Questions about CR/cams/milled head/headgasket
07-28-2003, 05:49 PM
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Questions about CR/cams/milled head/headgasket
OK. I need to ask the pros some questions. First here is the setup:
JDM b16a with stock bottom end
JUN III cams and JUN cam gears
Head milled .030 with a 1 layer headgasket.
After looking further into the setup I became very worried about valve clearances with the cam/mill/hg combo. So I got the idea to pull the head and add a thicker headgasket. After some searching I found Cometic makes a hg that is .036in. This being ~.006 thicker than the stock gasket. So basically by adding .006 to the hg, I turn the actual mill of the head into .024. I feel this combo may be safer to run the JUN IIIs and allow me minimal use of the cam gears. Now by using the c-speed comp calc ( http://www.c-speedracing.com/howto/...lc/compcalc.php) with a stock JDM motor and that .036 hg, that gives me a CR of 10.21~1. Now by using another formula that uses the mill of the head, I get a CR of 11.13~1. Is this sufficient compression to make good use of the cams? Also, with a milled head, how should I adjust the gears to give me close to 0,0? How much can I adjust the gears until I run into problems? Maybe 3 degrees? 2? Now Cometic makes another hg that's .043, which will give me more clearance, but that will lower my compression to 10.89. Which I think is too low for those cams. Are there any other quality headgasket companies around? Any input is appreciated. I want to get this thing right so I don't ruin it the first time it goes into VTEC. BTW here is the other formula for the CR:
CCV = combustion chamber volume
CV = cylinder volume
MHV = milled head volume
CR = ( CCV + CV ) / CCV
To calculate CV (cylinder volume)
CV = (stroke) x (bore)^2 x (Pi/4)
CV = 7.7 cm x 8.1 cm^2 x .7853981633974
CV = 396.8 cc
To calculate CCV (combustion chamber volume)
Rearranging the equation CR = (CCV + CV) / CCV
CCV = CV / (CR - 1)
CCV = 396.8 cc / (10.2 - 1) = 43.1 cc
To calculate MHV (milled head volume)
(amount head was milled) x (bore)^2 x (Pi/4)
.030" mill off the head = .076cm
MHV = (0.076 cm) x (8.1 cm)^2 x .7853981633974 = 3.92 cc.
To calculate new CCV with milled head
CCV = CCV = 43.1 cc - 3.92 cc = 39.2 cc
To calculate new CR with milled head
CR = ( CCV + CV ) / CCV
CR = (39.2 cc + 396.8 cc) / 39.2 cc
CR = 11.12:1
JDM b16a with stock bottom end
JUN III cams and JUN cam gears
Head milled .030 with a 1 layer headgasket.
After looking further into the setup I became very worried about valve clearances with the cam/mill/hg combo. So I got the idea to pull the head and add a thicker headgasket. After some searching I found Cometic makes a hg that is .036in. This being ~.006 thicker than the stock gasket. So basically by adding .006 to the hg, I turn the actual mill of the head into .024. I feel this combo may be safer to run the JUN IIIs and allow me minimal use of the cam gears. Now by using the c-speed comp calc ( http://www.c-speedracing.com/howto/...lc/compcalc.php) with a stock JDM motor and that .036 hg, that gives me a CR of 10.21~1. Now by using another formula that uses the mill of the head, I get a CR of 11.13~1. Is this sufficient compression to make good use of the cams? Also, with a milled head, how should I adjust the gears to give me close to 0,0? How much can I adjust the gears until I run into problems? Maybe 3 degrees? 2? Now Cometic makes another hg that's .043, which will give me more clearance, but that will lower my compression to 10.89. Which I think is too low for those cams. Are there any other quality headgasket companies around? Any input is appreciated. I want to get this thing right so I don't ruin it the first time it goes into VTEC. BTW here is the other formula for the CR:
CCV = combustion chamber volume
CV = cylinder volume
MHV = milled head volume
CR = ( CCV + CV ) / CCV
To calculate CV (cylinder volume)
CV = (stroke) x (bore)^2 x (Pi/4)
CV = 7.7 cm x 8.1 cm^2 x .7853981633974
CV = 396.8 cc
To calculate CCV (combustion chamber volume)
Rearranging the equation CR = (CCV + CV) / CCV
CCV = CV / (CR - 1)
CCV = 396.8 cc / (10.2 - 1) = 43.1 cc
To calculate MHV (milled head volume)
(amount head was milled) x (bore)^2 x (Pi/4)
.030" mill off the head = .076cm
MHV = (0.076 cm) x (8.1 cm)^2 x .7853981633974 = 3.92 cc.
To calculate new CCV with milled head
CCV = CCV = 43.1 cc - 3.92 cc = 39.2 cc
To calculate new CR with milled head
CR = ( CCV + CV ) / CCV
CR = (39.2 cc + 396.8 cc) / 39.2 cc
CR = 11.12:1
