Mgardiner1 wrote:I really feel like i'm being an a-hole....... But the 2 methods of finding DCR do not work together. A manufacturers spec for IVC includes the amount of timing already built into the cam. If you don't know the IVC and use the duration and LSA, it figures the DCR using 0 degrees advanced.

Going back to the mopar 30AB cam entering the following data: 260 duration, 108 LSA, and 0 adv/ret gives a DCR of 8.08 with the numbers i am using. If i use the same number, but check the box for IVC and enter in 54 (Supplied by dwg86 and reed cams) with a 0 adv/ret i get 8.28.

260/108/0 = 8.08

260/108/+4 = 8.28

So mopar's spec for IVC is 4 deg advanced that is built into the cam (meaning if you set your timing marks at 0, the cam is advanced 4 deg BY DESIGN). Of course, retarding it 4 degrees would make a 0 spec.

IVC i think is really the only true way to know what the DCR is. Duration and LSA are required to find IVC, but don't you also need Intake Center Line to find the IVC?

So your saying it was a mistake for us to have the calculator use advance / retard when its only given a IVC angle? Or are you saying the math is wrong?

Here is what i get using your numbers..

First of all here is how you calculate IVC from LSA and Duration:

First our Givens:

Code: Select all

```
duration1=duration/2
IVCA1=lsa-advance
```

Now to the actual math:

Now if i use your numbers:

duration1=130

IVCA1=108

Now:

IVCA=130-(180-108)

or

IVCA=58

So your right there is 4 degrees of crankshaft advance built into their IVC spec... So that tells me that when using LSA and duration, you need to punch in 4 for advance....

You can see by the math above that the numbers are punching correctly... so it seems to me that the figures that you were given do not include the 4 degrees of advance when the IVC spec you were given does.

Does that make since?

So basically is seems when using IVCA, the advance / retard feature of the calculator should not include the actual cam advance.... only the amount of manual advance or retard they plan to use right?

Lets look at the specs below:

Duration=260

LSA=108

Advance=4

IVCA=54

When using Duration and LSA, we would punch in 4 degrees advance.

When using IVCA we would leave the advance field blank. (Because apparently IVCA includes the amount of advance).

Now when cam manufactures give IVCA, does that spec ALWAYS include advance / retard? If so then what i stated above is true. If not, then we have an entirely new problem that could never be resolved.

Am i following so far, or am i way off base?

Also, please dont feel like your being an asshole... the more feedback we get on the calculator, the more accurate it will be.