I've often wondered how the variable valve timing system on the 968s (and other cars) works. Can anyone point me to a FAQ about it or offer an easy-to-understand description of the system?

 

f-it

 

From what I understand, its varied by the tension or slack in the cam chain. Since we are talking about 16v engines, there are 2 cams. There is a chain that goes between these cams. This chain drives cam 2 off of cam 1. Cam 1 is driven by the timing belt like an 8v motor. Under the chain is a tensioner just like the s motors and the s2 motors. However in the variable timed motor, this tensioner can vary the tension in the chain. The difference in tension effects the valve timing. So at different engine loads, the tensioner is varied causing different valve timing.

 

It moves chain slack up and down to adjust the intake cam.

I googled '968 variocam' and came up with this:

http://www.porsche968uk.co.uk/porsche-variocam.htm

Nice site.
-Joel.

 

Wow seems overly complicated for the amount of insignificant gains. 6lb ft of torque and 5bhp? Or am I not understanding this correctly???

 

completely wrong!

it only changes the cam timing.

the tension/slack in the cam chain stays the same. the effective length of the chain changes.

it's a binary change in timing that is actuated by a solenoid that is controlled by the DME at specific RPMs.

the hp\torque gained is basically the difference between an S2 and 968. not sure of the exact #, but the 986 spec is 236hp.

do a search on 968.net for more info.

 

It's more like 28-29 extra horses... a worthwhile improvement

 

I think what is says is that it retards the intake cam for high end power, then advances it again close to redline. Without that flip/flop way at the top of the rev range it loses 5bhp. The 968 does have nearly 30 HP more than the S2, some of which could be attributed to the MAF, higher compression and bigger valves. However you don't just get more top end HP, but more area under the HP curve. The variocam makes all that other stuff more liveable too. It's a nice motor.

-Joel.

 

VarioCam, the exhaust cam is driven by the crank, and the intake cam is driven, via a short chain, by the exhaust cam. In order to advance and retard the intake cam, the chain tensioner on that short chain simply shifts up and down, moving the extra length in the chain from the tight side to the slack side. When the tight side has no extra chain (ie. the chain is straight), the intake cam is fully advanced, as more chain is shifted to the tight side, the cam is retarded.

Picture here

 

All i know, is its something i wont ever have

 

I thought all jedi's had variocam?

 

Ok, gotcha. Seems to make MUCH more sense now. And yes the improvement DEFINATELY sounds worthwhile.

Rock - "VarioCam, the reason for higher eductation."