Turbochargers
Parts, specs and what fits what.
Parts
Center section (CHRA)
Center housing rotating assembly. Holds the bearings. Oil in on top, out the bottom, water ports on many.
A/R and trim
A/R 0.63
A: passage area. R: distance from its center to the shaft.
Middle: typical street choice.
Trim 52
Air enters at the inducer, leaves at the exducer. Turbine wheels are reversed.
- Spool
- The turbo speeding up.
- Boost threshold
- Lowest rpm that makes real boost at full throttle.
- Lag
- Delay from throttle to boost, above the threshold.
- Pressure ratio
- Absolute outlet ÷ inlet pressure. 14.5 psi boost ≈ 2.0.
- Surge
- Too little flow for the pressure. Air backs up and flutters. Hard on bearings.
- Choke
- Max flow. Efficiency drops, intake temps climb.
- Trim
- (inducer ÷ exducer)² × 100. Higher flows more.
- Frame size
- Family: T25, T3, GT28, TD04. Parts swap within one.
- Blow-off valve
- Vents intake boost when the throttle shuts. Doesn't limit boost.
Sizing
Left of the surge line: too big. Past choke: too small.
On the map from 4000 rpm. 52% of its flow at redline.
24.0 lb/min at redline, about 240 hp. PR 1.82.
Approximate maps. Check the maker's map before buying. Compressor only; the turbine sets spool.
T3/T4 hybrid
- T04 compressor on a T3 core and T3 turbine.
- More air than a T3, spools sooner than a T4, bolts to a T3 manifold.
- The name says what fits, not how big. Check trim and A/R.
- T04B and T04E are the compressor housings. T04E takes bigger wheels.
Turbo names
- GT
- Garrett GT family.
- 28
- Turbine frame size (GT28).
- 71
- Compressor exducer, about 71 mm.
- R
- Ball bearing.
Bearings and cooling
- Oil
- Every turbo. Drain by gravity: large, straight, downhill.
- Oil + water
- Coolant stops oil cooking in the bearings after shutdown. Plumb the ports.
- Oil restrictor
- Usually needed on ball bearing cores. Too much pressure smokes past the seals.
Wastegates
Gate open: holding 7 psi.
- Internal
- Flapper in the turbine housing. Simple. Can creep boost at high power.
- External
- Valve on the manifold. Steadier boost. Needs a gate port and a gateless housing.
- Spring pressure
- Minimum boost. A boost controller holds the gate shut for more.
- Electronic actuator
- Motor instead of a spring. The ECU sets gate position.
Flanges
Inlet bolts to the manifold, outlet to the downpipe. Inlets drawn to scale.
T3 + T25
Bolt holes overlap. Only works with slotted holes.
- Bolts across
- 86 vs 73 mm
- Bolts up/down
- 44.5 vs 40 mm
- Hole offset
- 6.5 mm (0.26 in), 2.25 mm (0.09 in)
- 5-bolt outlet
- T25, GT28, T3.
- V-band outlet
- GT30, GTX, G series, most new housings.
- Divided inlet
- Twin-scroll. Quicker spool with a divided manifold.
- Car-specific
- Factory turbos (TD04, IHI). Fit their own car only.
Build a turbo
Pick a part. Green fits it, amber needs an adapter, dimmed doesn't fit.
Bolts together
T3/T4 hybrid, T04E 57 trim
- Bearing
- Journal
- Cooling
- Oil
- Compressor
- T04E 57 trim, about 46 lb/min (~460 hp)
- Turbine
- T3, 0.63 A/R
- Inlet flange
- T3
- Outlet flange
- 5-bolt
- Wastegate
- Internal
- Compressor to coreFits with a T04 backplate. This makes it a T3/T4 hybrid.
- Turbine housing to coreT3 housing on a T3 turbine wheel.
- Inlet flange to manifoldT3 to T3.
- Outlet flange to downpipe5-bolt to 5-bolt.
- WastegateInternal gate in the housing.
Common families only. Turbo listing