Okay. How do I time these cams (cam card info)
02-09-2010, 04:07 PM
#31
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One other possibility is that the intake number is just the stock intake cam info, not the reground exhaust info. IIRC, 10mm lift and 255° duration is pretty much exactly what a stock S3 intake is. I guess the intake lobe pattern could be ground on the exhausts but after seeing the rest of that info, I'd want to double check.
If you're looking at the factory manuals, they show a raised pointer to guide you in locating the cam on the right chain link so you have the correct timing between intake & exhaust. One S3 intake we had did not have this pointer. Another had a weird cut-off pyramid shape. This makes life more difficult.
Some numbers to keep in mind while you're timing these cams.
S3 intake factory centerline is 120.5° ATDC.
S3 exhaust factory exhaust centerline is 107.5° BTDC.
Firing order is 1-3-7-2-6-5-4-8.
Cylinder 5 fires 450° after Cylinder 1.
Passenger side cams brush down against the lifters
Driver side cams brush up against the lifters
Double check this info as it's off the top of my head. The above may seem super basic, but I get confused as hell when I'm staring at the cams in the head, trying to sort things out.
02-09-2010, 04:21 PM
#32
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Thread Starter
Dennis - the cams were ground properly - the cam card info above is referenced wrong, but the lobe measurements should be correct. IDK. But the reference issue is just from an operator who did the input wrong. This is not the sheet from the grinder:
THAT WOULD HAVE BEEN NICE TO HAVE!
THAT WOULD HAVE BEEN NICE TO HAVE!
02-09-2010, 04:30 PM
#34
Three Wheelin'
The BIG question with custom 928 32v cams is the relationship between exhaust and intake. How did they determine that for the "cam card"? Did they assume based on factory measurements? I would guess they shifted the cams on the machine so that the grinding wheel would hit on the existing lobe evenly thereby giving you the stock lobe seperation, no?.
You get to find this out in addition to the normal work!
You get to find this out in addition to the normal work!
02-09-2010, 04:36 PM
#35
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No. The increase in lift was determined by myself and others as something that could be contained by the lifter itself.
The intake max lift is 417 and the exhaust is 379.5 or so. That does not go past the stock lifter's 2mm play.
Basically, they are quite similar to the cams in your engine.
The intake max lift is 417 and the exhaust is 379.5 or so. That does not go past the stock lifter's 2mm play.
Basically, they are quite similar to the cams in your engine.
02-09-2010, 04:41 PM
#36
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Thread Starter
The BIG question with custom 928 32v cams is the relationship between exhaust and intake. How did they determine that for the "cam card"? Did they assume based on factory measurements? I would guess they shifted the cams on the machine so that the grinding wheel would hit on the existing lobe evenly thereby giving you the stock lobe seperation, no?.
You get to find this out in addition to the normal work!
You get to find this out in addition to the normal work!
The lobe separation on these are suppose to be stock, as there was no material applied to be able to change that. Only base circle reduction. Its a "cheater cam" because my high boost motor will need more lift and duration (or can take it) and I have higher compression than todd, - this cam will reduce the effective ratio a bit because of the supposed longer duration.
In Hindsight, I would have asked for more duration and lift on the exhaust cam, because of the parameters of the engine.
02-09-2010, 04:41 PM
#37
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The VarioCam was a bear... I spent hundreds of hours on cam timing.... The nice thing about the ATI Dampners are that the degree wheels bolt right to it... I used a smaller Degree wheel last time... but this next time around with my new cams I plan on getting one of the larger ones....
One of the neat tricks that I learned from Bob Norwood, was this.
Before you get the timing belt on, use the wrench boss on one of the exhaust cams, and have one loose cam journal. Place a small strip of paper on the cam journal, and tighten that cam journal when the cam is exactly where you want it. It will hold it for you. Then you can put on the timing belt sprocket, and once the belt is on and tight, you can get the timing belt gear to line up where you want it in regards to TDC on the crank. Then you remove the cap and the strip of paper, and hand crank it around.
I did both exhaust cams that way, (chain was on cam but not on the sprocket. Then I added the intake cams one at a time and went at it until it was perfect.
One of the neat tricks that I learned from Bob Norwood, was this.
Before you get the timing belt on, use the wrench boss on one of the exhaust cams, and have one loose cam journal. Place a small strip of paper on the cam journal, and tighten that cam journal when the cam is exactly where you want it. It will hold it for you. Then you can put on the timing belt sprocket, and once the belt is on and tight, you can get the timing belt gear to line up where you want it in regards to TDC on the crank. Then you remove the cap and the strip of paper, and hand crank it around.
