Variocam engagement abrupt
05-24-2007, 12:26 PM
#31
Race Car
Originally Posted by JimB
I'm not sure how thicker oil will smooth out the cam shift (good or bad Ben). There really isn't any magic going on. There is an on/off (not variable) switch that changes which cam lobes are used. You have two sets of lobes, a taller center as I recall with a shorter lobe on each side. You might be able to zoom in on the picture in the X51 thread and see them. I think the valves have to be being lifted by one or the other. I don't think there is an in-between.
When we put the 3.6L in my 1999 race car the computer didn't have the ability to shift the cams so we just put a switch on the dash and did it manually. Later I added an RPM switch it do it. We shifted them at 2500 which worked fine. The car runs great on the high rpm lobes except at idle.
Not sure why I wrote this. Just trivia I guess.
Jim
When we put the 3.6L in my 1999 race car the computer didn't have the ability to shift the cams so we just put a switch on the dash and did it manually. Later I added an RPM switch it do it. We shifted them at 2500 which worked fine. The car runs great on the high rpm lobes except at idle.
Not sure why I wrote this. Just trivia I guess.
Jim
The change in abruptness is because of the ability of the thicker oil to maintain lifter pressure better at the time of the change.
05-24-2007, 12:43 PM
#33
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Originally Posted by 1999Porsche911
The change in abruptness is because of the ability of the thicker oil to maintain lifter pressure better at the time of the change.
05-24-2007, 01:43 PM
#35
Race Car
Originally Posted by JimB
I'm not sure I follow that. The lifter is always contacting one lobe or the other right? It's not like they bounce up and slowly come down. So they are always being driven by either the tall lobes or the short ones I think. And like I said, it's an on/off switch that controls them. I sure could be wrong though. I'm better behind the wheel than under the car.
05-24-2007, 02:00 PM
#36
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>The change in abruptness is because of the ability of the thicker oil to maintain lifter pressure better at the time of the change.
See, that's the opposite of what I've read or heard... The Porsche tech was saying to stick with 0-40 oil, as recommended by the factory, because thicker oil (say 15-50) would mess up the smoothness of the transition ! I also read there was a software update that made it better, but the dealer never heard of it... Anyway, I don't know the technicalities, but I am glad to hear it's not just my car ;-)
See, that's the opposite of what I've read or heard... The Porsche tech was saying to stick with 0-40 oil, as recommended by the factory, because thicker oil (say 15-50) would mess up the smoothness of the transition ! I also read there was a software update that made it better, but the dealer never heard of it... Anyway, I don't know the technicalities, but I am glad to hear it's not just my car ;-)
05-24-2007, 02:52 PM
#37
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my two cents. hydrolic valves have narrow passages that the oil flows into. thinner oil flows easier in to these channels.
i imagine the thinner oil, 0W, allows the variocam to activate faster. the thicker oil activates a little bit slower making for a smoother cross over. this may compromise performance (delayed switchover) for comfort, i.e. smoother transition. everything has it's trade-offs.
the variocam as i understand it also includes a change over in the intake runner length which could also lead to an abrupt change over.
i imagine the thinner oil, 0W, allows the variocam to activate faster. the thicker oil activates a little bit slower making for a smoother cross over. this may compromise performance (delayed switchover) for comfort, i.e. smoother transition. everything has it's trade-offs.
the variocam as i understand it also includes a change over in the intake runner length which could also lead to an abrupt change over.
05-24-2007, 03:07 PM
#38
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On that note, I wish they had not set the cutoff at 3200 rpm, or thereabouts, or that it'd be moveable... If you drive in 6th on the freeways, that translates to about 80-85 mph, my daily average, so I am always cutting in and out of variocam activation... I either need to slow down or speed up ;-)
05-24-2007, 03:08 PM
#39
For those who aren't up on this, there are two aspects to the Variocam Plus.
One is the timing of the camshaft with respect to its drive chain. The other is the valve lift.
The lift is controlled by a coaxial hydraulic lifter. Switching between the two cam lobes is
a binary affair (at any given lifter).
