Variocam engagement abrupt

I did a search but only found one reference to this question, and it was from 1999Porsche911, so I've gotta take his response with a grain of salt (yes, it was an oil thread). OK, I'm coming from a 993 (hence my handle) but now have a 2002 996 cab C2 with about 25K miles (but new to me). I notice that the variocam engagement is quite abrupt around 3200 RPM, especially in first gear and with light throttle. I know, someone's going to reply "use more gas!" but I drive in traffic a lot. I never experienced this with the 993. So, is this a normal thing that I need to learn to live with? Or is it one of those things, some cars do it, some don't? Or is it actually worth a trip to the dealer (and can they do anything about it)? Thanks all for your comments. Michael

Michael - I have an '04 C2 Coupe and yes, the variocam does "kick in" at about 3200 RPM. I noticed it more when I first got the car, but now I don't really notice it much at all. I don't think it has actually gotten "smoother" as it kicks in, but rather, it is probably that I am getting more "comfortable" and familiar with the car. BTW - where in NC are you located? I'm in Concord, just Northeast of Charlotte.

Thanks for the quick reply, glad it's not just me! I'm in Cary, near Raleigh. Michael

Try this search link , there's a bunch of returns that you can read through, particularly here , here , here , and here .

I'll confirm this too. Normal. I also agree that while it bothered me at first, I barely notice it now.

I have never "felt" this, but then I have no idea what it would feel or sound like.....can anyone expand?

The engine briefly runs less than smoothly for a moment passing through 3200 rpm. I believe it affects 2002 and newer and that there were some software changes in 2004 to try to make it less noticeable. It is most noticeable at light throttle.

Michael, I am in Cary as well. Would be happy to check it out for you. We could even compare cars and feel the VC engagement.

Dell, do our cars have VC issues? I thought it did not fashion itself in pre-2002 cars.

I haven't heard of a VC issue to date.

Guess I will be back and forth around 3200 rpm on the drive home tonight to see if I can feel this

While maintaining a constant (but moderate) level of acceleration, you should feel a little more �torque pull� around 3200 RPM (+/- 100 RPM).

I can feel it too, almost like a small boost. I also hear it engage.

Correct, it only occurs on 3.6ls w/variocam plus.

Hey Dell, thanks for the offer. It seems that enough people agree here that it's "normal operation" and so I'm not going to sweat it. Michael

No problem. Let me know if you change your mind. Cheers,

Happens to mine as well - interesting stuff. VTEC baby!

My 02 does it too but I feel it most in 5th or 6th on light acceleration. It is just noticeable if you look for it, I think it's normal and just something to get used to.

Same in my 03

If the car had 700HP it would be an issue. But at 320, it doesn't make it hard to drive. It's just the power that you've been waiting for.

normal for me too in an '02. became smoother when i switched to 5W-40 oil.

That drove me nuts for a while (03)... It still bugs me because I'm often cruising at 3200 or thereabouts in 6th on the freeway, so I can feel it all the time. I wish I could "move" the activation point 300 RPM north !!! I'd probably never feel it then.... It's always when crusing at light throttle that it's noticeable...

Ah - so that's what I'm feeling. New owner here and sometimes, only somtimes I get a little on-off feel. I hadn't really noted what revs I was at - I'll feel that out soon. Wasn't bothering me too much, but since a buddy of mine just had a catastrophic IMS failure in his 2003, I am hyper sensitive to every little thing! What oil did you switch from? Or is this just a ploy to get 1999Porsche911's goat? FWIW - I'm going with 5W50 Mobil1 when I do my first oil change...soon.

some of you guys are assuming that the smoother feel means better - it may, it may not, no one really knows for sure

Yeah, that is why I just laid down $3400 smackaroos for a 4 years, 100K miles, 0 deductible, dealer sponsored extended warranty when mine expired last month ! Not cheap, but cheaper than a new motor someday and peace of mind until I can afford a used 997 with GT3 aerokit ;-) I read somewhere that since variocam + uses engine oil for actuation, thicker oil like 15-50 or 20-50 was not recommended by the factory. I think 10-40 mobil one is IT... so it makes sense that 5W-40 would make it even smoother... It's an odd thing though, my previous 987 also has variocam I think and I could not feel this... I wonder if the 997 does it too !! Another glitch of the 996 to my eyes, is the sometimes abrupt clutch operation (pressing or releasing). It's not me, I've driven nothing but clutch smoothly all my life, but now and then it feels like I am shocking the drivetrain on the 996 when I press or release the clutch pedal, a little "doink", I think it is related to the above, it might be when I release the clutch and the RPMs land on the variocam activation "rpm range". Just a guess... The car checked out everytime I mentioned this to a dealer or mechanic !

