Power Valve Selection

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Bewy said:
Degreeing at 0.006" tappet lift is veeeeeeeeeeery unreliable because you are on the clearance ramps of the lobe, where you get a lot of movement [ rotation ] for a few degrees. This is why the 050 numbers are provided because you are on the flanks of the lobe & it is more accurate.
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Where are you seeing the .050" numbers on this cam card? I am only seeing the duration specified at those heights, not where the opening and closing .050" are in relation to degrees.
 
carfreak6970 said:
Where are you seeing the .050" numbers on this cam card? I am only seeing the duration specified at those heights, not where the opening and closing .050" are in relation to degrees.
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That’s why you need to degree the cam to the intake centerline. They didn’t give you the .050 lift timing numbers.
 
Hysteric said:
Do you have the list number from the choke horn? .
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sorry this is late, but I just checked and the numbers look like 80459-1

Newbomb Turk said:
That’s why you need to degree the cam to the intake centerline. They didn’t give you the .050 lift timing numbers.
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So thank you for this... I did some research and figured out how to do this method. I redid the degree checking on the initial set up and the centerline was at 122 degrees... that is 16 degrees off!! talk about terrible! so I put in the new adjustable timing set at 8R and the centerline was now at 115. Better, but not where it should be. I installed the timing set straight up (0 to 0) and it is now at 106 degrees. perfect.

Now I will post a photo later to show the issue more clearly, but is there a special washer for the cam bolt? The front face of the cam gear is a little higher off of the surface that the bolt threads into on the cam shaft. With how it sits now, it appears there will be an air gap between the cam gear and cam face which could affect the clamping force of that bolted connection. the old washer that was on there was deflected when it was torqued last, which doesn't seem like that is how it is suppose to be.


IMG_3057.jpeg
 
Using the 0.006" timing numbers will give veeeeery inaccurate results......as you are finding out. That is because the 006 includes the opening & closing ramps which are often different [ asymmetric lobe design, very common today ]. The closing ramp is often slightly longer [ more degrees of rotation ] to seat the valve more gently. Starting at the max lobe lift point, there are more degrees on the closing side than on the opening side. Hence the strange numbers you are getting. The opening/closing ramps are out of the picture at 050 lobe lift, which is why this is used for checking/centerling. I would contact Comp & get the 050 numbers & then you will get accurate results.
 
Using the centerline method I got the cam shaft degreed in properly. I believe I got the intake vacuum leak issue nipped in the butt and was able to not only start the car but did drive it into storage before the snow came. It appears I need to have the choke come off sooner, so I will work on that come spring. but with the timing set and the idle stuff readjusted on the car I believe it ran really well. idle in neutral is about 12-13 inHg, which is about 1-2" better than before. So on the right track. There is now no stumble off of idle, which is good. But it is tucked away for winter so I wont be able to dive into the carb until the roads clear.
 
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