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Camshaft question
https://slantsix.org/forum/viewtopic.php?t=55813		 Page 3 of 3
Author:  1930 [ Wed Jul 23, 2014 3:39 am ]
Post subject: 
Hello Reed, again your e-mail was a huge help to me, it was exactly what I had been trying to find.

Another question though..........from what I have read slant cams ( and most cams nowadays ) are asymmetrical which in my understanding means one side of the lobe off centerline is fatter than another side. ( if that makes any sense )

I have read that the intake centerline method ( which is what you described in your e-mail ) is too a degree ( no pun intended ) inaccurate because trying to measure a lobe with two different lobe angles/degrees and finding equal points on their downside is nearly impossible.

So assuming what I have written is true wouldnt I want to measure at a low point on the cam for more accuracy, stick with .006 maybe? This way maybe I will be reading at points before ramps come heavily into play? I ask this because I am trying to confirm my understanding of things.

One other question, you say that your brothers van has a stock cam that is installed 8 degrees advanced, is it safe to assume that the stock hydraulic 1983 cam was cut 4 degrees advanced out of the box and you installed it an addit 4 degrees advanced as is from what I have read common for an installation where installer is going for more low end torque?

I have never read of anyone installing a cam and purposely installing it any more than 4 degrees advanced cause evidently piston to valve clearance can become an issue especially with an engine that has seen any sort of heavy machining.

Thanks
Author:  Reed [ Wed Jul 23, 2014 8:02 am ]
Post subject: 
Quote:
Hello Reed, again your e-mail was a huge help to me, it was exactly what I had been trying to find.

Another question though..........from what I have read slant cams ( and most cams nowadays ) are asymmetrical which in my understanding means one side of the lobe off centerline is fatter than another side. ( if that makes any sense )
Stock slant cams have identical intake and exhaust lobe profiles. Some aftermarket cams do not.
Quote:
I have read that the intake centerline method ( which is what you described in your e-mail ) is too a degree ( no pun intended ) inaccurate because trying to measure a lobe with two different lobe angles/degrees and finding equal points on their downside is nearly impossible.

So assuming what I have written is true wouldnt I want to measure at a low point on the cam for more accuracy, stick with .006 maybe? This way maybe I will be reading at points before ramps come heavily into play? I ask this because I am trying to confirm my understanding of things.
If the cam has different lobe profiles, instead of determining centerline by the valve overlap you determine it by measuring when the intake cam lobe reaches the highest point of lift. To do that you pick an amount of valve lift (most aftermarket cams use .050, but you could also use .006) and note when the intake lobe reaches that lift point when it opens and closes. The midpoint between those two points if the intake lobe centerline.
Quote:
One other question, you say that your brothers van has a stock cam that is installed 8 degrees advanced, is it safe to assume that the stock hydraulic 1983 cam was cut 4 degrees advanced out of the box and you installed it an addit 4 degrees advanced as is from what I have read common for an installation where installer is going for more low end torque?

I have never read of anyone installing a cam and purposely installing it any more than 4 degrees advanced cause evidently piston to valve clearance can become an issue especially with an engine that has seen any sort of heavy machining.
No, the 8 degrees of advance in my brother's van comes from a timing set that was manufactured with poor quality control and was built with the cam locating pin hole 8 degrees advanced. If I were to build the motor today, I likely wouldn't put the cam where it is. But the cam works OK for the vehicle it is in.
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