eallanboggs

iTrader: (1)

Does anyone know how VVT works? The exploded picture in the brochure shows a device mounted on the front of the cam timing sprocket I've never seen before. I'm sure this is how they do it, but how do they activate it? I'm wondering if an aftermarket cam or double row Rollmaster will work on this engine? I'm sure the old style lifters won't work on it at least not on the cylinders that are shut off during lean cruise mode. Also, does anyone know how they activate and deactivate these special lifters to get the 4 cylinders to shut off. They somehow control the oil flow to these lifters to disable 4 cylinders at highway speeds?

nice_n_lo_silverado

iTrader: (1)

It moves the degrees of the cam positive or negative. kind of like adding and removing timing for the spark.

Grumpy5.3

iTrader: (14)

do you mean Displacement on demand???? it is totally diffrent from vvt

Bill Reid

iTrader: (14)

Here is the info lifted from another site after Googling "L92 Cam Phaser"... for VVT and DOD

Bill

"Displacement On Demand

Some 5.3L and 6.0L engines are equipped with GM’s fuel-saving Displacement On Demand technology, which can temporarily shut down the combustion process of half the engine’s cylinders under certain driving conditions to save fuel. GM was the first manufacturer to offer this fuel-saving technology on trucks. On the new full-size SUVs, it works with other attributes, such as improved vehicle aerodynamics, to maintain GM’s fuel economy leadership in the segment.

A sophisticated engine controller determines when to deactivate cylinders, allowing the engine to maintain vehicle speed in lighter-load conditions such as highway cruising. The process is seamless and virtually imperceptible. When the cylinders are deactivated the engine effectively operates as a V-4, with alternate cylinders on each cylinder bank disabled. The engine returns to V-8 mode the instant the controller determines the vehicle speed or load requires additional power. The key to DOD’s efficiency and virtually imperceptible operation is a set of special two-stage hydraulic valve lifters, which allows the lifters of deactivated cylinders to operate without actuating the valves.

The valve lifters have inner and outer bodies, which normally operate as a single unit. When the engine controller determines cylinder deactivation conditions are optimal, the outer body moves independently of the inner body on the disabled cylinders’ lifters. The outer body moves in conjunction with camshaft actuation, but the inner body does not move, holding the pushrod in place. This prevents the pushrod from actuating the valve, thereby halting the combustion process. Solenoids in the engine lifter valley operate to deliver high-pressure oil to the switching lifters, activating a release pin to separate the inner and outer bodies. Oil circulation and pressure do not vary, regardless of the engine’s operational mode. Lifter design and pushrod length are the same for every cylinder, but camshaft lobe profiles differ for cylinders designated to be deactivated.

The engine’s electronic throttle control (ETC) also is used to increase manifold pressure in V-4 mode so that the engine can maintain a V-8 torque load.

Variable valve timing

Variable valve timing (VVT) is a standard feature on 6.0L and 6.2L engines; it helps optimize camshaft timing to improve low-rpm torque and high-rpm horsepower. The introduction of variable valve timing through the unique dual-equal cam phaser is the industry’s first application of VVT on a mass-produced V-8 cam-in-block engine. The unique dual-equal phaser adjusts the camshaft timing at the same rate for both the intake and exhaust valves.

The system incorporates a vane-type camshaft phaser that changes the angular orientation of the camshaft, thereby adjusting the timing of the intake and exhaust valves to optimize performance and economy, and help lower emissions. It offers infinitely variable valve timing in relation to the crankshaft. The cam phaser vane is attached to the camshaft on the front journal. As driving conditions warrant, the cam phaser system can reduce ignition timing at higher rpm levels to increase power. At lower rpm levels, torque is enhanced with increased timing.

This cam phaser feature was pioneered by GM and introduced on the new 3.5L and 3.9L V-6 engines in 2005 – a first for the use of variable valve timing on a cam-in-block engine design. As driving conditions warrant, the cam phasing system can reduce ignition timing at higher rpm levels to increase power. At lower rpm levels, torque is enhanced with increased timing.

Precise camshaft timing is the key to the variable valve timing system’s capability to optimize performance. Like the 58X ignition system, cam phasing is directed by the E38 ECM. It relies on data from a camshaft position sensor – a target ring with four equally spaced segments – that communicates the camshaft’s position quicker and more accurately than previous systems that used just a single segment. Also, a leaf spring-type tensioner is used on the timing chain to ensure precise tension.

The aluminum-block 6.0L version uses variable valve timing in conjunction with Displacement On Demand technology to bolster fuel economy. With cam phasing, Displacement On Demand technology allows the engine to run longer in fuel-saving four-cylinder mode, while producing instant V-8 power and response as soon as the driver calls for it."

Yogi Bear

Great explanation. Thanks, Bill!

KY_BOB

iTrader: (2)

Yes, it was but it sounds complicated.

04Denali

If you mean Displacement On Demand, Here is a good write up

http://www.superchevy.com/technical/.../0405sc_gmdod/

jblack6527

Great write up, and it's a cool idea, but just sounds like more switches and such to go bad..

02sierraz71_5.3

iTrader: (2)

Its gonna be interesting to see this setup with an aftermarket cam, might help get away from having to run a higher stall
I just wonder about P/V if youve got a cam with alot of duration and lift then the phaser drops the ICL.

How would you check P/V with a system that can infinitely adjust cam timing?
can you limit the amount the cam can be advanced/retarded with the pcm?
can you change the ICL manually, using the pcm on the stock cam?

eallanboggs

iTrader: (1)

OK, I now realize VVT and AFM are not related. Is it really worth it for the small gain they claim they are getting. I think it's 8% and I don't know if that's attributeable to VVT or AFM or the two of them combined. The photo I saw shows the VVT phaser mounted on the cam timing sprocket not the front journal which makes sense if it is controlled by a clutch like device. They could activate VVT or deactivate anytime they want that way. It's the Active Fuel Management that will affect the aftermarket parts business more with special lifters and solenoids in the lifter valley. Solenoids don't like a lot of heat and the lifter valley isn't the coolest place I can think of. If you are keeping both valves closed at what point in the 4 stroke cycle do you close them? The injectors must be disabled when the solenoids are disabled and what about the coil packs on those cylinders? Are they just dead fired? When they say high pressure oil do they mean higher then other places in the engine or does the new oil pump provide this "high pressure" throughout the entire oil gallery? This is a whole lot of gizmos that can go wrong, but they must believe in it because the 07s now have the 5 yr/100,000 mile warranty. Even so I leaning toward buying a 07 Classic Silverado as they are calling it so I know I can install all the parts off of my wrecked 04 on it without problems.