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How Engineers Developed The Most Potent, Robust Supercharged V-8 Yet—The 760-Horsepower 5.2-Liter Predator
Alone in a dyno cell the Predator is in hibernation. Its core temperature reached zero degrees Fahrenheit. It hungrily awaits its next hunt for horsepower. Suddenly it snarls to life and revs freely to its peak output. Once the 5.2-liter V-8 reaches operating temperature, the engine stops firing and rests until it is chilled again. It endures enumerable deep-thermal tests as well as many high-speed cyclic dyno tests, which run the engine at speed for long durations. All this testing is designed to represent the full life cycle of an engine in the field, and the supercharged 5.2 passed with flying colors, which allowed engineers to finally sign off on those official numbers that you are probably sick of hearing by now — 760 horsepower and 625 lb-ft of torque.
Described as the most "power- and torque-dense supercharged production V-8 engine in the world," the engine, which carries the off-books codename, Predator, underwent a development evolution that led right up until the last moment before the final numbers were realized. In previous model years, the company has announced numbers and augmented them as the program approached to production. This time the engineers held out, and these are the absolute final, SAE-certified numbers.
"We always set internal targets and the targets are driven by what we want to do with vehicle. So that said, you start with the vehicle, what they want for performance targets and then they cascade that back to power, torque, and of course, powertrain-matching with the transmission," Ford Performance Powertrain Manager Patrick Morgan told us. "Our target was over 700, similar to what we stated publicly. And then, we kind of dialed-in an exact number that was just a little bit over 700. Then as the team worked through some details we found some opportunities to overachieve a little bit."
When it comes to your peers, overachievers can be annoying, but for enthusiasts the go-getters in Ford's engineering group are just the type of people you want developing the most powerful street-legal Ford built thus far.
"I think what it does for us is you can get into programs like this, where we kind of cherry-pick the best of the best engineering team so that we can really go fast with the program and we did the engine program basically on vehicle timing which is uncommon," Patrick said. "We were able to overachieve on timing as well, and we did that with use of CAE tools but also with a highly skilled engineering team — the best of the best."
Having previously spent a tour of duty working with NASCAR programs at Ford Performance's Technical Support Center in Concord, North Carolina, Patrick knows a thing or two about using those computer-aided engineering tools to maximize the performance of a vehicle.
"We complete analytical work and then that supports the first phase of testing where we go in and basically prove to ourselves that the analytical work was spot-on," Patrick said. "Usually we find a couple new things. We feed that back to the analytical community so our tools get better, and at the same time we've got to go to work to correct those challenges. We're getting pretty good at that, so we were actually able to pass a number of durability tests during our first phase of development."
The virtual testing gets the team close, and the real-world testing finds those final nuances in need of tweaking and improvement. Combined, these development tools allowed engineers to create the supercharged engine on pace with the creation of the rest of the vehicle, which is unusually quick.
On the dynamometer side we did two full build series; similar to what we do on all major programs. That gives us an opportunity to really dial-in the design. There were a number of significant changes with the crank, connecting rod, piston, block, head, head gaskets, all of the things that you would expect when you are setting up an engine handle 125 bar of firing pressure," Patrick said. "We start with specifying the engine firing pressure and what that pressure curve looks like, and we cascade that out throughout our engineering community. There are a number of a CAE analysis done on the block, crank, bottom-end, bearings, head gaskets and the heads. To make sure everything is capable of handling that kind of pressure. And then there's combustion analysis done and thermal analysis to be sure the cooling system can handle it "
That digital development is done beforehand, wherein engineers build a virtual 5.2 in a computer and adjust its components to achieve its performance and durability targets. These tools continue to get better, and they not only allow engineers to hasten the development process, but find solutions to new challenges.
"We developed a proprietary CAE tool for doing CFD in the crank case, so we can actually look at oil aeration in the crankcase. It's a fantastic tool. We've been using a few years," Patrick shared. "We'll continue to refine it. We correlate it to what we see on track and on dyno. That was one of the key tools that we developed and we continued to refine that allowed us to stay away from dry sump."
The result of that development is an oil pan built to control oil around the pickup and the kinds of high g-loads the GT500 is capable of producing. It includes a perimeter around the pickup and hinged trap doors that allow the oil to move when it should and stay put when it shouldn't.
Engineers also used these tools to strengthen the existing 5.2-liter platform for its duty in a high-pressure boosted environment. It gave them direction on where to beef up the internals to withstand boost and rpm.
"On the connecting rod, we do that analysis and work and our partner does that as well. So you're looking at stronger I-beams. You're looking at stronger big ends. You are making sure the piston pin and the piston interface all work well together so you're not overloading anything," Patrick said. "Then there's some thermal work done there as well to ensure the piston-cooling jets are sized right and the pistons are going to handle the heat load. That carries down through the bearings. We've got copper-lead bearings in this engine, so there they're robust to about anything you could do to them."
