The Flat Line
An in-depth look at the 526hp GT350’s 5.2-liter engine hardware
By Steve Turner
Photos by SID297, Tob, and courtesy of Ford Motor Company
Unless you went off the grid this week, you now know that the 5.2-liter engine in the forthcoming 2015 Shelby GT350 will serve up 526 horsepower and 429 lb-ft of torque from the end of its Flat-Plane Crankshaft. Of course, you know that. The Internet already told you. In fact, we were providing live-coverage from Ford’s invitation-only media event on the GT350’s powertrain. And, yeah, we previewed a lot of this stuff right after the North American International Auto Show last January.
While SVTP and every other automotive outlet have already shared the obvious details, we actually had boots on the ground in Allen Park, Michigan. Our team was able to spend some time speaking with the engineers that created this internal-combustion masterpiece (see the full presentation video at the end of this story), and after surviving the initial rush of information, we were able to sift through our notes and uncover a few more of those technical details that we know loyal SVTP Front Page readers with appreciate about this engine.
“Our mission was to create the ultimate engine for a track going Mustang. That meant light weight, high specific power, a broad torque curve, and amazing throttle response,” Jamal Hameedi, Ford Performance Chief Engineer, said. “Hopefully we came up with something that will live up to the legend of the original 289, which was an amazing engine.”
Certainly the 289 was an impressive performer for its day, but it was born of a time when engineers had to borrow parts from other programs, modify parts off the shelf or wait for prototypes to be created. The FPC 5.2-liter, codenamed Voodoo, was truly born from the modern magic of computer-aided design.
“Using CAE for complete design of this engine allowed us to deliver this engine in time. The first prototype engine that we produced made of 500 horsepower within one week of getting it on the dyno,” Ford V8 Intake Combustion and Exhaust Technical Specialist Adam Christian explained.
Yes, instead of taking parts off the shelf and trying them, the entire engine was designed inside a computer. The iterative testing took place in the virtual world, and the results of that testing were turned into the parts that created that first engine. And, while the timeline was short for an engine of this magnitude, the project actually got underway about three years ago after the release of the vaunted RoadRunner engine that powered the Boss 302.
“Around the time that the Boss came out and we were all really enjoying our success at about 88 horsepower per liter, that was the time that Ford Performance came to us and said, “Well, that was nice, but we’d really like to have 100 horsepower per liter and we’d really like to have 500 horsepower, and we’d like to spin over 8,000 rpm,’” Adam said. “That’s actually a tough pill for an engineer to swallow, because it basically says, ‘Nice try, but I’d like for you to do even better.’”
The result of Jamal setting the 500 naturally aspirated horsepower target is an engine that is clearly the cousin of the Coyote and RoadRunner 5.0-liter engines. However, the Voodoo 5.2 is said to be something else all together. And, it is definitely better.
“This is a new engine; An all-new engine. Top to bottom throughout the internals, everything that contributes to that power and speed is new.” Engine Program Supervisor Eric Ladner said. “…At first glance people may think it looks like a 5.0-liter. Of course, it is sitting in a similar package, but it’s far from it.”
Beyond another .2 liters of displacement, what sets this engine apart from its predecessors is the implementation of Ford’s patented Plasma Transfer Wire Arc coating in the cylinder bores. Previously implemented on the 5.8-liter Trinity engine in the 2013-2014 Shelby GT500, this process allows for a bigger bore in compact package. The coating is much thinner and lighter than a traditional sleeve, so you can pack in the displacement without packing on the pounds.
The larger 94mm bore created by the PTWA coating not only helps the 5.2-liter engine gain that extra displacement, but it enabled Ford engineers to spread out the valves in the all-new cylinder heads. Spacing them out allowed for valves that are 1mm larger in diameter than the 38.3mm intake and 32.9 exhaust valves found in the 2015 5.0-liter engine. Because the larger bore doesn’t shroud the larger valves, they can really breathe.
