The 20hp (also known as the V8) was a car made by Guy Motors between 1919 and 1923.

The 20hp was fitted with a 4072cc V8 engine which had side-valves. The valves entered the cylinders at an angle, replicating the characteristics of an overhead camshaft engine layout. The engine was connected to a four-speed gearbox via a cone clutch. The engine produced 53bhp and the top speed of the car was 55mph (89kmh).

The engine and gearbox were mounted on a sub-frame which floated on spherical joints.A skew gear was fitted to drive a magneto and the dynamo. Twin Zenith carburettors were fitted at first but later the Smith five-jet model was specified.

The chassis was 10ft 10in long and fitted with semi-elliptical leaf-springs all round. The handbrake controlled brakes on the rear wheels and the foot-brake controlled a brake on the transmission (later on it also controlled brakes on the rear wheels too).

The chassis of the 20hp cost £1175 (later reduced to £1095), the bodied tourer cost £1475 (later reduced to £1395).

Only 25 were ever built.