....just got off the phone with the motorsports shop and got an estimate for my valve service and few other things. One of the items on my list is "weeping" cam timing cover. We discussed pricing for fixing the cover itself, versus taking apart the entire housing and fixing the gaskets at the base of the housing. (Obviously we don't know which gasket is the culprit yet)

The shop owner said that if we were into the cam timing cover, he could advance my timing and bump my performance up a bit. He went on to say that other 3.6L owners have been very happy with this "tweak". I was intrigued by his offer, but don't quite fully understand the tradeoffs. So I jumped on Rennlist and did search and didn't find any references to "timing advance". Can someone with far more mechanical knowledge than me shed a little light onto the process and what kind of performance improvement I could expect.

Thanks in "advance"!

 

Timing is totally controlled by the DME. The timing maps areloaded into the DME. I would interested to know how he is going to do this tweak. I would take care with this and get a full explanation from him before you part with your money. I will be honest and say I do not trust anyone who offers "these little tweaks" but that is just me.
Ciao,
Adrian
911C4

 

Er, timing advance with the timing cover off?? As ADrian suggests, spark timing is a DME issue. Maybe your guy is thinking of fiddling with the cam in some way - I would proceed with extreme caution...actually, I wouldn't proceed at all!!

 

Hmmmmm. Adrian's right (as usual) the DME sets the timing.

The person that I was speaking was the shop owner and a Porsche Certified Master Technician. I'm going to give him the benefit of the doubt and assume he had a brain cramp, confused me with another customer and forgot he was talking about a 964.

 

The mechanic may have been talking about cam timing, which is very different from the spark timing the DME controls. There is a procedure in the 964 factory manual that describes how to correctly time the cams. People have played with Porsche cam timing in the past, advancing or retarding it to try and impact low end acceleration or top end performance. I can't say I've heard of people playing with the 964 cam timing, but that's what comes to my mind.

 

Was your man not talking about the valve/camshaft timing as opposed to the ignition/fuel timing?

The former is a mechanical function (relationship between timing of the valves opening and the position of the pistons) as opposed to the latter which deals with the point at which the spark plug actually ignites the fuel/air mixture in the cylinder?

I did have fun once trying to set the cam timing on an old Lotus Elan after an engine rebuild! <img border="0" alt="[ouch]" title="" src="graemlins/c.gif" />

Didn't know that you could 'tweak' it on the 964 though - tread carefully!

 

Bill you beat me to it!

Interested to know whether this has much effect though.

 

This thread has already been very educational!

So we've got two types of timing here - ignition which is controlled by the DME and valve timing which is mechanically controlled.

I understand how a different cam affects valve lift and duration. How would "advancing" the cam timing affect the engine? (Be gentle guys, I write software for a living and have never torn down an engine before!) If understand things correctly (emphasis on IF), there are two cam shafts on each side of the engine. I'm assuming one cam lifts the valve for fuel and the other cam lifts the valve for exhaust. Can I logically assume that "advancing the timing" at the cam shafts changes (either shortens or lengthens) the time difference between the inlet valves opening and the exhaust valves closing (and vice/versa)?

 

Actually it's a pretty simple concept.

The cam belt provides a consistent mechanical link between the action of the valves (via the cam) and the movement of the pistons (via the crankshaft).

If you put the cam chain/belts on one tooth more to the left or the right you change the relationship of the the valve movement to the piston movement.

Note that it doesn't affect the duration of the open time of the valve. you would have to change the cam for one with fatter (or thinner) lobes to do that.

in overhead cam small Fiat engines advancing the cam - i.e. moving the belt to make the valves open a little earlier - made the engine a bit better at high revs but the totally gutless at low revs.

If I were you I'd ask to drive a modified engine defore letting him loose on yours !!!

 

Unless your mechanic is "creative", I think he's probably talking about changing the timing of the cams with respect to the crankshaft.

