ Trim) features a larger inducer inlet relative to its base, allowing higher mass airflow for big top-end horsepower, but slightly increases inertia and narrows low-RPM surge margin. A smaller trim (e.g. 50 Trim) spools faster and resists low-RPM surge.

What is the difference between compressor and turbine inducers?

On the compressor (cold side), ambient air enters through the smaller inducer and exits through the larger exducer. On the turbine (hot side), exhaust gas enters the larger inducer and leaves through the smaller exducer into the downpipe.