The Heart of the Beast: Understanding the FA20 D-4S

As mentioned in my previous post, Toyota reached out to Subaru to ask them to produce the GT86's (and BRZ's) power-plant, the FA20. The reason Toyota decided to do this was because Subaru had been successfully designing flat four boxer engines for many years, having implemented tuned and souped-up specs into their rally cars as well as standard naturally aspirated versions in their road cars. Toyota desired to obtain one of these flat four boxer engines to fit in their engine bay due to the possibility of having as low a centre of gravity as possible with this style of engine. This aids the 86 in its ultra low centre of gravity and near perfect weight balance.

The unique boxer nature of the FA20 means the pistons move horizontally to the car, with two sets of two pistons in pairs. Each pair moves horizontally opposed with symmetrical ignition timings. This design helps reduce vibrations but predominantly aids in keeping a low weight balance as opposed to an inline four engine, with pistons moving vertically, taking up a lot of vertical space in engine bays - giving a much higher centre of gravity on the front end of the car. This design helps enhance stability and handling vastly - allowing the 86 to have a lower centre of gravity than a Ferrari 458.

The engine is only 2.0 litres, perhaps quite small for today's standards in a sports car putting out a measly sub 200bhp and 151 pounds of torque, however, it allows the driver to use all the power band with a torque dip seen between 3000-4000 revs forcing the driver to use those higher exhilarating RPMS to stay in power while driving. 

Toyota's input into engine development was seen with its then new D-4s direct injection. This created a major challenge in engine development in that when fuel is directly injected into the combustion chamber it is a much tighter gap than fuel being injected into the port and is then further complicated with timing issues to continue working smoothly at high revs. 

An over-square displacement was chosen for the FA20 which is uncommon for cars and more commonly seen in motorbikes, this means the bore is greater in diameter than the stroke length. This commonly sees engines make less power in lower revs, allowing engines to rev higher and produce peak power at much higher revs. With a red line of 7400rpm the FA20 represented a world's first in high revving direct injection and begs to scream!