[Rutger Gert-jan]

Hi,



Last month I bought the 911&porsche world magazine, the one with the 968 buyers guide...while reading I found out that when the Vario Cam coil does not work correctly the engine could lose up to 75 HP. Just being curious what a difference the coil would make I pulled the connector and guess what, I did not feel any real difference in performance...just to make sure I handed the car to my father, first with the plug disconnected and then with the plug correctly installed. My father noticed a little difference but not that much as mentioned in the magazine. Is there a way to test the Vario Cam coil?? or is there another procedure to check it is working as it should? Is it also possible to check the voltage at the plug? i.e. if the correct voltage is reaching the plug?



Thank you in advance,



regards,



Rutger

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[rustech]

75hp sounds impossible. I don't see that happening. The S2's with virtually the same motor, but without the variocam and intake manifold design, made like 25 hp less. I've read many that have reported only a minor change in power when disconnected.

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[94SilverCab]

I don't know about 75 hp, but you should absolutely FEEL the variocam kicking in at 4,500 rpm...

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[rustech]

Even an S2 feels like a dog below 4,500rpm, Alot of that FEEL is the nature of a 4cyl. But yes, the variocam could be responsible for anything up to 25hp which to anybody that DRIVES their car, is detectible.

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[ds968]

4500 rpm ?! Now you guys are making me wonder if there's something wrong with mine which has always kicked in around 4100-4200 rpm <img src="/forum/images/smilies/968/unsure.gif" class="smilie" alt="" />

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[jaap]

In the past I have also tried whether I could feel the difference between running with the variocam disconnected and connected and I must say I could not. I verified operation of the coil by manually applying a 12V differential and could hear it activate (with the engine off). Also when you supply the variocam with power at idle the engine stumbles which to me means the mechanism works (changes timing when it shouldn't). The default (fail safe) state of the variocam is not activated which matches the correct timing for idle and high rpm. As far as I know the DME, based on all sorts of operating conditions, will activate the variocam anywere from 1500 to 2900 rpm and deactivate at 5500. So the kick you feel around 4200 rpm is not directly related to the variocam activating? The only thing I still want to try is hook up a light to monitor the exact time of activation and see if I can then feel it kick in.



Jaap

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[Renalicious]

Here is something I would like to see: would the variocam 4K rpm "kick" show up on acceleration charts? And on average, would you be able to actually see the difference between a motor that had variocam connected vs one that had it disconnected or malfunctioning.

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[Darryl]

[quote name='ds968' post='35432' date='May 12 2007, 01:17 PM']4500 rpm ?! Now you guys are making me wonder if there's something wrong with mine which has always kicked in around 4100-4200 rpm <img src="/forum/images/smilies/968/unsure.gif" class="smilie" alt="" />[/quote]



I thought 4200 RPM too! That's about where I can feel something...



- Darryl

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[ds968]

I recall the 4100 / 4200 being the point even before I put the new chip (Speed 6 Racer X ) in, so it's not as if the chip changed the point where the variocam kicks. I do feel another slight surge at 4500 or so and continuing from there, but it's not as pronounced as the one just past 4000.

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[jaap]

[quote name='Renalicious' post='35441' date='May 12 2007, 10:18 PM']Here is something I would like to see: would the variocam 4K rpm "kick" show up on acceleration charts? And on average, would you be able to actually see the difference between a motor that had variocam connected vs one that had it disconnected or malfunctioning.[/quote]





The "kick" or peak in the torque curve around 4k rpm is also there with the variocam disconnected, so this is not directly related to the variocam being activated. I remembered reading an article on this and found a copy on my computer and finally was able to find the source on 968.net (see Porsche Panorama, August 1992 where page 46 shows the graphs) which details all the 968 specifics. It shows that variocam can be activated anywhere from 1500 rpm till max 3k rpm and variocam will be returned to default setting after 5500 or below 1500 rpm. The kick around 4100 rpm is mainly the result of the intake resonance feature which appearenlty is effective from 4k and higer rpm.



Jaap

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[94SilverCab]

OK, I find this fascinating.



What you are saying JAAP is that the variocam will activate in a range anywhere fromn 1,500 to 4,000 RPM. The selenoind will rise/fall and change the cam timing through the acceleration curve dependig on conditions and does not, infact, "kick in" at a particular RPM?



The 4,000 RPM "kick" is solely from the intake shaping?



This was not my understanding, but it does make sense ands I would like others smarter than me to weigh in here.



Regards,



Jay

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[jaap]

Jay



As far as I understand the article and other discussions variocam is activated anywhere between 1500 and 3000 rpm. This means it is always activated between at least 3k and the 5.5k rpm where it return to its basic timing but could be active as soon as 1500 rpm depending on required engine load etc. I think I will hook up some sort of monitoring light to actually verify this during operation.



