

How Engineers Pushed The 2020 Shelby GT500 Powertrain To Deliver Supercar Level 0-100-0 Performance

HOT ROD logo HOT ROD 8/14/2019 Steve Turner,Courtesy of Ford

a close up of a motorcycle engine: 001-2020-Shelby-GT500-Powertrain
The Predator snarls as the Michelin Pilot Sport Cup 2s dig into the surface. The driver is pushed back into the Recaro seats as the Tremec TR-9070 seven-speed dual-clutch transmission upshifts each gear in 80 milliseconds. In the blink of an eye the 2020 Shelby GT500 is traveling at 100 mph. Suddenly the driver thrusts a foot on the brakes. The massive, six-piston Brembo calipers lock down 16.5-inch rotors, and the g-forces mimic those of Ford GT decelerating at Le Mans. In 10.6 seconds, it is back to a standstill.

If this had taken place on the flight deck of an aircraft carrier, there would still be room to spare, but no matter the venue, the performance is elite, especially for a Mustang.

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"The range of brute-force drag acceleration, seamless road shifts and amazingly smooth shifts on the track further highlights how the soul of the Shelby GT500 is elevated in our most advanced Mustang ever," said Ed Krenz, Ford Performance chief program engineer. "Effortlessly handling the 760 horsepower is our segment-first Tremec dual-clutch transmission, with an advanced control system that enhances GT500's five drive modes to deliver a driving experience once reserved only for exotic supercars."

Regular readers know we dug deep to bring you plenty of detail on the forthcoming halo Mustang, particularly regarding its formidable supercharged 5.2-liter engine. Known appropriately as the Predator, this engine belts out 760 horsepower and 625 lb-ft of torque. Using its cousin the Voodoo 5.2-liter as a jumping-off point, engineers beefed up the block and heads; switched to a cross-plane crankshaft; and topped it with an intercooler Eaton 2.65-liter TVS supercharger.

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That is painting with a broad brush, but you get the idea. The Predator is a whole new animal. We have covered much of the nuance in our previous stories, but on a sunny day in Michigan we had a chance to chat one-on-one with the engineers spearheading the creation of this car and we learned a few more things about the engine and the rest of the powertrain that delivers that supercar-challenging performance and sustains during extended track outings.

Among the upgrades needed for a car performing at this level was a stronger engine block. While the extant 5.2-liter block was plenty strong for high-revving, naturally aspirated action, the move to boost and a cross-plane crankshaft meant the Predator 5.2 block needed more meat in some places, and a different approach to transferring cylinder pressure from bay to bay via strategically placed ports to control windage. Where those ports were needed in this engine changed based on the traditional crank and the increased cylinder pressures.

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"So we actually have this set up where we, they have to come in from both ends and different times and put holes in different places because what works in one bay doesn't work in the next bay because of the firing order and the loads and the bulkheads," Pat said. "It's different from each bay. So a lot of analytic work was done both with the crankcase breathing and with the structure and the CAE and parts and quite a bit different."

That shows just how far engineers went to ensure this engine would perform, and that is true of the cylinder heads as well. They bolstered the material on the water jackets to strengthen them and treated the castings to a CNC port job to extract another 2-3 percent of flow, which will also benefit the Shelby GT350, as the improvements were rolled back into that engine as well.

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One thing that is common between the two 5.2-liter variants is the exhaust manifold design. You might assume the cross-plane crank would want a completely different exhaust design, but engineers discovered that the existing short-tube design worked just fine for this application as well.

"So in fact, what you'll find is we did a lot of testing with this manifold and some other manifolds. We are lot of analytic 1D modeling, and we found out that this is a pretty good manifold for cross-plane as well. Really good," Pat Morgan, Ford Performance powertrain manager, said. "And of course you can look under the hood and see it is fairly tightly packaged, especially on the left side where you got the steering shaft. We've got to contend with that. We've got to contend with the catalyst. There's pretty much one place to put a catalyst in this car, where it is. It actually works really well. It was the best for performance, right? So people will look at it and think that we compromised so it'd be common. Actually that's not true. We picked the best for power.

a close up of a motorcycle: 006-2020-Shelby-GT500-Powertrain.jpg© Courtesy of Ford 006-2020-Shelby-GT500-Powertrain.jpg

Obviously power is plentiful on this car, but putting it to the pavement was the real mission, and from the jump a dual-clutch was the plan. Engineers never even considered a manual transmission, as maximizing the potential of the vehicle was the mission. As we know they turned to the Tremec TR-9070 DCT dual-clutch transmission to get the job done.

"In many ways, this is like having two transmissions in one," Pat said. "On one hand, it enables performance at the outer reaches of straight-line quickness with minimal torque interruption, yet provides an incredible amount of finesse and control in track environments for maximum stability and predictability at the limits of lateral acceleration."

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Using five friction plates in its odd gear pack and another six friction plates in the even gear pack, the TR-9070 DCT feeds fluid to the clutches only as temperatures rise, while its seven non-sequential forward gears use triple-cone syncros matched to the engine torque curve to achieve smooth shifts. Actuating those shifts is an electrohydraulic shift mechanism using energy-efficient low-leak solenoids. All told it can shift in as little as 80 milliseconds, but do it so smoothly that it can actually change gears mid-corner without upsetting the car.