Apparently bigger valves want bigger cams, and who doesn’t want bigger cams? As such, this engine’s bumpsticks exceed the 13mm milestone set by the Boss 302 with a whopping 14 mm of lift.
“The valve likes to be lifted a certain amount in ratio to its diameter, so as you go up in diameter, you have to go up in lift if you really want to take full advantage. This engine is absolutely the high watermark for us. It’s 14 mm of lift on a Four-Valve head, which is pretty much unheard of,” Adam explained. “We are talking lift values that you would find in a Two-Valve application. So we are lifting the valves a lot at a high rate of speed with a maintenance-free hydraulic valvetrain. That’s one area we are very aggressive as a company with our valve-lift profiles.”
Of course, valve lift isn’t the only area where the team got aggressive. In setting the 500-horsepower target, Jamal told his engineers to “take the gloves off.” That led to the implementation of the vaunted Flat-Plane Crankshaft.
“Conventional V-8s have a firing order that’s mixed… Certain cylinders fire immediately after each other 90 degrees apart, one a bank. That presents a tuning problem for me, essentially. Each cylinder behaves differently, and they behave differently throughout the speed range,” Adam explained. “We put in the Flat-Plane Crank, and what that does is it makes all the cylinders behave the same. That makes my optimizations much easier. We can tune this engine to within an inch of its life for all cylinders. We don’t have to tune for the best breathing or the worst breathing cylinder. All geometries can be the same, so we can really tune this thing and get the acoustic resonances as high as possible.”
Optimized via computer modeling for Ford’s induction system, the crank in the 5.2-liter engine is gun-drilled to reduce its reciprocating weight. Flat-plane cranks are lighter than their traditional counterpart by nature, but Ford engineers say that working with the dual-mass flywheel and a smaller clutch, this gun-drilled crank accounts for only 15 percent of the engine’s rotational mass. Additionally, its hollow core is said to give up nothing in terms of durability.
Further maximizing the efficiency of this engine is the block the crank resides in. Not only does block feature the aforementioned PTWA cylinder bore liners, but the bores themselves are rounder and stronger. The bulkheads are also more robust than a Coyote block. Ford is applying the PTWA liners in-house these days, and the company is also using the age-old race-engine process of deck-plate honing when the blocks are machined. By torquing head gasket and deck plate to the block to simulate the torque of the heads while the block is machined, the cylinders are rounder.
“When the engine is assembled the bores are as straight as they can be. What that allows us to do is to drop the ring tension,” Adam said. “So we can make the rings in the pistons ever so slightly springy because they don’t try to push as hard against the block to try and conform to a non-round bore. That reduces friction. Forty percent of all mechanical friction in an engine is in the rings themselves.”
Clearly, Ford Performance engineers are squeezing every last drop of efficiency from the 5.2-liter engine. Not only did computer simulations help design an engine that was ready to go right away, but that same kind of computational horsepower helped them tune every aspect of the resultant hardware.
“We bring all that together and actually run millions of simulations to dial in the runner lengths, the diameters, the camshaft durations, and the camshaft phasing,” Adam said. “As you probably know, we have TiVCT on all of our engines. If you look at all the options that gives us for cam timing, that takes the 25-point rpm sweep that we typically run for our power pulls and turns it into 15,000 options for cam timing.”
They certainly dialed in all the variables quite well. The Voodoo engine has a broad, fat torque curve and produces over 100-horsepower per liter. When you consider the base price of the GT3500 comes in under $50,000, this Hummingbird flies in rare air from a performance-for-your-dollar standpoint.
“The whole 5.0-liter family of engines is incredibly knock tolerant compared to others, and it’s because of the work we have done in the combustion chamber and the piston top,” Adam concluded. “We are able to run at optimum spark timing at 12:1 compression on 93-octane pump gas with a port fuel injection system, which is quite rare.”
If you want even more detail on this rare-breed of engine, check out the in-person perspective on the engine media event over on our forum.