Mk2 Fiesta Engine Swap Guide: Zetec, Duratec and Cosworth YB for Kit Cars

ByKenji Alvarez

Start with the Zetec — here’s why

Of the three engines people commonly drop into Mk2 Fiesta-based builds, the Zetec is the one that fits without cutting the shell. Two of the three CVH engine mount bolt holes line up with the Zetec; you weld a small extension piece to sort the third. That’s the extent of the mount fabrication on the engine side.

The gearbox is where it gets genuinely convenient. The BC five-speed — the unit that came in the Mk2 XR2 — uses the same bolt pattern as the Zetec bellhousing and bolts straight on. The IB5 is a direct replacement for the BC box if you want something stronger, and switching to an IB5 lets you retain your existing clutch cable, driveshafts and gear linkage. One detail to get right: you’ll need the flywheel, clutch cover and friction plate from a Silvertop 1.8 Escort Zetec rather than a Mondeo unit. The Mondeo flywheel doesn’t match the BC input shaft. Get that right from the start and you avoid an annoying teardown later.

Which Zetec variant?

The 1.8 Silvertop and 2.0 Blacktop are the two you’ll most commonly see used this way. The Blacktop has a slightly higher compression ratio and makes a touch more power in standard form, but in a build running individual throttle bodies and a standalone map the gap is irrelevant — you’ll tune past it either way. Both share the same bellhousing bolt pattern for the BC and IB5 gearbox, so the choice comes down to what you can source in good condition.

ITB support for the Zetec is excellent and well documented. Omex sell complete standalone ECU packages — ECU, harness and sensors — specifically for Silvertop and Blacktop Zetecs on individual throttle bodies, with Jenvey DCOE-style bodies available as part of the bundle. danST Engineering offer DCOE-style kits in multiple bore sizes that bolt direct to the head. Base maps are freely available online, and there are enough people running this combination that you won’t be troubleshooting in the dark.

Ford Duratec: better head, harder installation

The Duratec flows better from the factory and ITB kits are well catered for — Jenvey, danST and AT Power all supply complete packages, and Omex produces a Duratec-specific standalone ECU option. From an induction and management point of view, it’s a strong base for this kind of build.

The difficulty is the gearbox. The Duratec uses a Mazda-derived bellhousing bolt pattern, not the Ford BC pattern. Your BC or IB5 box won’t mate to it directly. Most Duratec conversions use a gearbox from the Mazda-sourced application family, and those typically want a hydraulic clutch rather than a cable — so your existing clutch cable setup doesn’t carry over. The upper engine mount also needs more fabrication than a Zetec install requires.

None of that is insurmountable in a kit car context. But if keeping fabrication down and retaining the cable clutch and standard linkage is the priority, the Duratec costs you more time and money to get to the same starting point. If you’re building from scratch and the extra head flow matters to you, it becomes a more interesting proposition.

Cosworth YB: it has been done, but it’s a project in itself

The YB has ended up in Mk2 Fiestas and Fiesta-based kit cars. There are build threads, and a handful of specialists have fabricated dedicated mount kits for it. But this is a longitudinally-mounted, rear-wheel-drive turbocharged engine being placed in a bay designed around a transverse FWD unit — and the amount of work reflects that. Expect custom mounts front and rear, a complete rethink of the clutch and drivetrain layout, and a serious number of fabrication hours.

Engine sourcing is worth considering too. YB units in decent condition have become harder to find, and prices have moved accordingly. Rebuild and parts costs follow the same curve. For a car that sees regular use rather than occasional outings, that’s worth factoring in before you commit.

As a deliberate design choice in a purpose-built kit car with no constraints on fabrication budget, the YB makes sense. As a relatively straightforward CVH replacement in a car with standard Mk2 mounts, cable clutch and factory gear linkage — it isn’t that.

Quick comparison

  • Zetec (1.8 Silvertop / 2.0 Blacktop): Closest to a bolt-in swap. Minor mount modification, BC or IB5 gearbox bolts up, clutch cable and gear linkage carry over. Huge aftermarket for ITBs and standalone management. Best option for minimal fabrication.
  • Duratec (2.0 / 2.3): Better flowing head and excellent ITB support. Requires more mount work and a gearbox change; hydraulic clutch likely needed. Worth it in a ground-up build.
  • Cosworth YB: High reward, high effort. Custom mounts, custom drivetrain, specialist knowledge. Engine sourcing is getting harder. Only makes sense as a deliberate feature of the build, not a convenient CVH substitute.

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