LZ9 Manifold on LZ4 Motor

[60DegreeVVT]

Hello all... i have been posting this question on my home boards but i am getting little support. My question is this....

The LZ4 and LZ9 are basically the same motor. Yes the LZ4 is the destroked version of the LZ9 and they do both have VVT. What is the second difference is the Intake manifolds. from what i have been told the LZ9 manifold is...

The 3.9 is a dual runner or variable length design, one set of long runners for improved torque at low rpm but switches to short runners for high rpm flow. Since the 3.5 and the 3.9 use the same block and heads there should be no problem physically bolting the 3.9 manifold to the 3.5 motor.

The bigger question is, how is the variable length manifold controlled? Is there any way for the 3.5 motor and ECU to properly operate the manifold? Without proper control of the manifold there wouldn't be any benefit, it would always be in one mode. The manifold is no doubt tuned for use with the longer stroke of the 3.9 so that also raises the question of whether the 3.5 would realize the full benefits even with proper control.

Can someone please assist with this possible swap?

Can anyone please validate the quote above?

Would this swap be worth the hassle?

Thank You in advance.
Ryan

[robertisaar]

whoever wrote that did know what they were talking about... i'm trying to come up with a controller based on an Arduino that controls both the VI and the VVT, but that won't happen for quite some time.

if you wanted more low-rpm torque, then close the short runners using the tuning valve and keep it there(how is your call)
if you want more power at higher RPMs, keep the tuning valve stuck open.

i'm not sure how the factory PCM would react to it, but it is possible.

[60DegreeVVT]

so what you are saying is that i have to find out how the LZ9 ECU handles the manifold... how it monitors the long and short.... they must be vacuum controlled?

Thank You for the input so far.

[bszopi]

The vane (the part that switches between the runners) is controlled by a motor, which receives power from the PCM. Therefore, it could be based on any number of variables that the PCM is input, from vacuum, to RPM, to airflow via the MAF, etc...

BTW, welcome to the site!

[60DegreeVVT]

Thank You for the Welcome... i guess i should post an introduction...

And thank you for the info on how that intake manifold works.

i think that if i can get someone to tune the 3.5 computer to think it is a 3.9

[pocket-rocket]

Thank You for the Welcome... i guess i should post an introduction...

And thank you for the info on how that intake manifold works.

i think that if i can get someone to tune the 3.5 computer to think it is a 3.9

A better way would probably use a 3.9 computer and tune it for the smaller displacement, then it has all the correct provisions in place for deciding when and when not to move the vane. I'm not sure how easily this would be accomplished since I still don't know how to tune yet. I have the concept down and know what's going on, but I've never really messed with fuel/spark/VE maps, ect. I kind of like my engine in one piece, so I haven't changed anything in my chip besides the speed limiter to show my nephew, ect.

[TurboGTU]

easy way i see is seting it up like the old vortec or the 89-94 ford taurus SHO. Just rpm based. Using a circuit like this http://www.rx7club.com/showthread.php?t=233381 and using a vacume actuator or motor controller.

On the tune, just mess with the spark advance.

[CNCguy]

I have an LZ9 and thought the VI would be great but am now planning to do just the opposite. My neighbor has a friend who is an engineer at GM. He has been involved with GEN-III and newer 60V6s, more specifically the LX9 design. I was fortunate enough to see some prototype parts including what was probably the first LX9 UIM that was made using rapid prototyping. In some competition between different departments, the LX9 was able to produce more power than the LZ4. Long story short, his recommendation was to dump the LZ9 intake in favor of the LZ4's for best performance.