A 525 HP 5.2L Dearborn New Idea
Words: Jeff Smith; Photos: Ford Motor Company and Jeff Smith
In the escalating world of high performance, Ford has taken a different path on the way to more horsepower. The headline centers on a brand new 5.2L (315ci) normally aspirated engine that makes 526 horsepower and 429 lb-ft of torque. That’s an amazing 1.67 hp/ci from a normally aspirated 32-valve production engine. To put that in perspective, Ford’s previous best N.A. Mustang effort – the Coyote 5.0L – is rated at 435 hp for 2015 or 1.4 hp/ci. This places the new 5.2L Voodoo engine over 90 horsepower on the up side. How did Ford get there? The quickest path to more horsepower is to just spin the engine faster and that’s exactly what Ford has done. Peak torque occurs at 4,750 rpm but the real news is where peak horsepower happens – 7,500 rpm. Let’s take a look inside this new engine to glean how Ford achieved this amazing accomplishment.
If we start with the engine’s foundation, the first surprise is that the Voodoo is not a just a Coyote engine with a flat crank. Except for the commonality of bore centers, a few minor parts, and the fact that it’s a 90-degree V8, the similarities end right there. Ford calls this engine the Voodoo, but it’s more engineering than witch doctor incantations. Let’s start with the classic horsepower equation: Horsepower = (Torque x RPM) / 5,252. This means that if we tune the engine to produce a given amount of torque at a higher engine speed, the fixed denominator (5,252) will deliver higher horsepower at a higher rpm. Let’s look at an engine making 350 lb-ft of torque at 4,000 rpm. Plug that into the equation and we get 266 horsepower. But take that same 350 lb-ft and plug it into 7,500 rpm and the result is 500 horsepower.
This is not a new concept. Engine builders have been coaxing more reliable rpm and power out of engines since the very first automotive internal combustion engine coughed to life over 120 years ago. What’s exciting is that Ford has created a production engine that will live at 7,500 rpm with a redline at 8,250 rpm. And every gearhead wants to know how they did it.
Starting with the foundation, the block which has been significantly strengthened compared to the basic Mod version. But the big news is the flat plane, 180-degree forged steel crankshaft. This is a rather dramatic divergence is because until now, all V8 domestic engines (excluding Cadillacs and a few others produced before 1924) have always used what is called a two-plane crankshaft. Looking at a dual plane V8 crankshaft from the very end, this design places crank throws at four positions, every 90 degrees creating two opposing planes. The Voodoo engine simplifies this by using a flat, or single plane crank (also dubbed a 180-degree crank) placing four throws opposing the other four. One significant advantage to this approach is a reduction in counterweight mass, making the crank lighter and easier to accelerate. Another advantage is the re-positioned throws create a truly balanced exhaust with even pulses exiting every 90 degrees.
The most dramatic, visceral result of the even firing pulse exhaust note is the easily-identified high-pitched exhaust note scream compared to the growl of domestic V8 engines. With a typical dual plane crankshaft, there are always two adjacent cylinders that fire consecutively on one bank of the engine. This uneven exhaust pulse produces the now-familiar domestic V8 sound. The even, 90-degree firing pulse created by the flat plane crank can be duplicated with a two-pane crankshaft engine, but only if the engine is fitted with a bundle-of-snakes 180-degree header system that ties primary header tubes from opposite sides of the engine. This is both impractical and near impossible to achieve for a production-based engine.
So why is this balanced 90-degree exhaust pulse important? Ford decided that by using the flat plane crank concept – which has been around in racing engines literally since the earliest race engine – they could tune the engine to take advantage of these balanced pulses to make more power. According to Adam Christian, a Ford Intake, Combustion, and Exhaust (ICE) engineer, “A flat plane crank makes all cylinders behave the same.” This means engineers were able to “tune this engine within an inch of its life and we don’t have to protect the best or worst breathing cylinders.” What he means is that in nearly all engines, breathing imbalances between cylinders creates under- and over-achieving cylinders. The spark curve is often limited by the most detonation-sensitive cylinder(s). With truly balanced exhaust pulses (which have a direct effect on intake tuning), extracting more power from the engine is a little easier.
