Based off the Coyote block, the 5.2L engine in the 2105-2020 is unique to this car. The Ford engineers came up with the idea of creating the most advanced Mustang based on this engine. It is an all aluminum block and heads with dual over head cams and 4 valves per cylinder. But the magic of this engine is the crank is a flat plane. Normally you would find this kind of crank only on very exotic European sports cars or maybe on a race car. Ford calls this engine the Voodoo.
Flat plane crank means the connecting rods are bolted to the crank at a 90 degree intervals. This “evenly spaces the crank pins at 180 degree intervals.”# This allows for a very powerful, naturally aspirated engine with 526 horsepower.
The firing order is also different than the stock Coyote engine. Where the firing order normally alternates between cylinders this one doesn’t. The normal firing order doesn’t alternate between banks (sides) of the engine. The firing order for the stock cross plane crank Coyote engine is 1-8-4-3-6-5-7-2.
Cross Plane Crank 
Flat Plane Crank
The flat plane crank from either end looks flat as compared to the cross plan crank. No matter what the firing order is, the engine will always alternate between the left and right banks of the engine. The firing order of the Ford 2015 flat plane crank is 1-4-5-8-2-3-6-7. This is far more efficient in removing the exhaust gases eliminating the need to alternate the header tubes. And it gives the engine a totally unique sound especially compared to a cross plane engine. A crank set up this way does not require the counterweights making the it much lighter. This allows the crank to spin more freely which is ideal for a high revving engine. It does produce more vibrations though. Flat plane crank engines have a shorter piston stroke which should result in less low end torque. But more air in and more exhaust out yields better horsepower.
This engine is rated at 526 HP @t 7500 rpm. The HP stays level all the way to 8,250 rpm. Torque is 429 lbs.ft. @ 4,750 rpm.
The 1915 Cadillac and Peerless were the first V8 engines with cross plane cranks. In 1923 the Cadillac V8 was the first to use a flat plane crank.
Sources of information:
- MotorTrend: Hear the Shelby GT350’s Flat-Plane Crank V-8 on the Dyno – very cool article with a video of the car on a dyno.
- #One All Cylinders: Quick Tech: Crossplane vs. Flat Plane Crankshafts Explained by David Fuller- very excellent discussion of the differences between the normal cross plane crank and the GT350 flat plane crank.
- HotRod.com: What Is A Flat-Plane Crank? by Brandan Gillogly 11-3-2014
- Car and Driver: 2016 Ford Mustang Shelby GT350 2dr Fastback Features and Specs