Depending on the application, a Coyote engine swap could possibly compromise one of the motor’s best selling points: its variable cam timing control or Ti-VCT.
Designed to widen the engine’s torque band and eventually improve the vehicle’s drivability, variable cam timing—also called variable valve timing in other engines—requires specific instructions from the engine’s ECU to operate properly. When a hot rodder planning a swap pulls a used Coyote engine from a salvage yard or purchases a new Coyote crate motor, he or she usually goes with an aftermarket ECU to keep the cost down or provide more tuning flexibility once the engine is installed.
While aftermarket ECUs are great at controlling the fuel and spark along with nitrous, boost and other engine features, they aren’t programmed to handle the dedicated phasers that adjust cam timing to achieve optimum power as the RPM and load change. Unless the user adapted a Ford ECU to the swapped Coyote, the most sensible solution was to lock the cam phasers so they wouldn’t default to an undesirable setting.
A new Coyote Ti-VCT control module from Holley EFI designed to work with the company’s popular HP and Dominator ECUs now solves this problem. Not only does it provide a solid baseline program that increases power and torque over a locked-cam setup, but it offers the option of custom programming if the user wants to play with the cam timing.
“Basically, this unit was developed for those who purchased a Coyote crate engine but don’t want to remove the cam covers,” sums up Robin Lawrence, director of EFI business development at Holley. “Most people don’t know how to degree a single cam, let alone four cams. We were really looking to offer a product that was plug and play.”
Pros and Cons of VCT
While there is always a debate over the pros and cons of variable cam timing in a racing engine, benefits in a street engine are rarely disputed.
“Most VCT isn’t good for over 8,000 rpm,” says Lawrence.
“On an all-out drag race car, I would not bother with VCT, and the reason being your operating range is very small, usually a couple thousand RPM,” says Holley engineer Ryan Witte. “In that small RPM range the cam movement becomes quite minimal to maintain peak power, a couple degrees of movement, and only relates to a couple percent in power at best. So, the benefit versus the risk on that doesn’t add up.
“On a road race motor, there is a lot more benefit to it. You have a wider RPM range with the lower RPM, low speed corners for example,” continues Witte. “But there is a limit to what camshafts we can control. Once you pass a certain point on the aggressiveness of the cam lobes, you cannot control the cam movement anymore. The valvespring pressure and the rate of the camshaft lobe will outrun what the oil pressure and the cam phaser can reasonably control.”
Just what is Ti-VCT? Short for Twin Independent Variable Cam Timing, Ti-VCT is Ford’s version of adjustable cam-timing or valve timing technology that is now very common throughout the automotive industry. Early variable cam timing was developed for single-cam applications and advanced or retarded the cam from its standard orientation to boost low-end torque or improve top-end performance—much like a knowledgeable tuner would do when setting up an engine for a specific application.
Remember, engine performance is affected not only by how long the valves stay open, but also when the valves open and close during their respective cycles. And we also know that engines have different airflow requirements at different speeds and loads. When the camshaft or the cam timing is fixed, then airflow through the engine is an efficiency compromise between high and low speeds, or there’s an emphasis on low- or top-end performance.
What is a Cam Phaser?
With variable valve timing on a single-cam engine, a phaser actuated by engine oil pressure advances or retards the cam position relative to the “straight-up” position. That means that the intake and exhaust valves advance and retard at the same time. The one notable exception to this limitation is the “cam-in-cam” technology used on the Dodge Viper V10. It was basically a hollow cam with a separate shaft inside. The outside tube controlled the exhaust valves and the inside shaft controlled the intake valves—which, in effect, established independent variable valve timing for that application.
With a 4-cam configuration like the Coyote, such intricate cam design is not necessary to achieve independent control of the camshafts. The Coyote’s Ti-VCT system is based around BorgWarner’s new CTA cam phasers.
Just what is a cam phaser? There are two basic components: an outer sprocket meshed with the timing chain, and an inner rotor that is bolted to the camshaft. As the inner rotor is moved and the rotation angle of the camshaft is changed, the valve timing changes.
The inner rotor is basically a set of lobes. Oil fills the space between the outer housing and the lobes. When there is no action, the rotor will spin at the same rate as the outer housing. But if pressurized oil is added to one side of the lobe and removed from the other side, the rotor will move and change the position of the camshaft.