Using a flat-plane crank, an engine fires a cylinder on one bank and then switches to the opposite bank in a consistent right-left-right-left (R-L-R-L-R-L-R-L) cadence. With a traditional V8, the firing pulses do not consistently alternate. As an example, the Coyote’s firing order of 1-5-4-8-6-3-7-2 creates firing pulses of R-L-R-L-L-R-L-R. Plus, there will always be adjacent cylinders on one bank firing only 90 degrees apart, which disrupts the even firing pulses. The Coyote, for example, fires adjacent right-bank cylinders 2 and 1 consecutively.
Another way to extract more power from any engine is to increase the compression ratio. Ford says the Voodoo 5.2L motor enjoys a true 12:1 static compression ratio. The pistons travel in plasma transferred wire arc (PTWA) coated cylinder walls that essentially spray molten metal onto the aluminum cylinders. This saves weight over iron liners that traditionally are used in aluminum blocks. Next, the new four-valve-per cylinder heads are completely CNC-machined on both the intake and exhaust sides to improve flow potential beyond the capability of as-cast ports. Add two 1.51-inch hollow stem intakes and a pair of sodium-filled 1.28-inch exhaust valves opened to 0.551-inch lift for both sides and you have an aggressive combination that could have easily been a description of a full-competition road race engine from only a few years ago.
The innovations don’t stop there. Benefiting from computational fluid dynamics (CFD) computer assistance, the intake manifold received significant development work to increase breathing potential while not creating a peaky power curve. In fact, the Voodoo’s power band – defined as that rpm spread between peak torque and peak horsepower – is an amazing 2,750 rpm. A more traditional spread for late model production engines has been growing from a typical 1,700 rpm to wider bands like the 5.0L Coyote engine’s 2,250 rpm spread. Most engines that are tuned to increase peak horsepower at higher engine speeds tend to become “peaky” which means the power band narrows significantly. Even more impressive, because of the benefits from balanced exhaust pulse tuning, Ford says the Voodoo delivers 90 percent of peak torque between 3,450 and 7,000 rpm. This kind of linear power makes driving at higher power levels much more predictable.
We looked at some of the components that Ford displayed at the recent Rolex Monterey Motorsports Reunion at Laguna Seca near Monterey, California where the Shelby Mustang was the celebrated marque. Among the interesting internal changes included a forged piston that looked just like a Mahle right down to its unique Grafal coating. Lubrication systems are highly challenged with high engine speeds and Ford has addressed that issue with a composite wet sump oil pan with integrated windage control over its 10-quart capacity, adding a full 2 quarts to the capacity over the Coyote.
Starting with the reduced restriction of an open element air cleaner, airflow is essential if you expect to make power at 7,500 rpm. This requirement demanded a larger, 87mm throttle body but more importantly a properly designed intake manifold with runner lengths optimized both to make peak power (which calls for short runners) without sacrificing mid-range power (which calls for longer runners). Clearly this compromise has succeeded given the wide power band. Of course, variable cam timing also plays a part in this tuning dance.
All of these details eventually dovetail into a finished engine that once bolted in the car delivers an exhaust note that clearly was a big part of the reason for designing and building an engine that so dramatically departs from the norm. It’s interesting that at this time in the evolution of hybrid electric cars that are incredibly silent that Ford would choose to take the performance car in the complete, and we must say enjoyably so, opposite direction. Regardless of whether the scream this engine delivers was the driving force behind building the flat crank Voodoo engine, the end result is an exhaust note heard ‘round the world. Ford has just raised the performance bar not only with normally aspirated horsepower but with a little technology as well.
Listen To The Engine!