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The Advantages of Using a VVT Cam in a Gen IV and Gen V Engine

VVT Is Your Friend: Variable Valve Timing is an idea whose time has arrived

Jeff Smith Aug 22, 2018
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Decades ago (OK, half a century or more), there was a product advertised in many of the performance magazines called the Varicam. The idea was a set of springs attached to a centrifugal device that would retard the cam with rpm. The idea was innovative and right on target, but the execution left much to be desired, and eventually it disappeared.

Now let’s fast forward to the 21st century. We’re not piloting flying cars, but we do have VVT (variable valve timing). Starting with the Gen IV LS engines, GM engineers figured out a way to direct engine oil pressure to swing the camshaft through an enormous range of movement. The early Gen IV engines could move the cam over a maximum potential swing of 62 crankshaft degrees. This is an idea whose time has come, but like most innovations, it has been slow to be accepted by the performance industry.

We thought it might be a good idea to do a quick drive-by, highlighting the advantages of VVT in the Gen IV and V engines. What we will reveal is how well it works and why it’s best to take advantage of the power opportunities offered by a VVT-equipped engine rather than just perform a VVT-delete before you know what you’re dumping.

Before we get into exactly how VVT works, we thought we should explain why VVT is such a good idea for a number of excellent reasons. We sought out Jason Haines, who until recently was a development engineer at Lingenfelter Performance Engineering (LPE) and has now started his own consulting firm—Product and Service Solutions. Jason has a wealth of experience with GM’s VVT and offered some interesting points.

Variable valve timing offers some wonderful opportunities for the engine designer and builder. With a single camshaft/pushrod engine, moving the camshaft simultaneously alters all four of the valve events: intake opening (IO), intake closing (IC), exhaust opening (EO), and exhaust closing (EC). While all four are essential, the most important valve event of the four is IC. This determines cylinder filling throughout the engine’s rpm band.

If all we had to do was make power within a very narrow 1,200-rpm band—as with a five-speed manual trans drag race combination or a cabin cruiser boat engine that operates 98 percent of the time at a set cruising rpm—then moving the camshaft around is of limited benefit. But street engines are expected to deliver excellent power and throttle manners between idle and 7,000 rpm. This is where VVT really shines.

VVT is all about advancing or retarding the camshaft. To make this simple, we can discuss this using the intake centerline as our reference point. Let’s use a mild street hydraulic roller cam as an example. We will discuss this in relation to the cam’s intake closing point as that’s what affects both power and, to a certain extent, street manners.

Advancing or retarding the camshaft means that we will be moving the intake closing point in relation to the piston. Advancing the centerline will shift all the valve events to open and close earlier. Specifically, advancing the cam four degrees means the intake closing point will now occur four degrees earlier than its original position. If we retarded the cam the same four degrees from “straight up,” this would place intake closing four degrees after its original position.

We’ve created a small chart that lists the effects of advancing and retarding the camshaft that is worth studying. In a general sense, advancing the cam tends to improve low-speed torque while retarding the cam will improve high-speed power. For street engines with a fixed timing position, the engine builder is forced to choose a compromise position mostly based on how the engine would be driven. If the engine was predominantly street driven, this generally meant the cam would be advanced.

To this point, most street cams are actually machined with a minor amount of advance built into the cam. You can quickly tell just by comparing the lobe separation angle (LSA) to the cam’s intake centerline as listed on the cam timing card. If the intake centerline is 108 but the cam has an LSA of 110 degrees, you instantly know the cam has been machined with two degrees of built-in advance.

Not only does moving the camshaft affect where the engine makes power, but it also affects other related issues, such as piston-to-valve clearance. With increased lift and duration, this moves the valves closer to the piston at certain points. This is why several companies build VVT limiters, which reduce the VVT’s range of operation to prevent the valves from smacking the pistons while still allowing a relatively wide range of advance and retard.

We recently tested a Gen V naturally aspirated LT1 on the dyno at Westech Performance in Mira Loma, California. This was our first foray into both gasoline direct injection (DI) and VVT. The advantages of these two developments quickly became apparent with the first dyno pull. We started the test with a set of headers and an electric water pump as the only upgrades.

After some very minor tuning to the wide-open throttle (WOT) air/fuel ratio (from the factory these engines run very rich at WOT) and adding a couple of degrees of timing, this engine made spectacular power. This was a 6.2L LT1 with 11.5:1 static compression and direct injection and the VVT. If you look at the power curve graph, notice that this engine makes 480 lb-ft of torque at 3,000 rpm and then carries that power all the way out to 518 horsepower at 5,800 rpm.

To put this achievement into perspective, a base 454 H.O. Rat motor that is 78 cubic inches larger makes about the same torque at 3,000, but only offers 438 peak hp. Part of the reason for this greater power is certainly due to the LT1’s higher static compression and the direct injection, but an equally large part can be attributed to VVT.

