440 CAM SELECTION
03-23-2010, 06:06 PM
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440 CAM SELECTION
I am working on a rebuilt 73 440. Block has been decked .030, flattop pistons, no notches, .040 thick head gasket, 906 heads. Current Comp cam has 274/286 duration with .488/.491 lift. Is it possible to go to a hotter cam without the notched pistons? I guess I am asking what the limit is with this combination. Any help would be much appreciated.
03-23-2010, 07:54 PM
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Sorry but you're going to have to measure the actual valve to piston clearance. Do a Google search on ''how to measure valve to piston clearance". No way around this.
03-30-2010, 10:57 AM
#4
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my mopar b/rb book says 509 lift hyd cam was made to work without clearance issues , using std pistons . but who knows whats been done before you got your hands on it . so it should be measured . one other thing is the duration starts to climb quite a bit also with the larger lift cams & those std pistons really won't make sufficient compression . there are some reasonably cheap 1.6 ratio roller rockers around that would increase your lift to about 502 - 514 lift ( guessing off the top of my head ) without increasing duration much, you'll need to check valve springs also .
04-07-2010, 12:05 PM
#6
Mopar Fanatic
my mopar b/rb book says 509 lift hyd cam was made to work without clearance issues , using std pistons . but who knows whats been done before you got your hands on it . so it should be measured . one other thing is the duration starts to climb quite a bit also with the larger lift cams & those std pistons really won't make sufficient compression . there are some reasonably cheap 1.6 ratio roller rockers around that would increase your lift to about 502 - 514 lift ( guessing off the top of my head ) without increasing duration much, you'll need to check valve springs also .
I didn't do the math but here is the formula, and the answer is yes duration and overlap will play a part in the clearance also...
CAM LIFT OR LOBE LIFT X ROCKER RATIO = GROSS VALVE LIFT
THIS LEADS ME TO THE NEXT FORMULA TO DETERMINE MY GROSS VALVE LIFT IF I CHANGE MY ROCKER RATIO SUCH AS , INSTALLING 1.6 SBC ROCKERS WITH A COMP. CAMS XTREME ENERGY # XE 268H CAMSHAFT. CURRENT LISTING STATES .477/.480 LI9FT w/1.5 ROCKERS
VALVE LIFT ÷ ROCKER RATIO = LOBE LIFT [ CAM LIFT ]
LOBE LIFT X ROCKER RATIO = GROSS VALVE LIFT
EXAMPLE: .477 ÷ 1.5 = .318 [ LOBE LIFT ]
.318 X 1.6 = .5088 [ GROSS VALVE LIFT ]
NOTE: IF THE CAM HAS A DIFFERENT LIFT FOR THE EXHAUST, USE THE SAME FORMULA FOR THE EXHAUST. ALL OTHER SPEC'S FOR THE CAMSHAFT REMAIN THE SAME.
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