I did this on my MR2, but I think it was probably a lot easier. On the MR2 the access is better and I was dealing with a timing belt, not a chain. I got the impression that I was getting better low end torque, but on the other hand I was smelling a little more gas in the exhaust than normal. I set the timing back because I was concerned about possible long term damage to the catalytic converter and the possibility that the car would fail emissions. I also just liked playing with the car!! <img border="0" title="" alt="[Wink]" src="wink.gif" />

If I were you I'd do as at least one of the other posters said and test drive a car modified like that and also see what effect (if any) it will have on the emissions and the cat.

<img border="0" alt="[cheers]" title="" src="graemlins/beerchug.gif" />

 

Advancing the CAM timing on a 911 motor is quite EASY. It is described and suggested in Bruce Anderson's 911 Performance Handbooks, for all motors up to an SC 3.0L. - not sure he advises to do it for a 3.2 or not.

It's as simple as measuring what you have for advance at present, incrementing the cam sprocket pin one adjustment hole clockwise (from memory) and you have your next adjustment setting, which should advance your cams about .3 deg.

Your Mechanic was UNDOUBTEDLY speaking of bumping up the cam timing. Factory specs for a 964 3.6 are something like 1.1-1.2 deg. of advance...I could only guess the max you would want to advance them to is 1.4 deg. or so.

1.4 deg. is factory for an SC motor, suggested advance is to 1.7 deg. I performed this little "tweak" on my SC motor with fabulous results, gained a noticeable amount of low-end torque, didn't seem to lose much on the top, but theory is that you would.

NOW, my two cents on advancing a 964 motor...I wouldn't suggest it for TWO reasons:

1) The 3.6 motor in the 964 already has GOBS of low-end torque...why would you need more?? Do you want to break the rear end loose coming out of that hairpin turn?? My engine is set to factory specs (verified last year) and it already fishtails out of Oak Tree Turn at VIR, requiring a "spirited" steering wheel movement to keep from going in the weeds! <img border="0" title="" alt="[Eek!]" src="eek.gif" />

2) The 3.6 motor already stops "pulling" hard around 6500RPM and rev limiter is set to 6750 or something close to that...as the theory states that, "you sacrifice top end to gain low end" from "tweaks" to the cam/valve train, ignition timing, etc.

WHY WOULD YOU WANT TO LOSE TOP END??

There you go, from someone who's performed the "tweak", in my SC and who wouldn't imagine wanting anymore low-end torque in his 964.

NOW, I must add that I have a Cup Lightweight Flywheel/Clutch setup, I'm certain it's responsible for a considerable amount of low-end torque, being that once I installed it...there was quite the difference in acceleration.

SO, if you really think you would like more low-end torque...go for it, but consider leaving it to factory settings.

 

After the initial feedback from Rennlisters, I spoke to my mechanic again for further clarification. (It's ironic his clarification sounded earily similar to Jeff's reply!) He confirmed that he is indeed talking about advancing the cam timing, not spark timing as Bill and Jeff have indicated.

The offer to advance the cam timing was put on the table IF we have to replace the bottom seal of the cam timing cover to fix a leak. My mechanic is suggesting a cam timing tweak of 1.4 degrees for improved torque.

I haven't made my mind up on this one just yet, though this thread has been VERY helpful.

For the sake of exploring this thread a little more, I play devil's advocate!

Axle twisting, stump-pulling torque is something that you can use every day! My C4 is a daily driver and weekend warrior. Despite my best efforts along the Florida Turnpike, I just can't get my car over 120 during my daily commute! Though I do try! <img border="0" title="" alt="[Wink]" src="wink.gif" />

To Jeff's point about breaking the rear-end loose with more torque, remember I'm driving a C4 and only wish I could break the tires loose! With an extra set of wheels putting the power to the ground, I think I can put the torque to the pavement.

As far as losing some from the top-end, I'm OK with that. First, the majority of my track events are autocross or relatively speaking "low-speed" events. Second, I'll admit it, 150MPH+ is scary sh*t! IMHO, an incident at that speed is not survivable. And lastly, I believe that I need a lot more skill and confidence before I drive that fast.

....and there you have it - my perspective on torque vs top end!