Please help me find my missing HP.
08-18-2008, 11:20 PM
#106
Former Sponsor
I just opened Rennlist for the first time in months and found this discussion. I've tried to read through this stuff, but I'm seriously confused.....which doesn't take much.
When I say Mark....I mean Mark Anderson. I have no clue what Mark K. is doing...I'm trying to understand exactly how he is checking his cams. The first 20 times I read the workshop manual, I had absolutely no clue what they were doing, or why. I seriously thought that they had failed to translate the information to English! Once you actually do it a few times and do some "translation" on your own, it actually starts to make sense. Since all the measuring is done by turning the crankshaft and measuring the actual camshaft opening in relationship to the crankshaft, it is difficult to see how this process could be wrong. For some reason, Porsche chose to give all the cam specification in the WSM in opening and closing degrees. It only takes a few moments to convert this information to lobe center information....and them it really gets clear what Porsche was doing with the different engines. It also makes checking camshaft timing a cinch, with a degree wheel.
I started to get into this, in the past, but I think most got lost pretty quickly. It turns out the the cam differences between engines are substancial. Forget lift and duration. Look at what they did with lobe centers and the differences in engines and how they act is instantly obvious.
Since cam timing is totally dependant upon crank position, it would seem that anything that changes the relationship of the distance from the crankshaft to the camshaft would effect any method of measuring the cam timing that was not taken directly from the crankshaft. As I said, I have no idea how Ken's cam timing tool works and how actual crank degrees are measured when the cam timing is being checked. I'm trying to understand.
When I say Mark....I mean Mark Anderson. I have no clue what Mark K. is doing...I'm trying to understand exactly how he is checking his cams. The first 20 times I read the workshop manual, I had absolutely no clue what they were doing, or why. I seriously thought that they had failed to translate the information to English! Once you actually do it a few times and do some "translation" on your own, it actually starts to make sense. Since all the measuring is done by turning the crankshaft and measuring the actual camshaft opening in relationship to the crankshaft, it is difficult to see how this process could be wrong. For some reason, Porsche chose to give all the cam specification in the WSM in opening and closing degrees. It only takes a few moments to convert this information to lobe center information....and them it really gets clear what Porsche was doing with the different engines. It also makes checking camshaft timing a cinch, with a degree wheel.
I started to get into this, in the past, but I think most got lost pretty quickly. It turns out the the cam differences between engines are substancial. Forget lift and duration. Look at what they did with lobe centers and the differences in engines and how they act is instantly obvious.
Since cam timing is totally dependant upon crank position, it would seem that anything that changes the relationship of the distance from the crankshaft to the camshaft would effect any method of measuring the cam timing that was not taken directly from the crankshaft. As I said, I have no idea how Ken's cam timing tool works and how actual crank degrees are measured when the cam timing is being checked. I'm trying to understand.
08-18-2008, 11:34 PM
#107
Former Sponsor
BTW...I went over with Mark Anderson to his dyno session, this afternoon. The output readings (from the dyno) are exactly the same with and without the knock sensors hooked up. It would seem, to me, that this might be the source of the problem with Mark's power output.
Anyway, that is where I intend to start, tomorrow.
As I said, I check cam timing from lobe centers, with a degree wheel. I check both the intake cams and the exhaust cams....to make sure that everything is working at the correct time. I do this while I'm setting the cams and when I'm done and everything is torqued and I'm ready to install the front covers. I also check opening and closing events (on both intake and exhaust), just to make sure things are happening correctly. The results are recorded in the engine building data sheets.
There is absolutely no chance that Mark Anderson's cam timing is off by 1 degree from where I intended it to be. I will not even bother double checking it. It has already been double and triple checked.
Anyway, that is where I intend to start, tomorrow.
As I said, I check cam timing from lobe centers, with a degree wheel. I check both the intake cams and the exhaust cams....to make sure that everything is working at the correct time. I do this while I'm setting the cams and when I'm done and everything is torqued and I'm ready to install the front covers. I also check opening and closing events (on both intake and exhaust), just to make sure things are happening correctly. The results are recorded in the engine building data sheets.
There is absolutely no chance that Mark Anderson's cam timing is off by 1 degree from where I intended it to be. I will not even bother double checking it. It has already been double and triple checked.
08-18-2008, 11:57 PM
#108
Under the Lift
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Wow
I use lobe centers to set and check cams....which is the most correct way to check a camshaft.