Hi, Is this something you can feel thru all 6 gears? Or in a tip? Elaborate please.....thanks.

I believe he ment he switched from 0W40 to a higher viscosity. In most cases (all that I have seen) the timing change is much smoother going with a higher viscosity oil. Smoother as measured by feel and Porsche Tester by Porsche Technician plotting timing changes. I run 15W50 and cannot feel the changover and can cruise at the changover speed all day, nice and smoothly.

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

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

The thing is, it's funny how there are similarities between VTEC and variocam (essentially same tech, no?) except the VTEC doesn't have this "Abruptness" so it must be better - how about them apples rennlist?

The change in abruptness is because of the ability of the thicker oil to maintain lifter pressure better at the time of the change.

1999, what do you do for a living and what's your Porsche history? If you don't mind me asking

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.

i waspreviously running 0W-40. i use the Porsche approved oils as my guide line. (0W-40, 5W-40, 5W-50). just my choice, others have there opinions.

These have hydraulic lifters, not solid which cushions the change in lift. 0W40 often cushions it too much.

>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 ;-)

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.

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 ;-)

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

Although the thinner oil may get into the lifter faster, and oil pressure plays an important role in getting the oil in there, compression plays a bigger role in the oil leaving the lifter and therefore, the thinner oil will leave sooner. The shifting of the cam increases the valve lash temporarily, causing the jerky feeling.

Just FYI, that PDF I put on the web is 12MB and the server is acting kinda sluggish.

I'm pretty sure most here have not driven a VTEC car like an S2000 Ben. By comparison the Porsche system is very smooth.

Bill, If I'm not mistaken, what people are feeling at 3500 is the valve lift. The timing shift is somewhere between 5800 and 6200. It's what's happening when you see that big dip in your dyno chart. 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.

if you're talking about WOT, yes you can't tell in the porsche just like vanos in the M cars. i will say that the F22C in the S2000 is very smooth even when powering through WOT. i'm a Honda engineering fan. 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.

The chain tensioner scheme is for the non-Plus version, no?

That service manual is awesome - thanks for posting!

What you are feeling "later" at about 5200 rpm on the NA engine is the length of the intake becoming longer. The resonance flap opens wide at 5200 rpm creating a turbulance in the air flow that creates the feeling of a kick.

Aren't all 3.6Ls Plus? Maybe not. I know the 3.6L we put in my race car still used the tensioner. I know this because we had to modify the cam sensor ring and add an rpm switch to control the timing shift. Once we got it right it worked perfect but it was a pain. 1999, it is definitely the cam timing shift that causes the HP drop. If you look at the "before" dyno on the plenum thread you can see it happen. At least in my car the resonance flap didn't have much effect. We unplugged it and it had no impact on the dyno. Go figure.

If it was operating correctly, the resonance flap sure will effect the dyno. Just plot your timing and you'll see where it changes.

As far as I understand it, yes, all 3.6s are Plus. Check out the link I posted earlier. It shows the timing adjustment scheme is on the end of the sprockets. Not the sliding tensioners. Bill

I'm sure you're right. I must be confusing my engines.

All 3.6's are VC plus...

+10! Freakin sweet piece of literature to go with my 2002 Carrera. Where did you get this?

I don't remember. Possibly from the Porsche factory service website, Sweden. Bill

I have stayed out of the oil debate but this thread shows a very important part of why I stay with the factory oil specifications. The Variocam plus system is HIGHLY dependent on oil temperature and viscosity.

Every moving part of the engine is HIGHLY dependent on oil temperature and viscosity.

I've always noticed the Variocam kicking in between 2500 and 3000 rpms, but this is with an 02'. Keep in mind that the 99-01 cars have a much simpler system. They only have variable cam degree on the intake only. The 02+ have variable cam degree on the intake and exhaust, in addition variable lift (similar to Honda's VTEC system). Hence why the newer system is call "Variocam Plus". The operation of both systems is completely dependant on engine oil. Even a small deviation from the correct engine oil viscosity can easily cause problems with the engagement of this system.