Finding Cam Intake Duration from a known IVC

[Frank]

This is not "hardcore tech", but I've found it helpful.
When using a compression calculator to plan a build and all the volume variables are plugged in, enter an IVC number that gives the desired DCR, then calculate the cam overlap needed to attain that IVC using this:
Duration=2(IVC+180-LSA)
I find this quicker than guessing a cam that's close and plugging it into the calculator searching for the exact DCR.

 

[pmuller9]

In most cases for a street cam, the cam card specifies a 4 degree advance which is LSA - 4.

The re-write would be Duration=2(IVC+176-LSA)

 

[Frank]

In most cases for a street cam, the cam card specifies a 4 degree advance which is LSA - 4.

The re-write would be Duration=2(IVC+176-LSA)

Yes sir, I realized I had omitted the advance, or retard. Since the formula is working in reverse- we know desired IVC, and are searching for the necessary duration, then the advance has to be added to the sum after it's calculated to arrive at the correct IV duration.
2(IVC+180-LSA) + *advance. The advance is a direct degree change, and can't be computed into the brackets.
Example: desired IVC= 64*, 110* LSA:
2(64+180-110)= 268* IV duration straight up.
2(64+176-110)=260* X
2(64+184-110)=276* X
2(64+180-110)=268*+4* advance=272* IV duration @ 4* advanced for IVC of 64*