Non stock camshafts require serious thinking. It becomes important to know which cores the cams are made from. Most cam grinders can't changed the lobe location, so the lobe centers will always remain the same.
I use lobe centers to set and check cams....which is the most correct way to check a camshaft.
Non stock camshafts require serious thinking. It becomes important to know which cores the cams are made from. Most cam grinders can't changed the lobe location, so the lobe centers will always remain the same.
As I said, I check cam timing from lobe centers, with a degree wheel. I check both the intake cams and the exhaust cams....to make sure that everything is working at the correct time.
The first 20 times I read the workshop manual, I had absolutely no clue what they were doing, or why. I seriously thought that they had failed to translate the information to English! ... It only takes a few moments to convert this information to lobe center information....and them it really gets clear what Porsche was doing with the different engines. It also makes checking camshaft timing a cinch, with a degree wheel.
Forget lift and duration. Look at what they did with lobe centers and the differences in engines and how they act is instantly obvious.
Forget lift and duration. Look at what they did with lobe centers and the differences in engines and how they act is instantly obvious.
We certainly agree on this!
08-18-2008, 11:59 PM
#109
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Mark said the knock sensors checked out OK. I assume the Hall sensor as well. If not, then this would explain the loss at high RPM.
08-19-2008, 12:52 AM
#110
Inventor
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IIRC, this rebuild was for changing rods, and rod bearings, only, were the cams set via the lobe centers for this rebuild?
I do not have a clue how Ken's tool works (I've never seen one), but I'm assumming that his tool works off of the key groove cut into the camshaft and that he checked all the different 928 camshafts and found that all key grooves were cut to some "exact standard". This, if true, would enable him to make a tool that indexes off of the camshaft key grooves and get a reliable method of setting cam timing.
If this is all true, Ken's tool should work reliably, as long as everything is stock.
As soon as camshafts get modified, one can no longer use the stock Porsche method used in the workshop manual. Any change in the shape of the lobe will render this method invalid.
Non stock camshafts require serious thinking. It becomes important to know which cores the cams are made from. Most cam grinders can't changed the lobe location, so the lobe centers will always remain the same. So, a cam made from a GT core will be radically different than a cam made from a S-4 core, even though the lobes may be the exact same shape.
If this is all true, Ken's tool should work reliably, as long as everything is stock.
As soon as camshafts get modified, one can no longer use the stock Porsche method used in the workshop manual. Any change in the shape of the lobe will render this method invalid.
Non stock camshafts require serious thinking. It becomes important to know which cores the cams are made from. Most cam grinders can't changed the lobe location, so the lobe centers will always remain the same. So, a cam made from a GT core will be radically different than a cam made from a S-4 core, even though the lobes may be the exact same shape.
The current version, V2, is advanced by 2°, to match the empirically determined zero. It has laser cut holes which are spaced 1° apart.
With non-stock cams, you set the cams first using the lobe centers, then record the degree measurement the 32V'r shows. From that point on, you can use the 32V'r to go adjust plus or minus, or even replace a cam gear.
Last edited by PorKen; 08-19-2008 at 01:08 AM.
08-19-2008, 12:55 AM
#111
Administrator - "Tyson"
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08-19-2008, 01:00 AM
#112
Former Sponsor
Yes, this disassembly and reassembly was an exercise to change the rods to a different design. I did reset the cams using lobe centers. I didn't even bother to mark them when I disassembled the engine, since I always set them starting from scratch.
Sounds like I need to get one of your tools. This would make changing cam gears, when doing a cam belt, much easier. Please send me information.
thanx,
Sounds like I need to get one of your tools. This would make changing cam gears, when doing a cam belt, much easier. Please send me information.
thanx,
08-19-2008, 01:06 AM
#113
Inventor
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Since cam timing is totally dependant upon crank position, it would seem that anything that changes the relationship of the distance from the crankshaft to the camshaft would effect any method of measuring the cam timing that was not taken directly from the crankshaft. As I said, I have no idea how Ken's cam timing tool works and how actual crank degrees are measured when the cam timing is being checked. I'm trying to understand.
It dawned on me that once you have a tool like mine, which measures the angle of the exhaust cam to a fixed point on the head, the crank/cam centers, even the belt length no longer matter. As long as you do not change the angle of the head somehow, the tool will always show the correct degree value. Just like the water pump pointer always shows the location of TDC on the balancer.
You do have to adjust the cam using the tool to match the crank TDC, but engine to engine, the tool will always measure the correct degree, and this has proven to be the case.