Timing is controlled by oil filled chambers with vanes similar to the motors
in air tools and some power steering pumps. There's a nightmare of fluid
valving to control it. One can see how using the wrong oil could affect it.
(I'll leave the argument over what's right to somebody else)
I've uploaded a PDF that described pretty well how all this works.
http://www.wrljet.com/junk/2002_996.pdf
Starts on page 12.
Bill
One is the timing of the camshaft with respect to its drive chain. The other is the valve lift.
The lift is controlled by a coaxial hydraulic lifter. Switching between the two cam lobes is
a binary affair (at any given lifter).
Timing is controlled by oil filled chambers with vanes similar to the motors
in air tools and some power steering pumps. There's a nightmare of fluid
valving to control it. One can see how using the wrong oil could affect it.
(I'll leave the argument over what's right to somebody else)
I've uploaded a PDF that described pretty well how all this works.
http://www.wrljet.com/junk/2002_996.pdf
Starts on page 12.
Bill
05-24-2007, 03:11 PM
#40
Race Car
Originally Posted by UCrazyKid
my two cents. hydrolic valves have narrow passages that the oil flows into. thinner oil flows easier in to these channels.
i imagine the thinner oil, 0W, allows the variocam to activate faster. the thicker oil activates a little bit slower making for a smoother cross over. this may compromise performance (delayed switchover) for comfort, i.e. smoother transition. everything has it's trade-offs.
the variocam as i understand it also includes a change over in the intake runner length which could also lead to an abrupt change over.
i imagine the thinner oil, 0W, allows the variocam to activate faster. the thicker oil activates a little bit slower making for a smoother cross over. this may compromise performance (delayed switchover) for comfort, i.e. smoother transition. everything has it's trade-offs.
the variocam as i understand it also includes a change over in the intake runner length which could also lead to an abrupt change over.
05-24-2007, 03:59 PM
#42
Ironman 140.6
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Originally Posted by Benjamin Choi
now is the heavier oil making things better cuz it supposedly smooths it out or is the "abruptness" , which it really is not abrupt, the natural function/design result of porsche engineering?
not sure why people are insinuating that smoother is better inthis case
not sure why people are insinuating that smoother is better inthis case
05-24-2007, 04:55 PM
#43
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Originally Posted by wrljet
For those who aren't up on this, there are two aspects to the Variocam Plus.
One is the timing of the camshaft with respect to its drive chain. The other is the valve lift.
The lift is controlled by a coaxial hydraulic lifter. Switching between the two cam lobes is
a binary affair (at any given lifter).
Timing is controlled by oil filled chambers with vanes similar to the motors
in air tools and some power steering pumps. There's a nightmare of fluid
valving to control it. One can see how using the wrong oil could affect it.
(I'll leave the argument over what's right to somebody else)
I've uploaded a PDF that described pretty well how all this works.
http://www.wrljet.com/junk/2002_996.pdf
Starts on page 12.
Bill
One is the timing of the camshaft with respect to its drive chain. The other is the valve lift.
The lift is controlled by a coaxial hydraulic lifter. Switching between the two cam lobes is
a binary affair (at any given lifter).
Timing is controlled by oil filled chambers with vanes similar to the motors
in air tools and some power steering pumps. There's a nightmare of fluid
valving to control it. One can see how using the wrong oil could affect it.
(I'll leave the argument over what's right to somebody else)
I've uploaded a PDF that described pretty well how all this works.
http://www.wrljet.com/junk/2002_996.pdf
Starts on page 12.
Bill
The timing shift is also binary. If you power the switch, your cam chain tensioner is on one side, if you don't power its on the other.
05-24-2007, 05:05 PM
#44
Banned
Originally Posted by Ray S
I'm pretty sure most here have not driven a VTEC car like an S2000 Ben. By comparison the Porsche system is very smooth.
however, at partial throttle, you don't notice the switchover at all in the VTEC system whereas in the vario case, it sounds like people do notice the variocam since something is going on. maybe in the vtec system it simply doesn't hit the more aggressive lobes?... **** the name escapes me.
i hear though that the BMW double vanos is the most advanced. I'm loving their V10 in the M5/6. what's crazy is, i also hear that bmw will not CPO the V10 cars.