What's your favorite DCR calculator?

[bill_396]

Searching on line I see a lot of variations on DCR calculators, any consensus on which one to use? Have been using the KB/Silvolite one because I had trouble getting the Pat Kelly one working. I have the Kelly one going now and it looks like I may not have been getting the best answers from the Silvolite one. Appears the intake closing point calc is a little suspect there. thanks

[jayb]

http://www.empirenet.com/pkelley2/DynamicCR.html

[My427stang]

Same here, I've done so many now using that one that I trust the results

[chilly460]

Very nice, never done this before.  I had to guesstimate a couple items on my 390 as it's been so long since I was in the engine, or plain don't have some info, but came up with 8.011 DCR.

[TorinoBP88]

You have to remember to hit inches as it defaults to metric.

[KMcCullah]

http://www.empirenet.com/pkelley2/DynamicCR.html

Wow! So much explained in one link. Good info!

[fairlaniac]

An interesting topic that I never knew much about. So now I'm trying to learn and understand it all.

So I'm gathering parts to bulid a 427 (484) using a scat 4.25 crank, 6.700 rods and this cam.
I used 72cc on the head as a hypothetical number. I don't have heads yet.

So here are some of the numbers I figured from PKelley's link above.

RD - 1.674523
ICA - 52
RR - 1.308
RL - 6.700
PR1 - 6.487376
PR2 - 5.179095
ST - 4.25
1/2ST - 2.125
DST - 3.645905

I'll assume my numbers are correct, now I'm not sure what to do with the DST number. I tried the program on the website to figure DCR but it didn't seem right. I guess if I have a question, did I do my math correctly and now what do I do with my new found information.

Thanks,

[ScotiaFE]

You can just plug the numbers into his calculator.
You have to download it.
It's the link at the bottom of the page.

I came up with a DCR of 8.578 to 1 and a DSL of 3.23.
That's using my 482 specs with a 10.96 to 1 SCR.
I think I'm using correctly.

[jayb]

An interesting topic that I never knew much about. So now I'm trying to learn and understand it all.

So I'm gathering parts to bulid a 427 (484) using a scat 4.25 crank, 6.700 rods and this cam.
I used 72cc on the head as a hypothetical number. I don't have heads yet.

So here are some of the numbers I figured from PKelley's link above.

RD - 1.674523
ICA - 52
RR - 1.308
RL - 6.700
PR1 - 6.487376
PR2 - 5.179095
ST - 4.25
1/2ST - 2.125
DST - 3.645905

I'll assume my numbers are correct, now I'm not sure what to do with the DST number. I tried the program on the website to figure DCR but it didn't seem right. I guess if I have a question, did I do my math correctly and now what do I do with my new found information.

Thanks,

Your ICA number is not correct.  The ICA number is calculated from the advertised duration, not the duration at .050".  When the lobe lift is at .050", the intake valve is still open.  You want the ICA angle to be when the intake valve has just closed, not when it is still hanging open. 

Looking at your card, the duration at .020" tappet lift is 287.  Given lash of .020", this is exactly when the intake valve has closed.  Using 287 for the intake duration, the ICA will be 67.5, assuming you have degreed the cam according to the card, at an intake lobe centerline of 104 degrees.

Try 67.5 for the ICA and see if you get a more reasonable number.

>>>Edit:  Thinking about this, I goofed on one of my previous statements.  .020" tappet lift is NOT exactly when the intake valve has closed.  At .020" tappet lift, you have valve lift of about .035" due to the rocker ratio.  Subtracting .016" from this for lash (according to the lash specs on the cam card), you will still have the intake valve open .020" at this point.  So for seat to seat intake duration, you would want the measurement at about .010" tappet lift, which is about .017" valve lift after accounting for rocker ratio, and about 0 valve lift when lash is subtracted.

You could probably use the .020" tappet duration anyway and get a good DCR number, but I think I would add a little to the duration to be safe.  So, instead of 287, maybe use 292.  This would make your ICA number 70.

Hope that helps - Jay

[fairlaniac]

Jay,
Thanks! I'm still trying to identify where the new number of 70 came from? I'll see how the math works out.

[afret]

Since Jay is using 292* as the advertised duration instead of 287, you subtract the .05 duration number from that.  292-256=36.  Then divide 36 by 2 which is 18.  Add 18 to the .05 intake valve closing number of 52 and get 70.  Maybe all this isn't an exact science but should get you in the ballpark.

(I plugged 67.5 and 70 intake closing point in a simple DCR calculator using a 482 with 11.3 static compression and the DCR changed only about 0.17).