08-19-2008, 01:18 AM
#114
Inventor
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Yes, this disassembly and reassembly was an exercise to change the rods to a different design. I did reset the cams using lobe centers. I didn't even bother to mark them when I disassembled the engine, since I always set them starting from scratch.
Sounds like I need to get one of your tools. This would make changing cam gears, when doing a cam belt, much easier.
Sounds like I need to get one of your tools. This would make changing cam gears, when doing a cam belt, much easier.
If you go (here), there is more info on the 32V'r, and the occasionally updated (PDF manual). Roger of (928sRUs), stocks them.
I'm proud to say that quite a few tuners/mechanics have bought the tool, and have been happy with the time savings it affords.
08-19-2008, 02:01 AM
#115
Former Sponsor
Ken:
If all stock camshafts are indexed to the same place, in terms of lobe center to the cam key, your tool has to work. It never occurred to me that Porsche might have ground all the cams from the same index point, especially from year model to year model. It sounds like you measured a bunch of camshaft lobe centers (from different years) and determined that this is true, from your description. When I stop and think about this, it all makes sense, otherwise it would be very difficult for Porsche to tell the cam maker what to change from model to model.
Porsche sure made the cam timing process overly complex, if this is the case. That is really strange, since Porsche tends to not hesitate to make expensive special tools to do relatively simple tasks.
The ability to check and set stock cam timing without removing the valve cover is worth a bunch of money, even if you only use the tool once and throw it away when you are done! I understand your point about doing lobe centers once on a non stock application and then measuring and recording the results with your tool. That should save literally hours of measuring and seting cam timing. I just spent 4-5 hours of setting and checking on Mark Anderson's engine alone!
I'm feeling kind of stupid....again. Stupid for not having one of these tools!
If all stock camshafts are indexed to the same place, in terms of lobe center to the cam key, your tool has to work. It never occurred to me that Porsche might have ground all the cams from the same index point, especially from year model to year model. It sounds like you measured a bunch of camshaft lobe centers (from different years) and determined that this is true, from your description. When I stop and think about this, it all makes sense, otherwise it would be very difficult for Porsche to tell the cam maker what to change from model to model.
Porsche sure made the cam timing process overly complex, if this is the case. That is really strange, since Porsche tends to not hesitate to make expensive special tools to do relatively simple tasks.
The ability to check and set stock cam timing without removing the valve cover is worth a bunch of money, even if you only use the tool once and throw it away when you are done! I understand your point about doing lobe centers once on a non stock application and then measuring and recording the results with your tool. That should save literally hours of measuring and seting cam timing. I just spent 4-5 hours of setting and checking on Mark Anderson's engine alone!
I'm feeling kind of stupid....again. Stupid for not having one of these tools!
08-19-2008, 02:12 AM
#116
Former Sponsor
Bill:
I tried to "look" at the knock sensors using the Sharktuner, while the car was on the dyno. As soon as we started the engine, the "monitoring" part of the sharktuner went nuts....as well as the recording part of the Sharktuner. All was fine, with the engine off and just sitting there. All was fine, with the key turned on. It all turned bad when the engine actually was running. I assume that is was caused by some sort of interference between the open EZK unit and the engine. However, this might be a "real" thing that is going on and causing the knock sensors to not work. The other interesting thing, about this, is that the engine sounded and ran the same, with the box open and the Sharktuner hooked up.
I'll dig in tomorrow.
I tried to "look" at the knock sensors using the Sharktuner, while the car was on the dyno. As soon as we started the engine, the "monitoring" part of the sharktuner went nuts....as well as the recording part of the Sharktuner. All was fine, with the engine off and just sitting there. All was fine, with the key turned on. It all turned bad when the engine actually was running. I assume that is was caused by some sort of interference between the open EZK unit and the engine. However, this might be a "real" thing that is going on and causing the knock sensors to not work. The other interesting thing, about this, is that the engine sounded and ran the same, with the box open and the Sharktuner hooked up.
I'll dig in tomorrow.
08-19-2008, 02:30 AM
#117
928 Collector
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Agreed ... just get one Greg. EVEN I CAN SET TIMING NOW....
08-19-2008, 02:42 AM
#118
Rennlist Member
Greg, If you didnt muddle you way through some of my posts, in a nutshell, i used the workshop manual technique to set the cams. after they were done, I was done. a friend who regularly does this kind of work in building BMW race engines, verified the little distance the lifter moves when the crank is moved 20 degrees advanced. i set both sides at 2mm, because the Holbert car was disasembled and found this way, and it seemed to make the power it should.
when i used the porken tool, it told me that i was off 6 degrees advanced on the driver exhaust cam and 3 degrees on the passenger exhuast cam. the intake lifter depression was dead nuts on , but why was the tool telling me otherwise? Ken came up with some reasons, chain slack, head shaved, block shaved, I used the gauge incorrectly, etc. All of which could be the issue.