Understanding Phaser Operation
The BorgWarner system developed for the Coyote is more advanced than conventional phasers that use just oil pressure to move the rotor. Called Cam Torque Actuated (CTA), this system captures torsional energy in the valvetrain to help actuate the cam movement along with the oil pressure. This system requires less engine oil to operate than conventional variable valve timing systems. These advanced features help the phaser respond quicker off idle and don’t require special high-pressure oil pumps that drag power down from the engine.
“Solenoids still operate the phasers, and the Holley module controls the solenoids,” stresses Witte, noting that there is a difference in the amount of control flexibility, depending on which engine is used. “It’s 50 degrees on Gen I Coyote engines and 70 degrees for the intake on Gen II.”
Independent control of each phaser allows engineers to manipulate the engine’s breathing for the most efficiency or power. Variable valve timing doesn’t change the duration or lift of the camshafts, it just changes the timing when the valves open and close. Much of the strategy involves adjusting the overlap period when both the intake and exhaust valve are open at the same time at the end of the exhaust stroke. In fact, Ti-VCT can eliminate overlap, if needed, to improve fuel economy or reduce emissions.
“Overlap is what you really want to tune. Because you have a dual overhead cam motor, you can play with the exhaust lobe and intake lobe independently of each other, which gives you a lot more freedom on how to affect the torque curve of the motor,” says Witte.
Improved Drivability is the Key
The beauty of the Holley Coyote Ti-VCT control module (PN 554-145) is that the user doesn’t have to worry about programming in a cam timing strategy.
“The unit plugs into the Dominator or HP ECU and into Coyote sub-harness that connects to the phasers and cam sensors,” explains Lawrence.
Because of changes between Gen 1 (2011-2014) and Gen 2 (2015-present) Coyote engines, the Holley module must be set up so that the correct pre-programmed table will be used at start-up. There is a bank of dip switches on the back of the controller that the user adjusts according to the instructions. A laptop is then connected to the ECU.
“You would load a base tune that we supply,” adds Witte. “It’s in the V5 software for either the early or late motors. In the V4 software, it’s the early motor, only. For a stock motor, it would be–open the laptop, select the tune, either ’11 to ’14 or ’15 to ’17, load it, do your TPS auto set, start it up and drive it.”
Holley set up the base maps with certain compromises for the best power and drivability in addition to reliability. And the base maps were developed using the factory Coyote cams.
“A stock engine doesn’t allow you to do anything that would hurt the motor. It may not make as much power if the cams are moved way too far in one direction, but there’s no mechanical interference,” says Witte. “The valves will never hit each other, or the pistons. In that regard, it’s just tuning fuel and timing for the chosen cam position.”
Holley has tested its base map with aftermarket cams for the Coyote, specifically the NSR cams from Comp Cams that don’t require stiffer valvesprings.
“We have found we can control those just fine,” says Witte.
Default Positions Aren’t Performance Minded
The Holley module can deliver up to 50 degrees timing variance on both the intake and exhaust cams for the Gen 1 engines and 70 degrees on the intake side for the Gen 2 engines. Should the user want to change cams and develop a custom map for the cams, the Holley module offers that option.
“If you were using one of the no-spring-required (NSR) cams, you would flip the switch on the controller and use the tables in the Holley EFI, and you could remap it for optimum performance,” says Witte. “With an aftermarket cam, there is likely going to be some benefit to remapping the cam positions.”
The primary motivation, however, for developing the Holley Ti-VCT control module was serving builders who swap a Coyote engine into a hot rod or musclecar and don’t want to lock the cams. Such a stance also begs the question: What if I just leave the phasers and cams alone—don’t hook up any wires or change anything?
“The Ti-VCT on the Gen I defaults to a retarded position, so they don’t run very well,” says Lawrence. “On the Gen II Coyote, if you unplug the VCT it will default to a central position, so they run pretty good. I think our numbers are 40 horsepower down in default, but the engine will run.”
The Holley control module also features diagnostic LEDs to inform the user if a cam or crank sensor fails. The module does require the installation of an external MAP sensor.