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Discussion Starter #1
I'm planning another 496 build for my chevelle. I currently have a lunati 60623 voodoo cam with specs http://www.lunatipower.com/Product.aspx?id=2185. While trying to calculate my compression ratio, I learned that the dynamic ratio matters the most on a pump gas car. When I add my specs into http://www.wallaceracing.com/dynamic-cr.php for a 496 with the 18cc domes I am considering that will gave me 10.7, I end up with a 9.55 dynamic compression. Is that too high for pump gas or too much compression for that cam or what? I'm so confused right now thanks in advance
 

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That calculator gives me 9.18 and pat kellys program gives me 9.26. I am suprised it is this high. I run 93oct pump gas. I have never had a problem keeping engine cool. I am a little worried now.
 

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I used the specs for a 496 with a 4.31 bore,4.25 stroke,6.385 rods,10.7 compression,amdc of 46.5, 400 ft elevation and it comes up with a very high 9.55 according to my research this is too much for pump gas but what really confuse me is the cam recommends 10.5 at least compression
 

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Deck height?
Head gasket?
Head cc?

Your intake closing is 72.

Your dcr is probably a little over 8. ok. L J
 

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Discussion Starter #7
Deck height?
Head gasket?
Head cc?

Your intake closing is 72.

Your dcr is probably a little over 8. ok. L J
where did you get the 72 closing point measurement from?
 

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Discussion Starter #9
Im not sure the deck measurement just estimated but I know I have a .051 head gasket and 110 cc 60459 edelbrock heads and 18cc domes probe pistons, Im still not sure how you got 72 ivc is there a formula for that, how do you calculate that? I thought you use the abdc from the cam card? Thanks for your help
 

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Brandon,my cam file program shows the seat to seat and the @.050" specs.
You can calculate it if you want -see post #13 here.
I think the cam program's easier as I write the cam file anyway and it generates the same calculations as Tim posted :yes:
 

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that formula linked above does assume a symmetrical lobe. Another easy way that provides the same result(probably all the time......havent tried the math on many cams but it worked on this one).

Advertised duration is 292. .050 duration is 241. The difference between the two = 51 degrees. Divide that in half and you get 25.5. the reason for dividing in half is because were assuming its symmetrical and were assuming 25.5 extra degrees ends up on the opening side of the lobe and 25.5 ends up on the closing side(to make up the difference from advertised and .050)

Take your intake valve closing of 46.5 at .050 and add the earlier figure we calculated of 25.5. The result equals 72. Same as the other formula, but it didnt require the ICL.

Now...72 is a lucky guess at best because Harold has mentioned numerous times his lobes arent symmetrical. That 51 degree diffrence could be spread out as 22 degrees on the opening side and 29 on the closing side(making the closing even later yet), but either way....dont calculate based on the .050 number. use advertised intake closing(which should be in the neighborhood of 72 obviously, give or take). I think you will find the numbers much more favorable, and they should be cause thats a healthy cam and should have zero problem with 10.7:1(the link to the cam card says it needs 10.5, which would be expected for a cam of those specs). You'll be good to go with those numbers.
 
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