Not that I don’t supportthe 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 heartskips a beat when you think of your first love. What if you could stillhave the power, have great fuel mileage and still be environmentallyresponsible? That might be worth a Nobel Peace Prize in the eyes ofmany automotive enthusiasts.
There are technologies that have emerged in recent years thatallow this to happen. I began last year with a similar hope for thefuture when I spoke of displacement on demand (or whichever name aparticular manufacturer uses) technologies that will cut out cylindersbased upon demand of power required, so a V8 may only use 4 cylinderswhile at cruising speed on the highway. But more recently, the use ofvariable valve timing (VVT) in numerous engines has brought an entirelynew light to the situation. Case in point: the L99 GM engine in the ’10Camaro with 400 hp /410 lb.ft. torque Gen IV 6.2L that implements bothtechnologies.
Now, this technology isn’t new by any stretch of theimagination. It was toyed with as early as the ’60s by Fiat, and whohas not heard of the i-VTEC engines by Honda more recently? The initialimpetus to put VVT systems into production cars was the ever-increasingpressure to meet environmental goals and fuel efficiency standardswhile still maintaining reasonable performance. With today’s VVTsystems, engines are so efficient at reducing emissions that thenotorious separate EGR valve has become virtually extinct. VVT providessufficient passive EGR charge dilution that considerable fuel economy,idle, and emissions benefits are achieved without the need to resort toclumsy add-on devices.
Although not originally its main intent, as applied toperformance, VVT allows running a relatively radical cam that stillmaintains a stable idle and low-speed drive ability. As I pointed outabove, VVT coupled with DOD should permit the survival oflarge-displacement V8 engines for the foreseeable future. Generallyspeaking, you want to advance a cam for more bottom end, higher vacuum,and better idle characteristics. Retarding a cam aids the top end. Atypical production cam optimized for an advance/retard VVT system isusually ground with reduced overlap, with VVT retard dialed in asneeded to maintain or enhance the top-end power.
Hydraulically actuated cam phasing is considered the preferredmethod for variably advancing or retarding a cam. An electronicallycontrolled hydraulic valve or solenoid directs engine oil into acamshaft phaser assembly that replaces the timing chain’s camshaftgear. Inside the phaser cavity is a rotor that rotates within a statoras needed to advance or retard the cam. An additional advance/retardcalibration table or map that relates cam lobe and crank position toengine speed is added to the electronic control unit (ECU). Figure 1 shows a typical VVT operation.
Ford’s terminology for this technology is variable camshafttiming (VCT). It’s available on SOHC modular engines with three-valvecylinder heads. In 2004, Ford became the first to offer VCT in a pickuptruck, introducing the system on F-150 5.4L 3V Triton engines. Modular4.6L SOHC 3V engines first appeared in the redesigned ’05 Mustang.Since the SOHC V8 engine actually has two cams, one for each cylinderhead, there are separate phasers, valves, and actuators that bolt toeach head (Figure 2).
To supply the extra oil needed to actuate the two phasers, VCTengines use a new, thicker oil pump that supplies 30 percent morevolume than even the higher-volume pump used on DOHC 4V engines. Lossesfrom internal oil bleed-off are reduced with the use of new, rounder(less eccentric near the parting line) main bearings. Ford saysmysterious cam phaser actuation problems can be minimized by using thenew factory main bearings and sticking to factory production main androd bearing clearances. Which is why I have brought you here in thisarticle: main bearing clearances are .001? to .0015? and if you getoutside of that the phasers will rattle like mad, making a horrendousracket.
The phasers can actually be taken apart and inspected (Figure 3) and, believe it or not, they are pretty straightforward as far ascomponent inspection for wear. There is one area that you need to beaware of, however. There is an oil flow control valve and spring with a“plastic” component that will wear, especially if oil has not beenmaintained. If it goes bad then you will need to replace the phasersince there are no parts available that I have been able to find. Withthe three-valve engine being used in Ford trucks you can expect to seethem showing up in your facility. Be certain to verify that they areviable and can be reused, or simply replace them (a step which willsubstantially increase your reman cost).
If you did not get thecaution earlier, main bearing clearance is critical for oil volume, andphasers do require a bunch. When going undersize on the crankshaft youwill most likely need to adjust your journal size for proper clearance,I strongly suggest you install bearings into the main bearing housingbore and determine what crank size you will need. If not, you may getthat phone call that says “my engine sounds like a freight trainrattling 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 [email protected].
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