Here’s how GM does it. All VVT control is actuated using hydraulic oil pressure. This starts with the oil pump, which is different than previous LS pumps. This pump is a sliding vane design. If you’ve ever seen inside an automatic transmission front pump, they are of a similar design. The pump must deliver greater volume as well as higher pressure in order to supply the demand requirements of the VVT system. The Gen IV engines used a higher-volume and pressure pump, but it still remained a gerotor design.

Oil pressure is applied to a valve in the front of the camshaft that also doubles as the cam gear retention bolt. Oil is supplied through a galley in the front portion of the camshaft supplied by oil from a groove in the second cam journal from the front. All cam movement is controlled with an electronic solenoid mounted on the cam timing cover that sends commands to the cam gear bolt/valve. The valve is machined with multiple holes that direct oil pressure to either advance or retard the camshaft.

Inside the cam timing gear is a series of slots that allows movement between the actual chain-driven portion of the gear and where it connects to the camshaft. In the early engines, this allowed as much as 31 degrees of movement. In both versions of VVT, this is far more potential movement than what is actually used. Haines says that most LS VVT engines limit the range of movement to between 20 and 25 crankshaft degrees of movement. Even then, this greater movement is limited to light throttle applications where the cam is retarded to reduce manifold vacuum. By minimizing intake manifold vacuum, less negative work is done, which offers a slight benefit to fuel mileage.

The “parked” or standard position for VVT engines is full advance. So when viewing the VVT table on a HP Tuners or EFILive edit screen, you will see a chart with mostly double–digit numbers. These numbers represent the amount of retard tuned into the system.

This amount of authority also presents a problem. The factory system is carefully designed in conjunction with the stock cam to prevent piston-to-valve (P-V) contact. This isn’t difficult with the short duration and conservative lift numbers of the factory camshafts. But in a performance situation, we’ve all seen that even slight increases in cam duration can have a very positive effect on peak power.

When a bigger cam with more lift is added to a stock VVT engine, many think that this requires that the VVT system be deleted, which isn’t true. There are kits available from companies like Brian Tooley Racing and others that offer this feature. But there are also limiter kits available that will allow the addition of a slightly longer duration camshaft while still retaining VVT function, although with less overall movement.

For example, LPE offers a GT32 cam for naturally aspirated LT1 and L86 engines with specs of 225/241-degrees of duration at 0.050 with 0.643/0.657-inches of valve lift on the intake and exhaust, respectively, and can still be used with the factory VVT. This will, however, require a cam limiter system, which is also available from LPE.

This is where taking advantage of VVT for a performance engine comes into play. Adding duration to increase power tends to soften the amount of torque the engine makes at lower engine speeds. But with VVT, it’s possible to advance the cam slightly at lower engine speed, which improves the low-speed torque, throttle response, and even fuel mileage. Then at higher engine speeds, the cam can be retarded several degrees to offer horsepower advantages. These power advantages can easily exceed 10-15 lb-ft of torque at low speeds and 10-15 horsepower at peak engine speeds. Why leave that power on the table?

This really is the best of both worlds where a savvy cam selection for a street engine can offer power improvements across the entire rpm band from idle to peak horsepower. This will become the smart money move for future performance engines, not just in factory cars but also in engine swaps, especially as the Gen V engines like the LT1 and L86 become available at a lower cost. VVT is an idea whose time has come and the smart builders are already taking advantage of the technology.

001 Lt1 Crate Engine 2/12

All Gen V engines, even this Chevrolet Performance LT1 crate engine are built with VVT. Production LT1s also come with Active Fuel Management (AFM), but Chevrolet Performance crate engines disable this feature, although the components are still in place.

002 Variable Valve Timing Cam 3/12

This is a VVT camshaft from an LT1. The large gear on the front of the cam is the actuator that controls the camshaft through its 31 degrees of potential movement. Also note the groove cut into the second journal. This groove is what directs oil from the main galley forward to the actuator.

003 Lt1 Engine Cutaway 4/12

This David Kimble cutaway drawing of the Gen V LT1 reveals the groove in the camshaft Number Two journal and also reveals an inside look at the cam phaser in front of the actual cam gear. Note the amount of room available for the phaser to move.

004 Vvt Sliding Vane Pump 5/12

VVT requires a much larger volume of oil and higher pressure to ensure accurate timing control. This is accomplished with a variable volume, sliding vane pump similar in design to automatic transmission pumps. The center of the pump can be moved to alter the output volume.

005 Cam Phaser Actuator Solenoid 6/12

If you are junkyard searching for a Gen IV engine with VVT, a quick identification is to look for the cam phaser actuator solenoid, which is the large hub with electrical connectors located on the front timing cover. Early Gen IV engines like the LS2, LS3, LS7, LSA, and LS9 did not employ VVT. Conversely, all Gen V engines come with VVT and AFM.