I can tell you I checked the WSM setting many times and we did it with the dial indicator 5 times all showing a .078" depression (2mm)
anyway, it seems there is a flaw in using the tool in all situations. it seems that on a stock set up with stock parts, it works very well. Im thinking its a great idea for a realitive change of parts and reassembly of your old stuff.
Lots of advantages, but i want to understand why the discrepancy with my set up. the cams even were 113mm apart based on that little raised boss pointer on both cams.
Andersons cams are fine, im sure its something to do with the knock sensors or ECU. You guys will fix it!
mk
when i used the porken tool, it told me that i was off 6 degrees advanced on the driver exhaust cam and 3 degrees on the passenger exhuast cam. the intake lifter depression was dead nuts on , but why was the tool telling me otherwise? Ken came up with some reasons, chain slack, head shaved, block shaved, I used the gauge incorrectly, etc. All of which could be the issue.
I can tell you I checked the WSM setting many times and we did it with the dial indicator 5 times all showing a .078" depression (2mm)
anyway, it seems there is a flaw in using the tool in all situations. it seems that on a stock set up with stock parts, it works very well. Im thinking its a great idea for a realitive change of parts and reassembly of your old stuff.
Lots of advantages, but i want to understand why the discrepancy with my set up. the cams even were 113mm apart based on that little raised boss pointer on both cams.
Andersons cams are fine, im sure its something to do with the knock sensors or ECU. You guys will fix it!
mk
Ken:
If all stock camshafts are indexed to the same place, in terms of lobe center to the cam key, your tool has to work. It never occurred to me that Porsche might have ground all the cams from the same index point, especially from year model to year model. It sounds like you measured a bunch of camshaft lobe centers (from different years) and determined that this is true, from your description. When I stop and think about this, it all makes sense, otherwise it would be very difficult for Porsche to tell the cam maker what to change from model to model.
Porsche sure made the cam timing process overly complex, if this is the case. That is really strange, since Porsche tends to not hesitate to make expensive special tools to do relatively simple tasks.
The ability to check and set stock cam timing without removing the valve cover is worth a bunch of money, even if you only use the tool once and throw it away when you are done! I understand your point about doing lobe centers once on a non stock application and then measuring and recording the results with your tool. That should save literally hours of measuring and seting cam timing. I just spent 4-5 hours of setting and checking on Mark Anderson's engine alone!
I'm feeling kind of stupid....again. Stupid for not having one of these tools!
If all stock camshafts are indexed to the same place, in terms of lobe center to the cam key, your tool has to work. It never occurred to me that Porsche might have ground all the cams from the same index point, especially from year model to year model. It sounds like you measured a bunch of camshaft lobe centers (from different years) and determined that this is true, from your description. When I stop and think about this, it all makes sense, otherwise it would be very difficult for Porsche to tell the cam maker what to change from model to model.
Porsche sure made the cam timing process overly complex, if this is the case. That is really strange, since Porsche tends to not hesitate to make expensive special tools to do relatively simple tasks.
The ability to check and set stock cam timing without removing the valve cover is worth a bunch of money, even if you only use the tool once and throw it away when you are done! I understand your point about doing lobe centers once on a non stock application and then measuring and recording the results with your tool. That should save literally hours of measuring and seting cam timing. I just spent 4-5 hours of setting and checking on Mark Anderson's engine alone!
I'm feeling kind of stupid....again. Stupid for not having one of these tools!
08-19-2008, 02:28 PM
#119
Former Sponsor
Mark K:
I would guess that the confusion, in your camshaft setting proceedure, probably is coming from the difference in camshafts. I'm guessing that the Holbert car had GT cams. Their factory setting point should have been 2.8mm for the 1-4 side and 3.1mm for the 5-8 side. This would have resulted in an intake lobe center of 112.5 degrees and an intake lobe center of 107.5 degrees. As the belt streatched, the cam timing would naturally retard towards 110 degree lobe centers, which is probably what the factory was shooting for. It would seem natural for the factory to set a special engine at 110 degree lobe centers, from the start. This would continue to retard, as the belt wore, and you could easily end up with your measured 2.0mm, in time.
