Mitsubishi 4G6

The 2.0 and 2.4 litre four that carried Mitsubishi for three decades, and in turbocharged 4G63T form the engine of the Lancer Evolution I through IX — one of the most celebrated and most heavily modified engines ever built.

It is an iron-block, belt-driven design, and the iron block is exactly why it became a tuning staple: it tolerates boost far beyond standard. That popularity is also the diagnostic complication. A very large share of surviving 4G63Ts are modified, so the first question on a knock, misfire or boost complaint is what the car is actually running, before any component is suspected.

In standard form the recurring items are the timing belt — an interference design, so a snapped belt is terminal — the balance shaft belt, whose failure can take the timing belt with it, and crankshaft position sensor wear. On the naturally aspirated 4G64 and 4G69 in ordinary cars, the profile is that of any older simple engine: sensors, coils and vacuum leaks.