The G10 is an inline 3 cylinder engine utilizing aluminum alloy for the block, cylinder head and pistons. The G10 has 1.0 liter of displacement and is equipped with either a carburetor or electronic fuel injection and has an optional turbocharger. It has a single overhead camshaft driving six valves.
A 2.91 in (73.9 mm) bore and 3.03 in (77 mm) stroke give the engine a total of 1.0 L (993 cc/60 in³) of displacement. It produces 48 hp (36 kW) at 5100 rpm and 57 ft·lbf (77 N·m) at 3200 rpm with 9.5:1 compression in the carburated model, 55 hp (41 kW) at 5700 rpm and 58 ft·lbf at 3300 rpm in the fuel injected model.
From 1985 to 1986 the engine used a hemispherical head carbureted design. Later, as fuel injection was mandated, the cylinder head was redesigned to add the additional cooling required. This caused the fuel economy of the engine to suffer. A detuned 49 hp unit was used in the ultra-fuel-efficient Geo Metro XFi model, which delivered as much as 58 miles per gallon.