If an automobile engine is described as longitudinal mount, it means that the crankshaft lies parallel to the direction of the vehicle's movement. This is also known as a north-south mount engine. The alternative is the transverse-mount engine.

Longitudinally mounted engines are found reasonably commonly in all types of vehicles, with all combinations of driven wheels, but are most effective in front engine rear drive cars, and four wheel drive cars.

In the case of front engine front drive cars with a longitudinally mounted engine (the Audi 80 for example) the engine is usually mounted quite far forward in the engine bay, with a transaxle setup immediately behind it. In front engine rear drive cars, the gearbox is usually mounted straight onto the back of the engine with a driveshaft running out of it under the length of the car, and into the rear differential. Sometimes (In some Porsches and Alfa Romeos for example) a rear transaxle is used, so the gearbox is at the back, attached directly to the differential.

In motorcycles with a longitudinal mount engine, the rear wheel is usually driven by a driveshaft coming out of the gearbox and into a differential gear built into the hub of the rear wheel itself. BMWs and Moto Guzzis are the most common examples of this.

The primary advantages of longitudinal mount engines include:

• Engine lies down the centreline of the car, providing better left/right weight balance.
• In front engine configurations, differential and gearbox can be mounted further back in the car, providing better front/rear weight balance.
• Gearbox is mounted on centreline of car, further assisting left/right weight balance.
• In rear-drive only configurations, CV joints aren't required.

Disadvantages of longitudinal mount engines include:

• Rotational inertia of the engine can upset left/right stability of a vehicle, and with heavier engines can cause lateral shake while the car is idling.
• Slant engine configurations can sometimes disturb left/right weight balance of a car.
• Cars need a longer nose to accommodate engine length, especially in in-line engine configurations.
• In motorcycles, a rear differential is required, adding weight and complexity to the system.
• In motorcycles with boxer or v engine configurations, cylinder heads can protrude quite far from the body of the bike.
• In four wheel drive cars, engine must be mounted quite far forward in the car to allow the gearbox to drive the front wheels