I did both exhaust cams that way, (chain was on cam but not on the sprocket. Then I added the intake cams one at a time and went at it until it was perfect.
On the passenger side, the pad extends toward the cam cover and tightens the lobe separation, just like on a 968. On the driver's side, if you mount the tensioner to expand toward the cam cover, the lobe separation will widen. So you either have to mount Variocam assembly upside down like a standard 928 (but there doesn't seem to be room to do this) or mount it right side up and run the tensioner fully stretched at all times and when the Variocam is invoked the tensioner retracts.
Is your Variocam on the driver's side running fully extended for most of the time (wide lobe separation) and then retracts during the midrange rpm (narrow lobe separation)?
Sorry for the hijack Brendan.
02-09-2010, 04:43 PM
#38
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No Problem. This thread is only serving to confuse people because of the garbled info I posted.
02-09-2010, 04:46 PM
#39
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No. The increase in lift was determined by myself and others as something that could be contained by the lifter itself.
The intake max lift is 417 and the exhaust is 379.5 or so. That does not go past the stock lifter's 2mm play.
Basically, they are quite similar to the cams in your engine.
The intake max lift is 417 and the exhaust is 379.5 or so. That does not go past the stock lifter's 2mm play.
Basically, they are quite similar to the cams in your engine.
02-09-2010, 04:46 PM
#40
Three Wheelin'
Actually they have 3mm travel.
Not to sidetrack you but I'm a believer in running near compressed. I even do a mod to limit the travel of the lifters to .025" total and set them up by lash cap shimming. No collapsing or pump-up!
Not to sidetrack you but I'm a believer in running near compressed. I even do a mod to limit the travel of the lifters to .025" total and set them up by lash cap shimming. No collapsing or pump-up!
02-09-2010, 06:37 PM
#41
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Is that advantageous in a street engine?
02-09-2010, 07:52 PM
#42
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Thread Starter
02-09-2010, 11:22 PM
#43
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And while the conversation is going, for what I paid for these cams, plus the collar change, plus the regrind, its more expensive to do it this way that it is to buy whatever wild cam profiles that Mike Simard or Colin Jensen are doing. But they weren't doing it three years ago.
02-10-2010, 04:09 AM
#44
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Aren't the centerline measurements the max lift spec for each cam?
If the I1 cam has a lobe centerline measurement at 78.2 degrees ATDC and the E1 cam has a lobe centerline of 43.2 degrees ATDC at .050 lift would the following work as a starting point:
1) Bring #1 to TDC, zero out degree wheel;
2) With dial gauge on exhaust tappet lifter crown, turn crank (with tensioned TB) to .050 lift - note degree reading;
3) continue turning crank until tappet is fully depressed by cam lobe and starts following the closing ramp until the dial gauge again reads .050 lift - note degree reading;
4) Find the mid point degree reading between the two .050 readings, this will give you the current lobe centerline measurement for the particular cam. So if the I1 cam (assuming this is the mis-labled exhaust cam) comes in at 68 degrees ATDC, you know that it is 10.2 crank degrees advanced. Lock the cam down, retard the crank 10.2 degrees relative to the cam's locked down position, and remeasure.
As far as the intakes cams are concerned, they are pretty much just along for the ride aren't they? I mean if their lobe centers are off there isn't much that can be done to degree them in since they are driven off the exhausts and unless you have Sterlings Variocam you're kind of stuck with what you've got.
If the I1 cam has a lobe centerline measurement at 78.2 degrees ATDC and the E1 cam has a lobe centerline of 43.2 degrees ATDC at .050 lift would the following work as a starting point:
1) Bring #1 to TDC, zero out degree wheel;
2) With dial gauge on exhaust tappet lifter crown, turn crank (with tensioned TB) to .050 lift - note degree reading;
3) continue turning crank until tappet is fully depressed by cam lobe and starts following the closing ramp until the dial gauge again reads .050 lift - note degree reading;
4) Find the mid point degree reading between the two .050 readings, this will give you the current lobe centerline measurement for the particular cam. So if the I1 cam (assuming this is the mis-labled exhaust cam) comes in at 68 degrees ATDC, you know that it is 10.2 crank degrees advanced. Lock the cam down, retard the crank 10.2 degrees relative to the cam's locked down position, and remeasure.
As far as the intakes cams are concerned, they are pretty much just along for the ride aren't they? I mean if their lobe centers are off there isn't much that can be done to degree them in since they are driven off the exhausts and unless you have Sterlings Variocam you're kind of stuck with what you've got.
02-10-2010, 10:06 AM
#45
Three Wheelin'
