Thread: 355 cam choice

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Originally Posted by techinspector1

SBC has asked a question on PM about the cam we used above and the calculator on the Keith Black Pistons site. My answer is way too long for the PM, so I will publish it here on the board.




There is duration at 0.050" tappet lift and there is duration at seat-to-seat (On a hydraulic cam, usually shown as 0.006" tappet lift. On a solid cam, usually shown as 0.020" tappet lift. This is also shown as "advertised" duration.)

Let's say a theoretical cam has a duration @0.050" of 230 degrees. Let's further say that at 0.006", the duration is 200 degrees. (The difference used here is too radical to be a real-world cam, but I just need to do it this way to explain the calculator). We have 30 degrees of difference between 0.050" and advertised duration on the lobes of this cam. We are dealing with the intake lobe for use in the calculator. So, the lobe would have a difference of 15 degrees on the opening ramp and 15 degrees on the closing ramp of the same intake lobe. So the calculator is asking you to add 15 degrees to the 0.050" closing point that you have to enter into the calculator in order to get the valve closer to its seat position. As you know, we cannot begin compression in the cylinder until we close the intake valve. That's just the way the calculator is configured and something we have to work with to use the calculator.

Hi tech, thanks for the links to UDHarolds post. He is a wealth of knowlege. There is a small typo in your post above you may wish to change to avoid confusion, no disrespect intended.

Cheers

Originally Posted by Rimmo

Hi tech, thanks for the links to UDHarolds post. He is a wealth of knowlege. There is a small typo in your post above you may wish to change to avoid confusion, no disrespect intended.
Cheers

Thank you. I swapped the 200 and 230. Now it makes sense....I think