006 Variable Valve Timing Cam Bolt 7/12

This is the cam bolt that also serves as the valve that directs oil in various directions to move the phaser to either advance or retard the camshaft.

007 Lt1 Engine Dyno 8/12

We dyno-tested a relatively stock Gen V LT1 engine upgraded only with an electric water pump and 1 7/8-inch JBA headers with mufflers and made an amazing 518 hp and 522 lb-ft of torque on an otherwise stock engine. The best part was the low-speed torque that can at least be partially attributed to VVT.

008 Lt1 Dyno Graph 9/12

This is the power curve we generated on that near-stock Gen V LT1. What impressed us was the 480 lb-ft of torque at 3,000 rpm and the average of 502 lb-ft of torque between 3,000 and 5,000 rpm. Those are big-block numbers generated by an all-aluminum small-block. At least a portion of this torque can be credited to VVT.

Gen V LT1 w/ VVT
RPM Torque HP
3,000 480 274
3,100 484 286
3,200 481 293
3,300 479 301
3,400 479 310
3,500 481 321
3,600 484 332
3,700 490 345
3,800 497 359
3,900 504 374
4,000 509 388
4,100 513 400
4,200 515 412
4,300 516 422
4,400 518 434
4,500 519 445
4,600 521 457
4,700 522 467
4,800 521 476
4,900 518 483
5,000 515 490
5,100 512 497
5,200 508 503
5,300 502 507
5,400 496 510
5,500 490 513
5,600 484 516
5,700 477 517
5,800 469 518
5,900 460 517
6,000 453 517
Peak 522 518
Avg. 491.3 433.1

009 Lubrication Circuit Cutaway 10/12

This David Kimble cutaway reveals the lubrication circuit that starts with the sliding vane oil pump over the crankshaft nose and winds its way around the engine.

010 Hp Tuners Graph 11/12

This is the HP Tuners page for VVT control. Maximum load would be at the bottom of the chart with highest rpm on the far right. Note that the biggest numbers occur at light throttle (shaded yellow). This is because GM “parks” the cam at full advance, so the numbers refer to the number of degrees of retard implemented. GM retards the cam at light throttle to reduce intake manifold vacuum.

011 L86 Engine 12/12

A sleeper engine worthy of attention is this L86 VVT- and AFM-equipped truck engine. Remove the front accessory drive, intake manifold, and oil pan and this is the exact same engine as the wet-sump Corvette LT1 and Camaro version LT1. The hot ticket is to delete the AFM but retain VVT and add a mild cam and the engine could easily make 550 hp and run much like a stocker.

VVT Engines
The VVT modification in the Gen IV V-8 engine began in 2007 and continues to the present with the Gen V. We’ve only listed the 6.0L and 6.2L engines in this list but there are many more VVT engines in the 4.8L and 5.3L displacements.
Gen IV 6.0L
RPO Compression HP Flex Fuel
L76 9.6:1 367 No
L96* 9.6:1 360 No
LY6 9.6:1 364 No
* GM crate engine PN 12677741
Gen IV 6.2L
RPO Compression HP Flex Fuel
L92 10.5:1 403 No
L94 10.4:1 403 Yes
L99* 10.7:1 400 No
L9H 10.5:1 403 Yes
* GM Crate engine PN 19244102
Gen V 6.2L
RPO Compression HP Flex Fuel
LT1* 11.5:1 460 No
LT4** 10:01 640 No
L86 11.5:1 420 No
*GM crate engine PN 19328728
**GM crate engine PN 19332621

Advance vs. Retard
Advanced
Early intake closing creates more cylinder pressure at lower engine speeds
Earlier exhaust opening reduces pumping losses to improve fuel mileage
Builds more cylinder pressure at lower engine speeds for better torque
Decreases intake piston-to-valve (P-V) clearance
Increases exhaust P-V clearance
Retarded
Later intake closing point delays maximum cylinder pressure to higher engine rpm
Delayed exhaust opening allows longer cylinder pressure push on the piston
Builds more high-rpm power
Increases intake P-V
Decreases exhaust P-V
Lobe Separation Angle (LSA) does not change with advance or retard

Photos: Jeff Smith, General Motors, GM Media Archive

Sources

Westech Performance Group
Mira Loma, CA
951-685-4767
www.westechperformance.com
Lingenfelter Performance Engineering
Decatur, IN
260-724-2552
www.lingenfelter.com
Brian Tooley Racing
888-959-8335
www.briantooleyracing.com
Chevrolet Performance
chevrolet.com/performance
Product & Service Solutions
www.proservsolutions.com

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