The forgotten Theta III sleeper

A flash tune. The Theta III responds well to more boost and timing on 98, and because it shares the engine family with the i30 Sedan N and Kona N-Line the calibration knowledge already exists. An intake and a turbo-back or catless downpipe come next, but the ECU tune is where the real gains live.

Expect roughly 250-270 kW and a solid bump in midrange torque on 98 with a Stage 1 tune and supporting basics; more with a downpipe and intake. The headline number matters less than the response - it pulls noticeably harder everywhere, but FWD traction means you won't always put it all to the road in the lower gears.

It's quick enough stock to embarrass cars that cost a lot more, so it doesn't need one. But it's a conservative factory calibration with headroom, so a tune is the single biggest value-for-money change you can make.

The wet DCT is the main thing to respect - it's the same unit used across the N range and copes well, but big torque needs a transmission tune to manage clutch clamping and protect it, so do the gearbox calibration alongside the engine. Aftermarket support is thinner than the i30 N, so hardware often gets shared from the wider 2.5T parts catalogue rather than Sonata-specific kit.