Wastegate

01

Understand what the wastegate controls

Garrett's installer training notes explain that the wastegate allows a controlled flow of exhaust gas to bypass the turbine wheel. This lets the maker use a smaller A/R turbine housing for maximum turbine acceleration at low engine speed while the valve is closed. At higher engine speed, as the housing approaches its maximum flow, the valve opens and some exhaust merges directly with the exhaust outlet flow, which increases flow capacity and reduces back pressure. In the simplest control circuit a pressure actuator is connected to the compressor outlet by a hose and opens the bypass valve when boost reaches a pre-determined level. [6]

Garrett's Turbo Tech 101 adds that bypassing exhaust reduces the power driving the turbine to match the power needed for a given boost level, and that the wastegate uses boost pressure and spring force to regulate the bypass flow. Some commercial diesel applications use no wastegate at all, a layout called a free-floating turbocharger. [5]

On variable turbine geometry (VTG) turbochargers a wastegate can be added in the same turbine housing. A BorgWarner patent application describes one actuator that moves the guide vanes continuously, with the wastegate starting to open only once the vanes have opened to a set amount; increasing the wastegate opening lets more exhaust bypass the turbine and should decrease the pressurised air to the intake manifold. [8]

02

Choose an internal or external wastegate

Garrett describes external wastegates as regulating turbocharger shaft speed by venting exhaust gas around the turbine stage. Its GVW external wastegates come in 40, 45, 50 and 60 mm valve sizes, with replaceable valve and bushing components for longer service life, an anodised aluminium actuator cover, and springs, fittings, flanges and V-band clamps included. [1]

Garrett's Turbo Tech 101 describes internal wastegates as built into the turbine housing, consisting of a flapper valve, crank arm, rod end and pneumatic actuator, and says this actuator should be connected only to boost pressure because it is not designed to handle vacuum. External wastegates are added to the exhaust manifold or header; their bypassed flow can be reintroduced into the exhaust further downstream of the turbine, which tends to improve turbine performance, and on racing applications it can be vented to atmosphere. [5]

The installer notes describe the internal valve as mounted on an arm that passes through a bush in the turbine housing, with an external crank welded to it and moved by a pneumatic or electric actuator. A pneumatic actuator may be powered by air pressure or vacuum, while an electric actuator responds to commands from the vehicle's engine control unit. [6]

Garrett's comparison lists for external wastegates multiple valve sizes, less manifold backpressure, the option of adding valves for more flow, water cooling and replaceable parts, against a larger size and extra fabrication. For internal wastegates it lists compact, cost-effective and reliable for lower boost, against a small valve with limited flow that cannot be enlarged, slower response, possible overboost in high-flow configurations, and heat build-up in the turbine housing. Garrett offers internal-wastegate turbochargers only up to its G-Series 35 and GTX35 frames; G-Series 40 and GTX40 have externally wastegated turbine housings only. [4]

Turbosmart lists internal wastegate (IWG) actuators matched to specific turbochargers and vehicles, for example models rated 5, 12 and 14 psi, a 26 psi actuator for the Ford Powerstroke 7.3L, vacuum actuators rated 6 inHg, and universal actuators with 57 mm and 76 mm diaphragms. [2]

Give the supplier the engine and turbocharger model, internal or external wastegate, target boost, spring (base) pressure, boost control method, valve size and flange type, exhaust temperature and cooling available, mounting space, and quantity.

03

Set spring pressure, cooling and duty

Garrett gives a standard base pressure of 1 bar (14.5 psi) for its GVW external wastegates, a minimum base pressure of 0.2 bar (3 psi) and alternative spring combinations such as 1.6 bar (23 psi) and 1.7 bar (25 psi) in its spring chart. Liquid-cooled actuator ports for severe applications reduce body temperature by up to 52%, and the diaphragm is thermally optimised for durability. [1]

Garrett describes how the external valve opens. The diaphragm is clamped between the upper and lower actuator caps and forms an air seal; a boost signal port feeds turbo boost beneath the diaphragm, which pushes up against the springs and lifts the valve. With the standard 1 bar (14.5 psi) springs it takes 14.5 psi to fully open the valve, and springs can be changed to as low as 0.2 bar (3 psi) or as high as 1.7 bar (25 psi). The valve caps boost at the combined spring pressure only if it is sized properly. [3] [4]

Editorial calculation: 1 bar is 14.5 psi and 0.2 bar about 2.9 psi, as Garrett lists; a 60 mm valve has about 2.25 times the flow area of a 40 mm valve ((60 ÷ 40)²). [1]

04

Check heat and shaft sealing

A BorgWarner patent on sealing actuator shafts (US 9388732 B2) states that the outside of a turbine housing faces ambient air while its volute surfaces see exhaust gas of 740 °C to 1050 °C depending on fuel, and that the actuator must still move the wastegate in an accurate, repeatable, non-jamming manner. Because there is an annular clearance between the pivot shaft and the bore of its bushing, hot exhaust gas and soot can escape from the pressurised turbine housing through that gap. [7]

The patent explains that the shaft runs in a stationary bushing rather than directly in the turbine housing bore, to better match thermal expansion and so keep close clearances, and to inhibit severe galling between shaft and housing materials. On VTG turbochargers driving exhaust gas recirculation, turbine back pressure can be up to 500 kPa. Escaping gas leaves soot on the outside and carries CO, CO2 and other toxic chemicals that bypass the aftertreatment system; the patent says such leakage is not permitted by engine manufacturers and is a particular concern in ambulances and buses. Its solution is a pair of seal rings biased by a spring to give a continuous gas and soot seal. [7]

Garrett states that its GVW external wastegates have a water-cooling circuit so they can run in very high temperature conditions while keeping their actuation characteristics, and that liquid-cooled actuator ports reduce body temperature by up to 52%. [4] [1]

Ask the supplier how the valve shaft is sealed in its bushing, the maximum exhaust and actuator temperatures, whether cooling is needed, and the service parts for bushing, valve and diaphragm.

05

Find wastegate manufacturers

No manufacturer record has been reviewed for this product yet. Send your specification and CNFX will match it against manufacturer records.

Ask any supplier for valve size and flow, available springs and base pressures, actuator type (pneumatic or electronic), temperature limits, cooling provision, materials of valve, seat and body, flange and clamp type, compatibility with your turbocharger, and service parts.

06

Trace what each part does

This is a functional reference built from the sources cited; it is not one maker's specification.

07

Fill the specification fields with values for your order

A wastegate quotation needs values for your engine. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the supplier.

08

Send the engine, turbo and boost data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Engine: [type; displacement]
Turbo: [model; housing; VTG or fixed]
Type: [internal; external]
Boost: [target; spring base pressure]
Control: [pneumatic pressure or vacuum; electric; controller]
Valve: [size; flange; V-band]
Duty: [exhaust temperature; cooling; shaft sealing]

See manufacturer records Send an enquiry through CNFX