3900 Info

[CNCguy]

I have played with the VVT actuator just a little and IIRC, the default location is advanced and by applying pressure to the actuator the timing gets retarded.

If I get a chance, I will pull the actuator apart and get some pics of it's innerworkings this week.

[smilinguy99]

First of all, thanks for sharing all this information!

...As you can see in the last pic, there is no room on a 3100 for the 3900 head. The valves hit the top of the cylinder wall and the chamber overhangs the cylinder wall...

Within limits, the deck/bore can be notched to clear the valves and chamber.

[Scott_68B]

I'm usually a lurker here but I'm out of the closet to say that this is an AWESOME thread. Thank you CNCguy, especially, and everyone else for taking the time to research this.

-- Scott

[427v8]

Okay, I read that as actual valve lift by the cam. I really hope there is no problem running the engine without VVT or better yet that there is a way to activate it to stay at the maximum output setting which I guess would be full retard. I hope GM created a fail mode that favors best performance. The VVT is nice but all I really care for is the ~240hp/240 lb/ft and whatever height 7-10 psi will take that to.

I think you are mising the point.
The VVT increases torque at low RPM, that means more power can be had by using the VVT feature than by not.

Keith

[Joseph Upson]

I think you are mising the point.
The VVT increases torque at low RPM, that means more power can be had by using the VVT feature than by not.

Keith

No point missed, I know what it does, I don't want to have to wait until this issue is resolved to use the motor. In other words I want to install the engine now with VVT unplugged until a reasonable method of operating it without the OE PCM and 15 or so pages of wiring diagrams necessary for installing it is devised.

Our discussion about valve clearance is to make sure that unlike the Northstar with VVT, there will not be any piston to valve interference resulting from running the engine with the VVT mechanism disconnected.

[427v8]

Ah, I retract my statement.
I do agree, I want to use it also, but I didn't know or think about the valve to piston interference.

I am seriously considering the 3900 instead of the 3500 for my streetrod.
I would love to be able to run on 3 clyinders and use the VVT.

[CNCguy]

I would love to be able to run on 3 clyinders and use the VVT.

Be sure you get a LZ9, not a LZ8 like I have from an '06 Impala. The LZ8 has VVT but does not have the DOD feature.

[farmerz24]

No point missed, I know what it does, I don't want to have to wait until this issue is resolved to use the motor. In other words I want to install the engine now with VVT unplugged until a reasonable method of operating it without the OE PCM and 15 or so pages of wiring diagrams necessary for installing it is devised.

Our discussion about valve clearance is to make sure that unlike the Northstar with VVT, there will not be any piston to valve interference resulting from running the engine with the VVT mechanism disconnected.

i would imagine the reason that the N* will have piston to valve clearnace issues when deactivated is probably due to the fact that there are 4 cams to control, making for more possible combinations of piston to valve failure. I guess with the 3900 there is only one cam so maybe that is why it may work when disabled.

[Joseph Upson]

Be sure you get a LZ9, not a LZ8 like I have from an '06 Impala. The LZ8 has VVT but does not have the DOD feature.

I have about 7 engines within driving range to choose from, is there an external indicator or VIN code I can look for to determine this when I get ready for purchase?

[CNCguy]

I have about 7 engines within driving range to choose from, is there an external indicator or VIN code I can look for to determine this when I get ready for purchase?

Regretfully, I have no idea what to look for since I haven't seen the LX9. The GM site says that the LX8 was in Impalas and all others are are LX9. I know that this one is supposed to be from a '06 Impala and it doesn't have DOD. Actually, I prefer it this way since I unsure about the collapsable lifter being able to handle higher lifts and spring pressures. And I am not really worried about the gas since it is more of a toy than daily driver.

[Joseph Upson]

Regretfully, I have no idea what to look for since I haven't seen the LX9. The GM site says that the LX8 was in Impalas and all others are are LX9. I know that this one is supposed to be from a '06 Impala and it doesn't have DOD. Actually, I prefer it this way since I unsure about the collapsable lifter being able to handle higher lifts and spring pressures. And I am not really worried about the gas since it is more of a toy than daily driver.

Good point, it could very well be an added liability, furthermore I haven't noticed a significant fuel mileage increase above what's already advertised which I believe is still under 30 mpg hwy. With the compression ratio and oil squirters I should be able to squeeze at least 35 mpg out of it given what the guys on the Fiero site are getting out of the 3800 SC, 30+, and by activating the lean engine run mode in the TGP code and setting it for about 16:1 high miles per gallon at cruise should be very easy. I was told GM didn't activate it because of EPA sanctions not willing to accept apparently higher emissions in exchange for fuel savings.

[Joseph Upson]

Be sure you get a LZ9, not a LZ8 like I have from an '06 Impala. The LZ8 has VVT but does not have the DOD feature.

I just checked and you have it backwards, the LZ8 has DOD and the 07 Impala is the only one that gets it as observed on the GM site and it apparently debuted in 07 for the 3900, all of the 06 3900s are LZ9. I bet the Impala is the test bed so in the event it is a disaster they only have to deal with the Impala instead of the whole fleet of 3900 V6 cars.

[CNCguy]

I just checked and you have it backwards, the LZ8 has DOD and the 07 Impala is the only one that gets it as observed on the GM site and it apparently debuted in 07 for the 3900, all of the 06 3900s are LZ9. I bet the Impala is the test bed so in the event it is a disaster they only have to deal with the Impala instead of the whole fleet of 3900 V6 cars.

You are absolutely right... I should have read more.

[CNCguy]

Okay... So for you guys that are interested in the VVT actuators operation, I disassembled it today and took some pics. The center of the actuator is a valve that directs flow to advance or retard the cam. Total VVT travel is 27 degrees at the cam or 54 degrees at the crank.

There is a spring loaded pin that locks the actuator in the advanced position until pressure is built up to start operating the actuator. A spring is wound around the front of the actuator to help return it to the locked position and I assume to help override the drag of the cam while running.

Assembled VVT actuator on the cam without return spring


Cam Position Sensor tabs


Components of the actuator - Oil pressure valve & spring inside return spring.
Also you can see the spring loaded locator that locks the cam position when VVT not activated.


Actuator in "ADVANCED" position


Actuator in "RETARDED" position

[RacerX11]

I was told GM didn't activate it because of EPA sanctions not willing to accept apparently higher emissions in exchange for fuel savings.

That's just a nice way to say it was an illegal emissions defeat strategy.