Camshaft Timing... (or how to gain 20 hp...)
03-22-2005, 11:51 AM
#1
Race Car
Thread Starter
Camshaft Timing... (or how to gain 20 hp...)
In the 964 the camshaft position was kept better in the factory measurement postion than in the 993. As a consequence there are discrepancies in the valve openings between the left and right cylinder banks. The opening distance is not documented by Porsche, but Porsche tuners have found out that the correct opening should be 1mm. An imbalance cause hp loss. My Porsche mechanic said that he has never seen a 993 with the correct and balanced valve openings. He has done the measurement and properly set the valve openings for many 993s, even for 993RSs and he said that each time he notices the engine becomes lively and he thinks that about 20hp can be recuperated. The problem afterwards, is to make sure that the camshaft retains the correct position and does not slowly drift away again. This can be done by retrofitting a 964 piece onto the 993 camshaft, which allows maintaining the correct position. The piece is the end piece of the camshaft on which the chain tensioner lies. The 993 part number is 901 105 546 02. The 964 part number is 901 105 546 01.
The part in blue is the part I am talking about. The 993 part looks like this:
The 964 part looks like this:
You will notice that the 964 part has more holes around the outside than the 993 counterpart. This allows inserting the pin (part 8) to set the correct camshaft position more accurately.
I am not a mechanic. I have tried to explain this the way I understood it. I had it done to my car, and I noticed the difference. They measured my openings as: 0.76mm (left cylinder bank) and 0.87mm (right cylinder bank). Now both are exactly 1mm, resulting in optimum hp.
The part in blue is the part I am talking about. The 993 part looks like this:
The 964 part looks like this:
You will notice that the 964 part has more holes around the outside than the 993 counterpart. This allows inserting the pin (part 8) to set the correct camshaft position more accurately.
I am not a mechanic. I have tried to explain this the way I understood it. I had it done to my car, and I noticed the difference. They measured my openings as: 0.76mm (left cylinder bank) and 0.87mm (right cylinder bank). Now both are exactly 1mm, resulting in optimum hp.
Last edited by 993RS; 03-22-2005 at 05:15 PM.
03-22-2005, 12:38 PM
#3
Three Wheelin'
Very interesting Phil. Thanks for those details.
I remember when you posted about this.
I just checked in the Pet, and it seems the first 993 had the 964 part until 3-95.
Here are the wheels you're talking about (pict) My car is a 96.
I remember when you posted about this.
I just checked in the Pet, and it seems the first 993 had the 964 part until 3-95.
Here are the wheels you're talking about (pict) My car is a 96.
Trending Topics
03-22-2005, 04:27 PM
#11
Race Car
Thread Starter
What I would like to make evident is that it seems to me that the cheapest way to around 20 additional hp, is to set the correct valve opening on both camshafts (and make sure that they hold their position), instead of more expensive mods! Maybe some experienced mechanics out there would care to comment? Steve?
09-20-2010, 08:01 PM
#12
Rennlist Member
Bumping a very old thread, sorry. I am getting ready to do my 120k mile service, and was going to ask the mechanic about this camshaft timing thing. I don't care about the +20hp (only because I find it too hard to believe), but I was wondering if any of you had checked into this and done anything about it, and is it worth doing? Can it even be done without dropping the engine? Thanks!
09-20-2010, 08:19 PM
#13
I've done this on my early 911 a few times and can say that while it's not difficult, it's a very tedious process with the engine on a stand. I would not want to attempt it with the engine in the car, although I'm sure it's possible.
I'd suspect that the labor to do this during your planned service would be substantial and maybe even make the "20HP" gain more expensive than other known options!
Now, when I do the top-end on my car, you can bet I'll spend the time to dial it all in perfectly as there is some satisfaction in knowing that you've got it nailed down to 0.1mm.
Now, if there is reason to believe that the time has slipped or changed, then it's certainly worth looking into since the results of poor timing are BAD.
I'd suspect that the labor to do this during your planned service would be substantial and maybe even make the "20HP" gain more expensive than other known options!
Now, when I do the top-end on my car, you can bet I'll spend the time to dial it all in perfectly as there is some satisfaction in knowing that you've got it nailed down to 0.1mm.
Now, if there is reason to believe that the time has slipped or changed, then it's certainly worth looking into since the results of poor timing are BAD.
09-20-2010, 08:37 PM
#14
Bumping a very old thread, sorry. I am getting ready to do my 120k mile service, and was going to ask the mechanic about this camshaft timing thing. I don't care about the +20hp (only because I find it too hard to believe), but I was wondering if any of you had checked into this and done anything about it, and is it worth doing? Can it even be done without dropping the engine? Thanks!
When I had my '97 3.8 rebuilt I bought cams w/ the older style cam ends and retrofitted the older sprockets
here's a pic
you will not be able to retro fit w/o new cams or machining the old ones
09-20-2010, 09:18 PM
#15
Drifting
This is an interesting topic as I contemplate upgrading my engine. I'll have to check the build date on my car but I might be lucky enough to have the earlier set-up. 
IMHO 20hp might be a worst case scenario and it would be cheap hp in this case! I suppose it depends on how much they have moved. Too much movement and hp loss will be the least of your worries and I haven't heard of this happening.
Forgive me if my Porsche engine knowledgeable is weak as my reference is American V8s when it comes to hands on work but I can see the advantage of the friction fit design. Adjustment is infinitely variable while the old one is dependent on the indexing and machining of parts. Don't assume that there is inaccuracy here either. Every part has tolerances. Even with simple V8s the cam timing is checked and special gears or offset bushings are used to make the correction. Perhaps the old design has this feature built into the sprockets. I thought the setting was 1.5 mm? Is this valve opening at a specified crank position? What does this correlate to in degrees? Surely +/-1 degree would not be noticeable.
One other thing to consider is that I'd sure want to establish that the engine is down on power before spending the $$$. It might be worthwhile checking the timing when the engine is out especially if you are doing a reseal anyway.
Perhaps I'm sick but I'm looking forward to the day when I can get my engine out and into bits.
IMHO 20hp might be a worst case scenario and it would be cheap hp in this case! I suppose it depends on how much they have moved. Too much movement and hp loss will be the least of your worries and I haven't heard of this happening. Forgive me if my Porsche engine knowledgeable is weak as my reference is American V8s when it comes to hands on work but I can see the advantage of the friction fit design. Adjustment is infinitely variable while the old one is dependent on the indexing and machining of parts. Don't assume that there is inaccuracy here either. Every part has tolerances. Even with simple V8s the cam timing is checked and special gears or offset bushings are used to make the correction. Perhaps the old design has this feature built into the sprockets. I thought the setting was 1.5 mm? Is this valve opening at a specified crank position? What does this correlate to in degrees? Surely +/-1 degree would not be noticeable.
One other thing to consider is that I'd sure want to establish that the engine is down on power before spending the $$$. It might be worthwhile checking the timing when the engine is out especially if you are doing a reseal anyway.
Perhaps I'm sick but I'm looking forward to the day when I can get my engine out and into bits.