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Is it common to advance the cams on a 968?

Wondering if this is something you guys are doing?

I understand why people do it on older 4-cylinder cars, to move the powerband down in RPM and access the torque earlier.

I figured this is probably done on 944’s.

But with VarioCam, I did not think this would be necessary on a 968.

Curious on your thoughts about it.

Thanks!

Old 07-08-2018, 08:54 AM
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VarioCam does it for you. No need for you to do it yourself.
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Old 07-08-2018, 11:59 AM
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Variocam makes it unnecessary, the adjustment in that system is way more than an adjustable gear.

On an S or S2 it might make An interesting difference.
Old 07-08-2018, 12:02 PM
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Doesn’t VarioCam reduce the lift and retard the timing for economy and only increase lift and advance timing at wot?
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Old 07-08-2018, 01:03 PM
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Ok, so if you take your 968 to a shop, and they go ahead and advance the cams FOR YOU without asking...

... what’s the result? Should not be any mechanical problem, so to speak, I would think? Just a goofy thing to do.

My goal is to re-set the cams to factory position.

Just wondering if this is something that 968 guys do, and if there is any resulting negative issue, especially a damaging result.
Old 07-08-2018, 01:37 PM
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Never heard of it being done on a 968 however it has been done on non-variocam 928 4v cars.

The sprocket is adjustable so it's possible to try different settings if you like. The critical setting is to degree in the intake cam with the variocam pumped up however I think most people just make matchmarks and set the timing back the way it was. This could be a bit off if the head was skimmed or there is wear affecting the cam chain/sprockets.

Setting the Camshaft Timing on a Porsche 968

It is not possible to crash the valves within the adjustment window.

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Old 07-08-2018, 02:29 PM
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Quote:
Originally Posted by Jfrahm View Post
Never heard of it being done on a 968 however it has been done on non-variocam 928 4v cars.

The sprocket is adjustable so it's possible to try different settings if you like. The critical setting is to degree in the intake cam with the variocam pumped up however I think most people just make matchmarks and set the timing back the way it was. This could be a bit off if the head was skimmed or there is wear affecting the cam chain/sprockets.

Setting the Camshaft Timing on a Porsche 968

It is not possible to crash the valves within the adjustment window.

-Joel.

That is a really great answer. Thank you.

I did not realize the sprockets were adjustable from the factory. Do they have marks on them for returning them to original factory setting?
Old 07-08-2018, 05:35 PM
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Usually just marks from the fasteners being tightened down but you might have more than one set of those marks at this point. If a shop just let it flop one way or the other there might be marks in the middle somewhere and your setting might be at one end of the adjustment, so the middle-ish marks should be where it was set back when. The adjustment is not there to allow you to fool with performance but to time the intake cam relatively precisely, so when the sprocket goes on the zero setting is unknown.

I have a 928 where someone had the cam adjustment so far out of whack they had to pull one of the ignition rotor bolts off and run two. The car ran fine but obviously that was not a good situation. This setting is affected by cam belt and sprocket wear as well as belt tolerance and almost no one retimes the cams when they change belts so it's not usually super accurate but starting out with a setting that leads to acceptable timing with whatever belt and belt wear is best.

Maybe the factory procedure assumes the timing is best once the belt has been run-in skewing the cam, um, retarded? and is set with a little advance, a hot engine will skew this measurement also. I do not know how far the timing drifts over the life of the belt.

If a shop told me they advanced my cams I'd suspect they lost the factory setting when goofing with the cam-to-sprocket bolt and just advanced it, or claimed to, rather than realizing they had 3 hours of work to recover the factory setting accurately. Assuming they knew how to do that. I'd have to go in myself and see where they ended up and if I could find the factory marks or otherwise get satisfied with the cam timing, then send them a bill for a few hours of my time.

I think the first thing I'd do is pull the cam cover with the engine hot and check the timing marks as best I could with the engine hot, then let it cool overnight, spin the engine a few times, and check them again. Then you know the cold-to-hot skew on the basic sprocket markings.

At some point I'd pull the ignition rotor and check the relative position of the hub bolt holes inside the bean-shaped cam sprocket holes. If max'd out I'd suspect the shop was not doing a good job.

What were they up to when they goofed with this setting? Cam seal?
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Last edited by Jfrahm; 07-09-2018 at 06:26 AM..
Old 07-09-2018, 05:56 AM
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Quote:
Originally Posted by 9FF View Post
Doesn’t VarioCam reduce the lift and retard the timing for economy and only increase lift and advance timing at wot?
in a 968 it advances the intake cam 15 degrees(?) from around 1500-5500 rpm, doesn't mess with lift.
Old 07-09-2018, 08:43 AM
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Originally Posted by Jfrahm View Post
What were they up to when they goofed with this setting? Cam seal?

So this was done (under the previous owner) by a shop that is supposed to be regarded as a very knowledgeable 944 expert, and a shop that preps a lot of 944 race cars. He asked them to go through the car, almost blank check, and address all the common maintenance items.

According to the service record, they did a lot.... apparently basically rebuilding every part of the engine with the exception of removing the head or the pistons/rods/crank/bearings. Lots of gaskets, etc.

This area of the extensive service record says they went in and removed both cams, and the timing chain, replaced the timing chain tensioner pads, repaired the mounting threads for the chain tensioner (?), then reinstalled everything, and advanced the cams for “best performance.”

I’m trying not to digress and talk about how I don’t like this service record (because I don’t).

I’m trying to stay focused on why you would advance the cams, and what the result of doing so would be.
Old 07-09-2018, 09:47 AM
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i'm wondering if maybe they tweaked the "lift at TDC" specification which is something like 0.75mm in a 968. on the 944S it was 1.4mm, playing with this does wake the car up a little.

Old 07-09-2018, 11:09 AM
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