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Quick & Dirty: Understanding Powertrain Configurations

Automotive lingo is filled with a myriad of abbreviations and acronyms; some are commonly known, others are more obscure and many don’t make sense. In this article, we will discuss basic terms concerning engine and drivetrain layouts - where is the engine located and which wheels are driven?

Transverse

A transverse engine layout has the crankshaft perpendicular to the long axis of the car. The benefit of this arrangement is the ability to fit a large engine, such as a V6, and a transmission into a small engine bay. The inline-4 in this Mazdaspeed 3 is mounted transversely.



Longitudinal

When an engine's crankshaft is parallel to the long axis of the vehicle, the motor is said to be mounted longitudinally. This is the setup found in most performance applications, where efficiency of space is not a concern. The V8 in this Audi S5 illustrates a longitudinal layout.



Front-Engine

FF (Front-engine, front-wheel drive)

This one is pretty straightforward; most mass-produced vehicles today use a FF configuration, where the engine and transmission are situated in front of the driver and power the front wheels directly. While this setup allows for cheaper and easier packaging, experiencing the torque steer in a high-horsepower FF car is the best illustration of why this setup is not well-suited for most performance applications. Additionally, FF cars tend to understeer due to how much weight is over the front wheels. Honda Civics, Chevy Cobalts and this Acura Integra are all examples of FF setups.



FR (Front-engine, rear-wheel drive)

FR is considered the classic engine configuration and is the layout found in the vast majority of cars manufactured in the 20th century. As with FF, the engine is located in front of the driver, except now a driveshaft transfers power from the transmission all the way back to the rear wheels. This relieves the front wheels of some of the stress they must endure in FF applications. Some of the best-handling cars in the world are FR configurations, such as the BMW M3, Ferrari 575 Maranello and this Mazda RX-7.



Mid-Engine

Perhaps the ideal powertrain layout, MR vehicles are typically 2-seaters due to packaging constraints. The engine and transmission are located centrally for optimal weight distribution. Much like a FF setup, no long, complicated driveshafts are needed; the axles come straight out of the gearbox to the wheels.

FMR (Front mid-engine, rear-wheel drive)

Cars such as the Honda S2000, while technically front-engine, can be considered mid-engine due to the motor’s proximity to the center of the vehicle. In this S2000, for example, you can see the engine is mounted completely behind the shock towers.



RMR (Rear mid-engine, rear-wheel drive)

Ferrari 8-cylinder road cars, such as the F355, 360 Modena, F430 and this 458 Italia, feature RMR configurations exclusively, a testament to the effectiveness of this design. The central location of the motor keeps the weight where it should be, but with slightly more rear bias.



MF (Mid-engine, front-wheel drive)

Only a handful of older cars, such as this Cord L-29 and certain Citroen and Renault models, utilized the MF layout. This odd arrangement has the transmission in the very front of the car, driving the front wheels, and the engine behind it.



Rear-Engine

RR (Rear-engine, rear-wheel drive)

RR vehicles are fairly uncommon, not to mention much more finicky to drive. With the motor and tranny positioned at or behind the rear axles, even a slight miscalculation at the limits will result in excessive oversteer due to the weight of the engine swinging around in the back. The Porsche 911 is probably the best example of RR, although some of the newer models (e.g. 996 turbo) are available with AWD. The original VW Bugs are also well-known RR vehicles.




4WD (Four-wheel Drive)

Any vehicle which powers all four of its wheels can be considered a 4WD; it is how that power is split and channeled to each wheel under various driving conditions that determines in which applications it will be effective.



AWD (All-wheel drive)

Many passenger vehicles now feature full-time AWD, meaning the system is permanently engaged and is not switched “on” or “off.” Audi’s Quattro system was developed in the 1980s and gave the company what other teams considered an “unfair advantage” due to the effectiveness of AWD in racing applications. Subaru is another company who has predicated itself on AWD. While more drivetrain loss occurs when all four wheels are driven, the gain is extra traction and stability.



RHD (Right-hand Drive)

Although most countries in the world are left-hand drive, Japanese imports have become extremely popular in the United States, and the term RHD has become fairly common. It simply refers to a vehicle where the steering wheel is on the right side of the car rather than the left.





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