3.9L LZ9 engine internal upgrade & performance?

[SappySE107]

What kind of engineer are you?

[NateD4]

You want more lift and less duration on a VVT cam compared to a non VVT cam, if you want to keep low end power and use the variable timing to extend that power to higher RPMs. VVT is a small factor to anything high performance, because the duration itself is needed to get more top end power. In terms of what the build is for, street/mpg, keep it small duration high lift with full VVT. Street/Strip add more duration and lift and limit the VVT travel. Race, bye bye VVT.

Why more lift and less duration on a VVT cam compared to a non VVT cam?

[SappySE107]

You want more lift and less duration on a VVT cam compared to a non VVT cam, if you want to keep low end power and use the variable timing to extend that power to higher RPMs. VVT is a small factor to anything high performance, because the duration itself is needed to get more top end power. In terms of what the build is for, street/mpg, keep it small duration high lift with full VVT. Street/Strip add more duration and lift and limit the VVT travel. Race, bye bye VVT.

[NateD4]

btw asking if it limits VVT isn't really the right question.

BUT to answer. yes duration limits VVT. More specifically it limits your advance/retard ability purely on geometry of the valves interfering with the pistons.

If you look at the valve timing in time. Then what you are gaining off course with higher duration is higher end HP. As a longer duration cam translates into more total time the valve is open at a given time. OR longer valve opening at higher RPM (technicallly at some RPM the total valve opening time is longer with more duration at a higher RPM than say a lower duation cam slightly lower RPMs.

The only gain I can see with duration is moving the power band up a bit.

Lift might be a different story.


My opinion....

[NateD4]

yes it does... sorta...

If you imagine the lobe centerline and on either side of it you have some degrees of valve duration then yes it will effect the max cam retard or advance angle you can use.

to exagerate if the valve is open 70 degree and you can run 20 degrees advance that means the cam is opens at 70/2 degrees + 20 degrees max advance. or 55 degrees. If you exagerate and go to 90 degrees total duration with the same 20 degrees of cam phase. Thats 90/2 + 20 = 65 degrees (relative to crank angle). As you can see the actual opening angle is greater with a greater duration. The closing angle is also greater (relative to crank angle). Of course in absolute terms that means the cam opens earlier and closes later with a longer duration....

So you have to verify the valves don't hit the pistons with the timing changes. If they do you have to limit the cam phase advance/retard from say 20 degrees to 16 degrees etc... If no piston to valve interference occurs you'll probably be ok.

[paramount]

SO does increasing duration limit VVT or not. I would like to know and I emailed mast motorsports since they make cams for VVT engines but they haven't got me back yet.

[robertisaar]

with that kind of range, it would be worthless. you can probably get that from chain stretch.

[ericjon262]

if you have to limit it to >2-3*, I imagine the gains wouldn't be worth the hassle...

[robertisaar]

my understanding was that in the LSx engines, you run into piston to valve clearance issues if you go to far.

this is probably true. i was more interested in the "why VVT would be useless" portion.

[ericjon262]

why? VVT is used to boost torque at all RPMs by advancing or retarding the cam to shift the powerband around. adding more lift and duration will favor high RPM power while sacrificing low RPM.

my understanding was that in the LSx engines, you run into piston to valve clearance issues if you go to far.

[robertisaar]

With enough Lift and duration the VVT would become useless.

why? VVT is used to boost torque at all RPMs by advancing or retarding the cam to shift the powerband around. adding more lift and duration will favor high RPM power while sacrificing low RPM.

[Kenova]

After looking at aftermarket cams for VVT LS engines I have noticed that as lift and duration increases the amount of advance and retard with the VVT is reduced substantially.
With enough Lift and duration the VVT would become useless.

Ken

[paramount]

The problem is finding someone who can do this cam for me. I plan on running somewhere around 11 compression on 93. Nothing crazy just would like to see a little gain on both ends.
I just posted here to find out if anyone found a solution to the VVT advance/retard woes.

[NateD4]

Not to shabby a torque curve. How much torque do we want/expect from a NA pushrod engine?

Certainly some cam changes, a bit of compression and a higher redline would give more power and slightly better torque.

[paramount]

I plan on bringing the car to a dyno tuner in SW florida. Says he has experience with G6's and uses HPtuners software on his tunes since he works with GM tunes only really (specializes in corvettes).
I don't need it to rev to 7K or anything, just 6500 would be nice. Have some nice low end grunt and then a little more high end. Just a little gain on both ends would be nice. Remember the engine
I have is really the LZ4 but I plan on stroking it to 3.9 with a 3.9 crank and custom pistons/rods.