In addition to the internals, engineers updated the 5.2 block originally developed for the naturally aspirated GT350 to handle the boost. As a result they added meat to the cylinder bore below the water jacket and added a cast-in brace on the intake side of the bore. They even the reworked the placement of the breathing ports to better allow the block gasses to equalize and minimize windage. Combined with a new four-layer multi-layer-steel head gasket and longer head bolts, the engine is ruggedized to handle sustained operation with 12 pounds of boost.
In particular, returning to the bolt length that debuted on the original naturally aspirated Coyote 5.0-liter engine delivers more stretch and clamping force, and they actually enhanced block durability by moving stress points to more appropriate regions in the casting. Likewise, the CAE simulations led to a fourth layer in the multi-layer steel head gaskets that allows for flexing and lift of the head during high firing pressures while retaining the seal.
"That's true that we had deeper head bolts for a period of time and we were looking for weight opportunities, and for a while it worked well with the Coyote that we could take a little weight out and still have a really robust design," Patrick said. "What we found is we needed to go back to that former design, if you will, because it's just stronger. So we had to take a little bit of a weight penalty there. It wasn't too bad and it was definitely worthwhile with a supercharged engine."
Obviously the blending of virtual design and simulation with real-world testing brought out the best in the combination. Engineers opted to utilize fillet-rolled micro-alloy steel crankshafts of the traditional crossplane variety. The micro-alloy offers manufacturing benefits and the fillet rolling helps it shrug off fatigue. However, they didn't just rely on virtual testing to ensure these cranks were strong enough. They pushed them beyond what they would ever see in the real world.
"We basically break cranks to be sure that we understand what the fillet rolling is capable of doing," Patrick said. "This expanded our database. We actually had to go to a steel and fillet-rolling load that was actually beyond anything we've done in the past. We leveraged some of the knowledge from the industry and demonstrated it for ourselves so that we could go to that next level "
Not only did the block and crank benefit for the CAE analysis, but the cylinder heads did as well. They recast the GT350 head with more meat around the water jackets for better sealing and stronger valve seat material to handle the heat.
"We did upgrade the exhaust valve seats," Patrick said. "Obviously with the higher heat loads we needed to upgrade that a bit and the springs as well. With the added airflow you get a little bit more back pressure and you've got to upgrade things to handle that backpressure and keep the valves closed. Again, all driven by CAE work and verified with testing. In that case we did some track testing as well, and did some pretty clever instrumentation and verified that we had good valve control even on track."
The team of engineers also learned that the upgraded timing chains and lash adjusters once reserved for the GT350R would do the trick in the GT500 as well. Along those lines, this engine gets a forged steel crank sprocket and a more robust oil pump featuring larger gerotor internals made of harder, stronger powdered metal than previous models. The latter came from information share from Ford Performance Parts on the upgrades enthusiast turn to when they are drag-racing high-rpm Coyote engines.
Further reducing stresses on the cam sprocket and the crankshaft itself is the implementation of an aluminum viscous crank damper, which is a point of pride for the team and a new product for its supplier. While the cross-plane crank eliminates the fourth-order harmonics found in an even-fire engine, the virtual tools didn't quite replicate all the stresses of a supercharged engine spinning to 7,500 rpm.
"The CAE said we'd be in control for crank torsionals and we were. We didn't have any crankshaft problems, but we got into some other concerns with the cam drive that had us focus on the crank damper quite a bit," Patrick said. "Our solution was to get rid of some weight and to improve the tuning. A very concerted effort gave us a win-win, with a reduced weight on the nose of the crank, reduced weight on the engine at the front of the car, and at the same time, much better performance from a durability standpoint."
Engineers tear down all the development engines after the testing cycles and the hard parts and gaskets were all in superb shape, so they are quite comfortable releasing 760-horsepower V-8 engine to the public.
"We're really happy with the performance of the engine, durability of the engine on all of our dyno cycles. Then in parallel, you asked about the vehicle testing. We do 24-hour track durability. If you will, you kind of think of an endurance race, and we do the equivalent of that," Patrick elaborated. "The whole car is exercised, really, so we're learning about the whole powertrain. So it's not just the engine, it's the engine and the transmission — the whole driveline. There's some V-max testing, and a number of other durability tasks. Generally speaking, we validate what we've learned analytically, and we do most of our sign-off validation on the engine dynamometer and transmission as well."
The transmission sailed through that testing with flying colors, so the stage is set for an impressive total package on the track and on the street. We are eager to experience the results of this race-bred engineering, but one person who has driven the car is already complementary of the results.
"The 2020 GT500 engine screams to its 7,500-rpm redline with more character and soul than any other production supercharged V-8 that I've driven," Ford Performance racing and development driver Billy Johnson announced on social media. "It's fast."
In fact, thanks to the ingenuity of the Ford Performance engineers and their virtual and real-world development tools, the 2020 Shelby GT500 is definitely built Ford fast.