The Mitsubishi Sirius or 4G6/4D6 engine is the name of one of Mitsubishi Motors' four series of inline-four automobile engines, along with Astron, Orion, and Saturn.

The 4G6 gasoline engines were the favoured performance variant for Mitsubishi. The 4G61T powered their Colt Turbo, while the 4G63T, first introduced in the 1980 Lancer EX 2000 Turbo, a non 4g63 variant also saw service in the Sapporo and Starion coupés during the so-called "turbo era" of the 1980s, creating for itself an illustrious motorsport heritage as the powerplant under the hood of the World Rally Championship-winning Lancer Evolution. A UK-market Evo known as the FQ400 had a 400 bhp (298 kW; 406 PS) version of the Sirius, making it the most powerful car ever sold by Mitsubishi.

The 4D6 diesel engines supplemented the larger 4D5. Bore pitch is 93 mm.

The 4G61 displaces 1,595 cc (1.6 L) with bore/ full length stroke of 82.3 mm × 75 mm (3.24 in × 2.95 in). This engine was always DOHC 16-valve and used either Multi-point (MPFI) or Electronic Control (ECFI) fuel injection. A turbocharged version was also produced for the Mirage and Lancer. Unlike the other Sirius motors, the 4G61 does not have balance shafts.

  (late) 160 PS (118 kW; 158 hp) at 6000 rpm and 221 N⋅m (163 lb⋅ft) of torque at 2500 rpm.

The larger 1.8 L 4G62 was an SOHC 8-valve unit for longitudinal rear-wheel drive and all-wheel drive use. With a bore and stroke of 80.6 mm × 88 mm (3.17 in × 3.46 in), it displaces 1,795 cc (1.8 L). It was available either in carburetor form, multi-point fuel injection, or ECI Turbo as found in the Lancer EX 1800GSR or 1800GT, and Cordia GSR.

Turbocharged version of the 4G62

The 4G63 was a 1,997 cc (2.0 L) version.