Variocam on Turbo engines

[Bergerac]

Im interested to see what paths people have taken with regards to Variocam when using the 968 on a 16V turbo engine.

- Have you retianed the stock cams and adjusted the activation points?
- Are you running upgraded cams with variocam?
- Have you deleted the variocam and gone with a S2 chain tensioner or dual pulley setup?

Im having a few issues with a rattle from my tension at idle when the car is hot (not here to solve that) but Im almost at the point of deleting it all together, a refurbished tensioner is $1800 from Porsche with an exchange (so the car will be off the road untill it arrives) its not much more expensive to get some fresh cams and a dual pulley setup from Catcams and never have to worry about pads and chains again.

[Thom]

- yes / yes
- no
- no

On my road engine Variocam makes a subtle but worthwhile difference in overall drivability and performance. Whether it would be needed on an all-out race engine is not certain, especially with aftermarket cams using "more" overlap than stock. I believe the effects of Variocam will vary significantly depending on the compression ratio/cam profile combination.
On a stock 968 engine I believe the upper switch point was set to maximise VE within the resonance modes of the specific 968 intake manifold where the length of the air path was maximised with all the room available in the engine bay.

Happy New Year btw.

[Bergerac]

I've definitely seen a drop off of VE around the deactivation point while tuning at low boost, Im planning on raising it or even disabling it, since I'm running very short runners.

I'm struggling to understand why the tensioners are so expensive to refurbish, there should be very little mechanical wear since they're filled with oil, there is just some old hard seals and a couple of tired springs to replace. There is only so many low mile units left.

[Bergerac]

Disassembled tensioner

[Thom]

Thanks - first time I see one of those apart.

Not sure if discussed already but did you check the ball + spring valve assembly in your 968 head? Rattling from the chain could be caused by too little oil pressure to the tensioner.

[ROB III]

@Bergerac
I'd agree it doesn't look terribly complex.
Some of the possible reasons for cost:

Manpower cost to dissassemble and inspect and reassemble
Internal Handling
Testing to ensure a rebuilt meets original spec
If NOS of the whole tensioner is unavailable and/or some of the internal parts are NLA from the vendor supplying Porsche, reboot for the part$ gets $$
Shipping
Porsche profit
Just an opinion...but I agree with your question.

[Bergerac]

Thanks - first time I see one of those apart.

Not sure if discussed already but did you check the ball + spring valve assembly in your 968 head? Rattling from the chain could be caused by too little oil pressure to the tensioner.

I did have an issue with the ball and spring valve but it was rectified, I am about to mount a pressure sensor in the temp sensor location to confirm I dont still have a pressure issue. I have a new oil pickup as well so the obvious causes shouldnt be an issue.

[michaelmount123]

The Variocam system is designed and tuned for the NA 968 and effectively increases HP and torque by altering intake cam timing at specific RPM points along with several other factors. The energized Variocam (typically on at 1500 RPM, off at 5500 RPM) advances the intake cam by 15 crankshaft degrees and decreases valve overlap in the midrange. Net effect on a stock 968 is a significant increase in torque and HP over a non-Variocam configuration.

Once a 968 engine is modified, the standard (stock) activation points will likely no longer be optimized. In fact, aggressive performance cams typically work best with the Variocam deactivated and the cams timed in a static setting.

Determining whether to use the Variocam, or to determine revised activation points will require dyno testing.

Step 1: Test full RPM range with Variocam deactivated (solenoid unplugged) and chart results.
Step 2: Test full RPM range with Variocam activated (constant 12V to solenoid) and chart results.
Step 3: Overlay the two charts to see where (or if) the power crosses over between Steps 1 and 2.

You can then set the activation at the power/RPM crossover point or eliminate the Variocam timing change all together based on the relative power curves. This test addresses a full power application where max HP is desired. The crossover points may be different under partial throttle, but arguably not relevant here.

It's not rocket science, but takes a dyno, understanding the Variocam operation, safe mechanical operation at both activated and non-activated cam settings, and a desire to maximize performance.

Edits are in RED

MM

[944crazy]

I remember reading some old threads on rennlist where the variocam solenoid had been reversed on a boosted 968 so that the intake cam would be retarded 15 degrees in the upper rpm. The intended benefit was to reduce valve overlap in the higher rpms.

[michaelmount123]

I remember reading some old threads on rennlist where the variocam solenoid had been reversed on a boosted 968 so that the intake cam would be retarded 15 degrees in the upper rpm. The intended benefit was to reduce valve overlap in the higher rpms.

See my edits in last post.
For clarification:
The Variocam solenoid has the intake in its retarded position (increased overlap) under 1500rpm and over 5500rpm. A turbo engine often likes reduced overlap, but on a 968 with its relatively mild cams, only the dyno knows for sure.

I do think the 968NA cams are a fine choice with a turbo.