[dougred]

Trying to figure the best cam for my combo so would like some help figuring my dynamic compression. Heres how it looks.

60 over 454 flattops, .023 deck hieght with .020 steel shim head gasket
94cc 702 big valve heads static compression of 9.7:1
Will be running 94 octane, timing advance ?
Thinking of running the Lunati Voodoo 60204

Hydraulic flat tappet
RPM Range 2,200-6,400
Intake Duration at 050 inch Lift 233
Exhaust Duration at 050 inch Lift 241
Duration at 050 inch Lift 233 int./241 exh.
Advertised Intake Duration 276
Advertised Exhaust Duration 284
Advertised Duration276 int./284 exh.
Intake Valve Lift with Factory Rocker Arm Ratio 0.554 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio 0.572 in.
Valve Lift with Factory Rocker Arm Ratio0.554 int./0.554 exh.
Lobe Separation (degrees)110

 

[Mike]

Your around 7.6 DCR
Here's an easy calculator - http://www.wallaceracing.com/dynamic-cr.php

 

[dougred]

Your around 7.6 DCR
Here's an easy calculator - http://www.wallaceracing.com/dynamic-cr.php

Would 7.6 be a little low for dynamic?

 

[Mike]

Yeah but your starting with a 9.7 static.
Doubt you'll need 94 octane.

 

[dougred]

Where in the cam specs is the intake valve closes ABDC?

 

[Mike]

http://www.lunatipower.com/CamSpecCard.aspx?partNumber=60204

It's the "In Closes 42.5 ABDC" in the above but that's @ .050" and not seat to seat.

Seat to seat is 64.0 which is what i used in the calculator and is in a cam file I wrote from the Lunati specs as they don't list seat to seat.

Here's the long version calculator that get's more precise.

 

[Highway Star]

To be real snappy, the cam needs to be smaller or on a tighter LSA to have an earlier intake closing, to build more cylinder pressure...aka dynamic compression. Even for a big block...right?

 

[71454Chevelle]

94cc 702 big valve heads static compression of 9.7:1

Did you actually measure the chambers at 94cc? That sounds small unless those heads have been milled alot.

 

[dougred]

Thanks for the help Mike. I keep getting a dynamic of 8.88:1. What am I doing wrong? Here are my inputs,

#of cyl - 8
bore - 4.310
stroke - 4
rod length - 6.135
static comp - 9.7
abdc - 42.5
boost press. -
target altitude - 100

Static compression ratio of 9.7:1.
Effective stroke is 3.63 inches.
Your dynamic compression ratio is 8.88:1 .
Your dynamic cranking pressure is 181.89 PSI.
Your dynamic boost compression ratio, reflecting static c.r., cam timing, altitude, and boost of PSI is 8.88 :1.
V/P (Volume to Pressure Index) is 231

 

[dougred]

Did you actually measure the chambers at 94cc? That sounds small unless those heads have been milled alot.

Yes they have been milled.

 

[dougred]

http://www.lunatipower.com/CamSpecCard.aspx?partNumber=60204

It's the "In Closes 42.5 ABDC" in the above but that's @ .050" and not seat to seat.

Seat to seat is 64.0 which is what i used in the calculator and is in a cam file I wrote from the Lunati specs as they don't list seat to seat.

Here's the long version calculator that get's more precise.

Sorry didnt read the 'seat to seat part'

Using 64.0 I come up with a dynamic of 7.83

How do you calculate the seat to seat degree ?

 

[Mike]

You have an e-mail.

 

[oldtimr]

Sorry didnt read the 'seat to seat part'

Using 64.0 I come up with a dynamic of 7.83

How do you calculate the seat to seat degree ?

no calculating really, just addition and subtraction

276° advert dur
360 in a circle and 180 from tdc to bdc
icl at 106atdc(this WHERE 1/2 of advert OCCURS)
1/2 of 276 is 138
106 + 138= 244° ATDC
244-180= 64° ABDC

this assumes a symmetrical lobe I guess

 

[dougred]

Thanks for all the help. Am I getting the dynamic right at 7.83:1 ? If so I believe 91 octane would be enough and run 40deg of advance?

 

[oldtimr]

thereabouts

87 may run it fine

engine will tell you how much advance

http://www.chevelles.com/forums/showthread.php?p=915942&highlight=60204#post915942