3900 Info

[Joseph Upson]

Close but an 07 just to be on the safe side with the 6 spd automatic attached to it. The Rendezvous is all wheel drive I believe and the bell housing on that engine might be different from the 07 now released for the G6 and a couple other FWD cars. The 07 also has higher horsepower and rpm ranges than the 06. I'd be interested to see if it takes up as much room as the 3.4 DOHC, from other pictures I've seen it looked like GM trimmed the heads down some.

[Joseph Upson]

Is the front of the block tapped for the plate used to prevent the cam from walking? and does it appear to be possible to retrofit the non VVT valve train components for use by increasing the length of the timing chain a notch to make up for the change in cam location?

Never mind I recall there being a difference in cam bearing size

[Joseph Upson]

How does the VVT appear to function, I get the impression it has a hydraulic component?

[CNCguy]

How does the VVT appear to function, I get the impression it has a hydraulic component?

The VVT is operated by hydraulics but controlled with an electric actuator. The actuator pushes a valve in the center of the hydraulic unit. I am still trying to find what kind of signal is used to operate it. It only has two wires, so I am assuming it operates on a DC voltage.

I am planning to make either a gear or an adapter to eliminate the VVT feature for those who want to install in cars with limited space.

[Joseph Upson]

Two wires suggest it's a function of variable voltage, perhaps a potentiometer linked to the throttle to advance the cam in the appropriate RPM range would be even better considering at a minimum the cam would have to be installed straight up to get at least the normal range of power.

[CNCguy]

Two wires suggest it's a function of variable voltage, perhaps a potentiometer linked to the throttle to advance the cam in the appropriate RPM range would be even better considering at a minimum the cam would have to be installed straight up to get at least the normal range of power.

I assumed variable voltage also but do not know if there is a direct relationship between voltage input and cam timing or if cam timing is constantly calculated by the PCM using feedback from cam/crank sensors and voltage is varied to make required timing changes. If there is a direct relationship, a small controller could be built that would control the actuator using RPM & MAP inputs. Perhaps the same controller could handle the variable intake also.

Between work and some other new products, I haven't had much time to spend on this issue. I was hoping that someone would jump in with some accurate info on how the VVT & variable intake control systems operate.

In case you're interested, the electrical actuator for VVT has around 7.5mm of travel.

[Joseph Upson]

7.5 mm is a good bit, my guess would be that the baseline is set at maximum low end torque efficiency and then advanced from there with rpm increase. I no longer have my trigonometry book to help calculate the number of degrees that would translate into but I wouldn't doubt it's close to a 1:1 ratio. My curiousity now would be if there is any serious advantage to be gained if the cam were reground to higher performing specs in addition to the VVT function.

Given the knowledge of the potential for interferance with the valve train I imagine you would need to know the clearance between the piston and the valve at full retard and advance before making such a move on a $400 cam.

[bszopi]

I'll see if I can't dig up any info, either via some GM contacts or other means...

[CNCguy]

I'll see if I can't dig up any info, either via some GM contacts or other means...

Sounds good Brad... hopefully you will have better luck that I've had.

[AutoTech]

Any updates?

[bszopi]

Not sure if this will be of any help, but here is a response I got from one of the GM engineers...

My experience is in the VVT system and not the variable intake valve.
Like fuel injectors, the VVT system works with Pulse Width Modulated
(PWM) electrical signals. Older PCMs would not have the built-in drivers
to generate this signal. Your member is correct in the description of the
close-loop feedback control system that is used to monitor measured cam
position relative to the crank position and constantly correct by it
changes in duty cycle to reach a desired set point. The are many inputs
into the determining the desired set point and a lot of calibration
settings on how fast to get there. Boxes can be and have been built.

[Joseph Upson]

Not sure if this will be of any help, but here is a response I got from one of the GM engineers...

In that case can it be assumed that the cam will run straight up in the event of a phasing system failure in an effort to maintain flawless driveability minus some horsepower and torque as well as in the event someone drops the engine in a non VVT car?

Since it's basically pulse operated like an injector if I understood it correctly, a basic stamp computer should be easily programmable for rudimenary function of just varying pulses to advance or retard based on rpm and throttle position. I have programmed one to pulse a fuel injector and that was pretty easy.

[bszopi]

I'll see if I can find the default. I also want to see if I can get a listing of all of the parameters that are used in determining the phasing...

[Spankdamonkey]

There's definitely a significant amount of changes made to this engine compared to the 3400/3500. There are some pics on here somewhere of a cut-away engine display I took at the north american international auto show. The top end will NOT bolt to earlier engines though. Due to the unique shape, size, and position of the ports on the upper and lower intake manifolds they can only be used with the 3900 heads. And the 3900 heads can't be used on earlier engines because the 3900 has offset cylinder bores.
It's obviously a technological jump from the older engines, but IMO the 3900 still doesn't make enough HP considering the half liter displacement increase, variable cam timing, and everything else. Especially considering the HP from competing manufactures V6's that are only 3.5L. They should have been able to get more from it.

Sorry to revive a post, but what you're saying is that a top end from, let's say, a 3400 won't bolt up to the 3900 block due to the spacing of the cylinder bores??? There goes one more "brilliant" idea

[CNCguy]

Sorry to revive a post, but what you're saying is that a top end from, let's say, a 3400 won't bolt up to the 3900 block due to the spacing of the cylinder bores??? There goes one more "brilliant" idea

Actually, we mounted a 3500 head to the 3900 engine and it appeared that the holes were in the correct locations. The problem is that the combustion chamber is not centered with the bore. GM moved the cylinders out 1.5mm on each side, making the block and heads wider. Whether it would be capable of running that way, I do not know. You would want to keep the 3900 top end anyways.... much bigger ports and valves.