Tech guide · Engine
Impreza injectors and turbos explained
Two of the most-asked identification questions: which injectors and which turbo does my car have? Here is how to tell, and what was fitted from the factory.
At a glance
Side-feed or top-feed
Classics use side-feed injectors; every Impreza from 2000 uses top-feed.
Read the tag
The turbo model is stamped on the compressor housing tag.
Always remap
Bigger injectors or a different turbo always need a remap.
Injectors
| Car | Type | Size and colour (factory) |
|---|---|---|
| Classic WRX and UK Turbo (most 1993–98 cars) | Side-feed | 380 cc, grey |
| Classic STI, and UK Turbo 1999–2000 | Side-feed | 440 cc, yellow |
| New Age onward (2000–) | Top-feed | Size varies by model: check the part number on the injector body |
- Side-feed and top-feed injectors are not interchangeable without changing the fuel rails.
- Colours only identify factory injectors: aftermarket injectors use their own colours.
- Bigger injectors always need a remap. Never fit them on a standard map.
Turbos
Japanese-market WRX and STI models used IHI “VF” turbos; most UK and European Turbo and WRX models used a Mitsubishi TD04-family turbo. The model is stamped on the compressor housing tag.
| Turbo | Factory fitment | Notes |
|---|---|---|
| VF22 | JDM classic WRX (Version III) | Big compressor: strong top end, slower to spool |
| VF23 | JDM 22B | Ball-bearing |
| VF24 | JDM classic STI (Version IV) | |
| VF28 | JDM classic STI (Version V) | |
| VF29 | JDM classic STI (Version VI) | Similar to the VF24, with a revised compressor wheel |
| VF30 | JDM New Age STI (early) | Single-scroll |
| VF34 | JDM New Age STI Spec C (early) | Same compressor as the VF30 |
| VF37 | JDM Blobeye and Hawkeye STI | Twin-scroll |
| VF36 | JDM Blobeye and Hawkeye Spec C / Type RA | Twin-scroll, lightweight turbine |
| VF42 | JDM S203 and S204 | Twin-scroll |
| VF39, VF43, VF48 | US-market STI (2004–06, 2007, 2008–10) | Single-scroll. Common as cheap used upgrades |
Things to know
- Twin-scroll turbos (VF36, VF37, VF42) need the matching twin-scroll manifold and up-pipe: they do not simply bolt onto a single-scroll car.
- A turbo swap almost always needs a remap. More boost without more fuel is the classic way to melt a piston.
- Signs of a tired turbo: blue smoke on boost, shaft play, oil in the intercooler, or a siren-like whine.
- Used turbos are a gamble: ask for a shaft-play check and, ideally, a photo of the compressor wheel.
More guides
Subaru Impreza turbos explained
Gearboxes, diffs and DCCD
Subaru Impreza service guide
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