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Figure 1 VVT systems may vary in their details, b...

Figure 2 The Ford Triton 3 valve VCT configuratio...

Figure 3 The above and below left photos give you...

Variable Valve Timing Can Help Save V8s, Environment

I continue to marvel at the engineering tenacity of those who refuse to accept the “foregone conclusion” that the internal combustion engine will fall to the same fate of the dinosaur and that one day we will all be driving around in generic electric- or hydrogen-powered vehicles or some type of lawn mower-sized engine hybrid.

Not that I don’t support the environment and being responsible in our efforts to save the planet – I do. But the passion for the thunder of a throbbing, pavement-pounding V8 is, well, similar to that of the how your heart skips a beat when you think of your first love. What if you could still have the power, have great fuel mileage and still be environmentally responsible? That might be worth a Nobel Peace Prize in the eyes of many automotive enthusiasts.

There are technologies that have emerged in recent years that allow this to happen. I began last year with a similar hope for the future when I spoke of displacement on demand (or whichever name a particular manufacturer uses) technologies that will cut out cylinders based upon demand of power required, so a V8 may only use 4 cylinders while at cruising speed on the highway. But more recently, the use of variable valve timing (VVT) in numerous engines has brought an entirely new light to the situation. Case in point: the L99 GM engine in the ’10 Camaro with 400 hp /410 lb.ft. torque Gen IV 6.2L that implements both technologies.

Now, this technology isn’t new by any stretch of the imagination. It was toyed with as early as the ’60s by Fiat, and who has not heard of the i-VTEC engines by Honda more recently? The initial impetus to put VVT systems into production cars was the ever-increasing pressure to meet environmental goals and fuel efficiency standards while still maintaining reasonable performance. With today’s VVT systems, engines are so efficient at reducing emissions that the notorious separate EGR valve has become virtually extinct. VVT provides sufficient passive EGR charge dilution that considerable fuel economy, idle, and emissions benefits are achieved without the need to resort to clumsy add-on devices.

Although not originally its main intent, as applied to performance, VVT allows running a relatively radical cam that still maintains a stable idle and low-speed drive ability. As I pointed out above, VVT coupled with DOD should permit the survival of large-displacement V8 engines for the foreseeable future. Generally speaking, you want to advance a cam for more bottom end, higher vacuum, and better idle characteristics. Retarding a cam aids the top end. A typical production cam optimized for an advance/retard VVT system is usually ground with reduced overlap, with VVT retard dialed in as needed to maintain or enhance the top-end power.

Hydraulically actuated cam phasing is considered the preferred method for variably advancing or retarding a cam. An electronically controlled hydraulic valve or solenoid directs engine oil into a camshaft phaser assembly that replaces the timing chain’s camshaft gear. Inside the phaser cavity is a rotor that rotates within a stator as needed to advance or retard the cam. An additional advance/retard calibration table or map that relates cam lobe and crank position to engine speed is added to the electronic control unit (ECU). Figure 1 shows a typical VVT operation.

Ford’s terminology for this technology is variable camshaft timing (VCT). It’s available on SOHC modular engines with three-valve cylinder heads. In 2004, Ford became the first to offer VCT in a pickup truck, introducing the system on F-150 5.4L 3V Triton engines. Modular 4.6L SOHC 3V engines first appeared in the redesigned '05 Mustang. Since the SOHC V8 engine actually has two cams, one for each cylinder head, there are separate phasers, valves, and actuators that bolt to each head (Figure 2).

To supply the extra oil needed to actuate the two phasers, VCT engines use a new, thicker oil pump that supplies 30 percent more volume than even the higher-volume pump used on DOHC 4V engines. Losses from internal oil bleed-off are reduced with the use of new, rounder (less eccentric near the parting line) main bearings. Ford says mysterious cam phaser actuation problems can be minimized by using the new factory main bearings and sticking to factory production main and rod bearing clearances. Which is why I have brought you here in this article: main bearing clearances are .001˝ to .0015˝ and if you get outside of that the phasers will rattle like mad, making a horrendous racket.

The phasers can actually be taken apart and inspected (Figure 3) and, believe it or not, they are pretty straightforward as far as component inspection for wear. There is one area that you need to be aware of, however. There is an oil flow control valve and spring with a “plastic” component that will wear, especially if oil has not been maintained. If it goes bad then you will need to replace the phaser since there are no parts available that I have been able to find. With the three-valve engine being used in Ford trucks you can expect to see them showing up in your facility. Be certain to verify that they are viable and can be reused, or simply replace them (a step which will substantially increase your reman cost).

If you did not get the caution earlier, main bearing clearance is critical for oil volume, and phasers do require a bunch. When going undersize on the crankshaft you will most likely need to adjust your journal size for proper clearance, I strongly suggest you install bearings into the main bearing housing bore and determine what crank size you will need. If not, you may get that phone call that says “my engine sounds like a freight train rattling down the road.”

Roy Berndt has decades of machine shop experience. He is the EDS Data Acquisition Contractor for the Production Engine Remanufacturers Association (PERA), and Program Manager for PROFormance Powertrain Products, a PER in Springfield, MO. You can reach Roy at rberndt@enginebuildermag.com.