The '85/'86 camshafts are set originally at 1.6mm for the 1-4 side and 2.0mm for the 5-8 side. This would result in an intake lobe center of 120.5 degrees and an exhaust lobe center of 107.5 degrees. This is a fairly "advanced" setting for these camshafts....the factory was obviously trying to get some better low end torque out of these engines and intentionally advanced the cam timing to help with this. Note that if you were to "retard" these camshafts 5 degrees, you would have an intake lobe center of 115.5 degrees and an exhaust lobe center of 112.5 degrees. Note that you can never get these cams to have 110 degree lobe centers (we're asuming that 110 degrees is optimum for this conversation), like on the GT models, but you can get pretty close by retarding the cam timing 5 degrees.
What does this mean to you? The setting that you used for the '85/'86 camshafts has advanced cam timing, relative to the GT cams. This will give you better low end and better throttle response coming out of corners. This might not be exactly what you need, since you should have tons of torque from the larger engine. A retarted position would cut a bit from the low end torque, but improve the higher rpm potential of the engine. While I would have to measure and degree a set of '85/'86 camshafts to be sure, I'd guess that you might like the engine better, if you were to retard them a bit....the "next" time you are in there. I'd guess that a setting of 1.2mm on the 1-4 side and 1.6mm on the 5-8 side (with a new FACTORY timing belt) might be closer to what you need. If the belt is already streatched FACTORY belt (used) you might want to advance that number a few degrees. If you are running one of the "streatchy" aftermarket belts.....well good luck trying to figure out what happens at the camshafts.....all bets are off.
I would guess that the confusion, in your camshaft setting proceedure, probably is coming from the difference in camshafts. I'm guessing that the Holbert car had GT cams. Their factory setting point should have been 2.8mm for the 1-4 side and 3.1mm for the 5-8 side. This would have resulted in an intake lobe center of 112.5 degrees and an intake lobe center of 107.5 degrees. As the belt streatched, the cam timing would naturally retard towards 110 degree lobe centers, which is probably what the factory was shooting for. It would seem natural for the factory to set a special engine at 110 degree lobe centers, from the start. This would continue to retard, as the belt wore, and you could easily end up with your measured 2.0mm, in time.
The '85/'86 camshafts are set originally at 1.6mm for the 1-4 side and 2.0mm for the 5-8 side. This would result in an intake lobe center of 120.5 degrees and an exhaust lobe center of 107.5 degrees. This is a fairly "advanced" setting for these camshafts....the factory was obviously trying to get some better low end torque out of these engines and intentionally advanced the cam timing to help with this. Note that if you were to "retard" these camshafts 5 degrees, you would have an intake lobe center of 115.5 degrees and an exhaust lobe center of 112.5 degrees. Note that you can never get these cams to have 110 degree lobe centers (we're asuming that 110 degrees is optimum for this conversation), like on the GT models, but you can get pretty close by retarding the cam timing 5 degrees.
What does this mean to you? The setting that you used for the '85/'86 camshafts has advanced cam timing, relative to the GT cams. This will give you better low end and better throttle response coming out of corners. This might not be exactly what you need, since you should have tons of torque from the larger engine. A retarted position would cut a bit from the low end torque, but improve the higher rpm potential of the engine. While I would have to measure and degree a set of '85/'86 camshafts to be sure, I'd guess that you might like the engine better, if you were to retard them a bit....the "next" time you are in there. I'd guess that a setting of 1.2mm on the 1-4 side and 1.6mm on the 5-8 side (with a new FACTORY timing belt) might be closer to what you need. If the belt is already streatched FACTORY belt (used) you might want to advance that number a few degrees. If you are running one of the "streatchy" aftermarket belts.....well good luck trying to figure out what happens at the camshafts.....all bets are off.
08-19-2008, 03:07 PM
#120
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Mark: Greg has been kind enough to take the time to try to sort through the variables in your cam timing in the post above. Very nicely done. Note that Greg forgoes the WSM technique and uses lobe centers, which is how Jim Morton had us time Dennis' cams. Had we not changed out his chain and tensioner pads, we would have had 3° error in angle between the intake and exhaust cams. You can speculate as to why Porsche chose to use lift at 20° ATDC. For many people it may be easier to measure lift more accurately at that point, where the cam face is rapidly accelerating, than at the lobe center, where the dwell at the top of the lobe requires some care to get accurately, just like piston TDC.
Last edited by Bill Ball; 08-19-2008 at 09:47 PM.