5.0 Mustang & Super Fords
2011 Ford Mustang GT 5.0 Coyote Engine
For The First Time Ever, The Mustang Gets Its Own V-8-And We Get The Inside Story On Its Birth
Some may wonder why the Coyote is not debuting with EcoBoost, Ford's combination of direct fuel injection and turbos. It's a fair question, but after driving EcoBoost in everything Ford puts it in, we're not missing it on the Coyote.
EcoBoost is efficient, torquey, somewhat revvable, and expensive. For a performance car, its personality is a hint cool, without an exhaust snarl or light-speed snappiness. In fact, after 25 years of driving performance cars, we're convinced there is nothing better than a crisp 400-500hp, naturally aspirated small-block when it comes to driving fun. The Coyote comes awfully close to perfection on paper, so we're really looking forward to driving it.
For the Coyote team, Mike Harrison expresses the inevitable concern. "I'm personally worried that when it launches people will think, 'Oh, doesn't it have DI on it? You know, it's not relevant.' I'm a bit worried about that, but I hope the metrics will speak for themselves, because we're delivering DI-like performance. We're trying to leave the impression it is fully competitive without it."
A big reason Mike isn't too concerned is the Coyote has garnered much of EcoBoost's advantages without the cost.
As a Coyote team engineer put it, "On a naturally-aspirated engine, the biggest benefit of DI is charge cooling-and it's a volumetric efficiency benefit and not a tolerance benefit. We squirt the injectors while the [intake] valve is open, and it's open a long time, which we haven't done before. It seems simple and gets you half the benefit of DI-for no costs at all."
The only apparent downside is cylinder-wall washing at low engine speeds, so the injector is limited to closed-valve periods at low rpm. Also, the camshafts change valve timing, so that's something else to synchronize with the injector in the engine management calibration.
Twin independent Variable Cam Timing
Trick as it is, TiVCT is not new. It's been used in other Ford engines, mainly in Europe, since 2004. Its job is to vary the timing of the intake and exhaust valve events, and to do so independently of each other. To accomplish this, separate intake and exhaust camshafts are required, so the technology wasn't available to the Three-Valve 4.6 V-8. Furthermore, the Coyote uses cam torque actuation with its TiVCT, which we'll cover in a minute.
Advantages to TiVCT are immense, and the Coyote would not come close to its impressively wide powerband, high peak power, and fuel economy without it. With TiVCT, the Coyote torque and horsepower peaks are separated by 2,250 rpm, whereas the Three-Valve 4.6 peaks are 1,750 rpm apart using variable cam timing on a single cam. The 4.6 Two-Valve peaks are but 1,200 rpm apart with fixed cam timing, and the venerable pushrod 5.0 H.O. peaks are separated by a mere 1,000 rpm.
Camshaft movement in traditional TiVCT systems is accomplished by porting pressurized oil into the cam phasers attached to the drive end of each camshaft. These have two each advance and retard chambers to physically move the cams. Pressurized oil is routed into the chambers by a shuttle valve and solenoid actuator under computer control.
The Coyote's TiVCT benefits from cam torque actuation. Instead of high-pressure oil energizing the cam phasers, CTA uses the valvespring energy torquing through the camshafts. At certain periods of cam rotation, valvespring pressure tries to advance the cams, and retard them at other points. This snappy back and forth energy is traditionally dissipated uselessly into the timing chains, but with CTA it's used to power the cam phasers. Engine oil is still used to fill the cam phaser chambers and thus hold the new cam position, but not physically advance or retard the cam-that work is done strictly by cam torque from the valvesprings. As such, there is no hardware in CTA. It is only a strategy.
In fact, in exchange for some crafty thinking and hard-won computer software, there are less hardware and cylinder-head-design headaches with CTA. The control mechanism for shuttling oil in and out of the phasers is a simple solenoid because the three-way shuttle valve is not required. High-pressure oil is also not needed, so the engine's oil pump can be downsized and horsepower saved. Nor are dedicated oil passages to the phasers required. Instead, the Coyote's TiVCT with CTA system siphons off bleed oil from the nearest cam journal.
Control of the system requires a camshaft position sensor on each camshaft, plus the crankshaft position sensor. While cam timing is locked into a base mode during some engine modes, namely start and WOT, the rest of the time the cam timing can be all over the map. The engine management computer runs numerous algorithms to determine where to position each cam independently of the others.
Cam timing can be varied up to 50 crankshaft degrees, and the change made in just 0.2 second. The engineers have a field day with TiVCT, noting they can dial in more valve overlap than the raciest conventional cam or run minimal go-to-church valve timing. Aside from the obvious power benefits, TiVCT definitely increases fuel economy during light throttle and cruise modes. Other uses of TiVCT are to increase valve overlap at certain points to increase incoming charge dilution with exhaust gasses. This is passive EGR, which eliminates the need for an EGR system on the Coyote.
If the highly unlikely event the timing chains or VCT units fail, the Coyote is a free-wheeling engine, so the pistons and valves won't crash.