Interestingly, such an emphasis was put on the alacrity of the shifts, engineers opted to give the steering wheel-mounted paddle shifters a direct line of communication to the transmission control module.

"There's a wiring harness inside the oil pan and I think its 14 solenoids that control the mechatronics and the shifting. In order to get it to shift in 80 milliseconds, we actually hardwire the paddle shifts. It's a direct wire," Pat said. "We have this typical CAN that all cars have these days for all the other communications, port control and all that stuff. But for the paddle, when the driver commands a paddle, it goes straight to the TCM."

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The result is a system that can implement a shift in as little as 130 milliseconds, and complete the shift much quicker than that. Relying on engine rpm, transmission rpm, driver input, g-forces, clutch position, and shift-fork position data, the system optimizes the shift for what's needed at that moment, and based on feedback from test and professional drivers, the shifting logic is right where it need to be for the given situation.

"Contrary to popular belief, fast shifts do not always equate to better road performance," Pat added. "In every driving situation, we emulated what professional drivers do, whether it's a smooth, precise heel-and-toe shift of a professional track driver or a much more forceful powershift like drag racers. We've designed the perfect shift every time."

Another enabler to sharpening the DCT shifts was actually the move to a one-piece carbon fiber driveshaft, but not for the reason you might assume.

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"The carbon fiber driveshaft, you would think it's entirely about light weighting and to some degree that's true. But with the metal couplings at either end, it's not a massive weight savings," Ed explained. "It really gets to minimizing lash and rotational inertia. And, you know, getting, hitting the sweet spot on the tube diameter and thickness was where the engineering was really involved. We looked at different wall thicknesses, different diameters (which are obviously limited to maximum diameter), while really honing in on the, the optimized tube diameter."

Beyond the hardware, adjusting between the five available drive modes obviously also alters the transmission's shifting characteristics to meet that mission, while also tweaking the throttle response, stability control, braking, and steering feel.

"Every aspect of the Shelby GT500 driving experience changes with the mode — be that the throttle responsiveness and snap of the shifts you feel in the seat of your pants, or the 'pop and burble' of the exhaust in performance modes. It's a full multisensory visceral experience," Pat added.

Of course, using a DCT in a car that can perform at this level meant doing a lot of development to ensure the transmission stays properly lubricated under the high g-forces of corners and launches.

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"I can tell you on the engine side, we've got some really good simulation trends, so it's pretty close, and it even picks up all the dynamics from bay to bay with the breathing and everything. So that was really, really valuable," Pat said. "And then it was a little bit later in the program that we shared some of those techniques with Tremec and developed some of their own techniques. And, and actually that's how we ended up finding the solution was analytically... '"

Much like they did with the trap-door oil control on the engine oil pan, engineers used simulations and plenty of real-world testing to ensure the lube stays where the transmission needs it, as starving a DCT of lubrication can be catastrophic.

"And that was, that was a bit of new learning for us because in the past when you run a manual transmission, you don't really care where the oil goes, because of the splash. And if it does have a problem, like our GT350 has, it's just for cooling," Pat explained. "So now we have to depend on pressurized lubrication system to keep your clutches cool and the clutch system on this thing is pretty cool because it senses when it's getting a high heat load from a lot of use and then increases oil flow to the clutches to keep them at the right temperature; it's a pretty neat piece with a very intelligent lubrication system."

Keeping things cool when the GT500 is running at full tilt on the race track was clearly a challenge, and one that engineers took on with gusto. They told us that the car could run flat out until the fuel tank ran dry without de-rating, which means it won't heat-soak and rein in the engine's output.

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"In years gone by there were different products, ours and others, that they're good for the dragstrip, and they're good for a quick run, but you get out on a warm day and you heat soak it and it starts de-rating. So we put a lot of effort into this to be sure that didn't happen. That's a big deal to us. What I'm really happy with is that we've got some very capable drivers and we also pulled in our pro drivers from racing to drive the car and evaluated and they love it. They can exercise it tank after tank after tank of fuel — all day long," Pat said. "We run the equivalent of 24-hour endurance to be sure the whole car's validated for that. But then in addition to that, we've had so many cars on the track and like I said, over 5,500 laps and hundreds of hours, those on the tracks. That's not counting proving-ground tests"

If testing on multiple race tracks on both sides of the country and in-house tracks in between seems like a lot effort to expend on the cooling system, remember that generating 760 supercharged horsepower creates a lot of heat, and engineers did not want the power they created to fall by the wayside on a hot day. This car had to perform at a high level in the harshest conditions.

"The biggest engineering job at the mid-point in the program was getting the cooling system correct. Our goal was to analytically design the cooling system such that when we built the first prototype, we had no issues with a de-rate," Ed said. "On prior programs we were engineering the cooling system until we ran out of time. This was a stop-the-program for-several-months type of deal to redefine all the coolers, get all the analytical sign-off data, and prove track capability analytically. The front end is all about the cooling. So we said that it's 50-percent bigger than the GT350. Strictly that's true, but from our front-end opening airflow perspective, it's actually 100 percent greater than the GT350."

And, it's likely safe to say that the GT500 is far greater than its high-revving cousin as well, but that remains a story for another day. However, it is safe to say that Ford Performance engineers did everything they could to ensure this car will build on the Shelby GT500 legacy in fine fashion.


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