3 chain, 5 chain question

[The Radium King]

necro.

so, here is a pic of a 5-chain engine:

https://www.pelicanparts.com/techarticles/Boxster_Tech/16-ENGINE-Camshaft_Swap_and_Chain_Tensioner/Gp1800.pdf

chain joins driveshaft to intermediate shaft. chains from ims to heads, chains join intake and exhaust cams.

next step - understanding variable timing and cams. there are THREE systems, variocam, updated variocam, and variocam+.

variocam was on all 9x6 until 2002. in 2003 986 got updated variocam, while 996 got variocam+.

differences?

variocam uses an actuator that pushes on pads that tension the chains joining the intake and exhaust cams. this tension changes the timing (advances/retards). it is not gradual, but rather on/off based on rpm (and designed to interact with the resonance flapper on the intake). the pads will wear (hard dark brown plastic in the oil pan) on the chains and will eventually need replacing with the updated porsche part. the actuators can also fail, resulting in drastic (ie, -16 degree) cam deviation and often green rubber in the oil pan. the solenoids and cam position sensors are also a failure point.

updated variocam gets rid of the chains joining the intake and exhaust cams (ie the transition from 5-chain to 3-chain in 2003) and uses a 'vane cell adjuster' mechanism on the intake cam sprocket to provide infinitely adjustable timing. this is the reason for the bump in hp in the 2003 986 models. since more sophisticated ecu control is required for this (ie, no longer just an rpm-based on/off signal) the cars moved from the 7.2 to 7.8 dme and this is why putting a m96.2 engine in an early car is such a pain. it does, however, do away with many of the moving parts on the earlier engines and there are fewer failure modes.

finally, variocam+ incorporates the updated vane cell timing adjustment with variable valve lift height; 987 cars did not see this until just before the dfi engine came out.

otherwise, the three chain engines may have issues not directly related to the change in cam actuation; for example, the 996 moved from 3.4 to 3.6 displacement and the 3.6 engines tend to have piston slap issues (the increase in displacement was achieved by increasing stroke, which increased lateral force on piston walls and really brought to light the inadequacies of the cylinder liner material being used at the time) and, porsche also changed something with the ims in and around the same time.