Jaap

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[PorscheDude]

[quote name='jaap' post='35459' date='May 13 2007, 06:51 AM']The "kick" or peak in the torque curve around 4k rpm is also there with the variocam disconnected, so this is not directly related to the variocam being activated. I remembered reading an article on this and found a copy on my computer and finally was able to find the source on 968.net (see Porsche Panorama, August 1992 where page 46 shows the graphs) which details all the 968 specifics. It shows that variocam can be activated anywhere from 1500 rpm till max 3k rpm and variocam will be returned to default setting after 5500 or below 1500 rpm. The kick around 4100 rpm is mainly the result of the intake resonance feature which appearenlty is effective from 4k and higer rpm.



Jaap[/quote]







I believe this is correct. Vario cam activates @ 1500 RPM and deactivates @ 5500 RPM







Patrick

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[Renalicious]

Interesting, so variocam might not actually have as much of an impact as I thought <img src="/forum/images/smilies/968/ohmy.gif" class="smilie" alt="" /> I know the 968 engine has 25HP more over an S2 engine, but would most of it come from the intake then?

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[flash]

yup



the 4200 kick is mostly dual resonance intake related - it is very much like a turbo, and in fact provides 4psi boost



the variocam is at 1500 and 5500



the impact of the variocam is likely less than 10hp - i disconnected mine in a "test" and that's about what it felt like - noticeable but not the end of the world - what it does do is add torque down low and smooth out the curve across the board



i really like what pete's chip does to all of this - really makes everything pop like it should

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[94SilverCab]

[quote name='flash' post='35471' date='May 13 2007, 01:24 PM']the variocam is at 1500 and 5500[/quote]



What I'm questioning here is the word "AT" does the variocam come on AT 2 diferent times or does it function throughout the range...very curious.



Jay

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[Darryl]

[quote name='94SilverCab' post='35460' date='May 13 2007, 09:25 AM']OK, I find this fascinating.



What you are saying JAAP is that the variocam will activate in a range anywhere fromn 1,500 to 4,000 RPM. The selenoind will rise/fall and change the cam timing through the acceleration curve dependig on conditions and does not, infact, "kick in" at a particular RPM?



The 4,000 RPM "kick" is solely from the intake shaping?



This was not my understanding, but it does make sense ands I would like others smarter than me to weigh in here.



Regards,



Jay[/quote]



Jay...I too was fascinated by this as I thought it "kicked in" at a cretain point. I think what the article and others are saying is that the variocam is "active" all the time, as it is circuitry that is constantly adjusting the valve timing based on current driving conditions. There is no need for this "adjustment" below 1500 or above 5500 as you're either puttering along or going full bore and no need to computerize either one of those conditions.



- Darryl

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[jaap]

[quote name='Darryl' post='35476' date='May 13 2007, 09:47 PM']Jay...I too was fascinated by this as I thought it "kicked in" at a cretain point. I think what the article and others are saying is that the variocam is "active" all the time, as it is circuitry that is constantly adjusting the valve timing based on current driving conditions. There is no need for this "adjustment" below 1500 or above 5500 as you're either puttering along or going full bore and no need to computerize either one of those conditions.



- Darryl[/quote]



From the graphs I don't think variocam is "active" (ie switching) all the time, only the initial rpm point of activation may vary between 1500 and 3000 rpm depending on operating conditions and power requirements. Once activated it remains active until the engine rpm either go above 5500 rpm or drop below the lower rpm threshold value and always deactivates below 1500 rpm.



Jaap

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[doster]

There is a good description of how it works in here.

Procedure_for_inspection_of_Porsche_968_Camshafts.pdf Size: 988.9 KB  Downloads: 34

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[968workaholic]

The main idea of having a variable cam timing mechanism is to better time the intake pulses with the engines rpm and the amount of spark timing. Now i'm not 100% sure on Porsches, but on Mercedes engines that use an identical setup, the cam timing is reatrded and the air takes the shorter path through the manifold when the engine is idle +/-2,000rpm. The reason being it is easier for the air to take the shorter path and the engine load is normaly low at that rpm range, so the cam is retarded to burn the most of what is in the cylinder. However, above +/-2,000rpm until around 4,500rpm the cam is advanced and the air takes the longer path. The reason being that in the rpm range you want the air to have a high velocity to be albe to pack as much in the cylinders as possible, and that is what the longer path provides. The cams being advanced deals with the pulses in the intake from the longer path and works better at filling the cylinders. But, above 4,500rpm it switches back to the previous position that is used at idle (short air path and retarded cam timing) for the reason that you are no longer worried about keeping up the velocity at that point you just want as much air as possible to get in. The retarded cam timing helps with that by matching the intake pulses with the increased rpm. This is all dependant on load, temperature, and other factors, but that is the main idea of how it works. But i cannot imagine a 75 hp change from unplugging that solenoid. A 25 hp loss seems more reasonable.

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