The GA engine is a 1.3 to 1.8 L inline 4

Straight-4

The inline-four engine or straight-four engine is an internal combustion engine with all four cylinders mounted in a straight line, or plane along the crankcase. The single bank of cylinders may be oriented in either a vertical or an inclined plane with all the pistons driving a common crankshaft....

 piston engine from Nissan. It has a cast iron block and an aluminum head. There are SOHC & DOHC versions, 12 valve & 16 valve versions, carbureted, single-point and multi-point injected versions, and versions with variable valve timing

Variable valve timing

In internal combustion engines, variable valve timing , also known as Variable valve actuation , is a generalized term used to describe any mechanism or method that can alter the shape or timing of a valve lift event within an internal combustion engine...

 (GA16DE). The GA was produced from August 1987 through 2007. Since 1998 it was only available from Mexico. In the code of the engine, the first two initials indicate engine class, the two numbers indicate engine displacement, the last two initials indicate induction and head (D=DOHC, S=carburetor, E=injection).
The GA13DS is a DOHC 1.3 litre (1295 cc) engine with a carburetor

Carburetor

A carburetor , carburettor, or carburetter is a device that blends air and fuel for an internal combustion engine. It is sometimes shortened to carb in North America and the United Kingdom....

.