Thread: compression issues

Tweet

I took physical measurements this morning and triple checked them:
BORE: 4.030
STROKE: 3.48
GASKET: 4.135 X 0.040
ACTUAL CHAMBER: 63.0cc
PISTON IN BORE: -0.3cc

SWEPT VOLUME (4.030)(4.030)(3.48)(PI/4)(16.387)=727.4cc
GASKET VOLUME (4.135)(4.135)(0.040)(0.7854)(16.387)=8.80cc
NET CHAMBER 63.0+8.80-0.3=71.5cc

SCR (727.4+71.5)/71.5=11.17

INTAKE CLOSED ON SEAT @65*ABDC MEASURED STROKE LEFT=2.697"

THIS WOULD CHANGE THE ABOVE SCR TO 8.88 FOR A MEASURED DCR.
IS THIS PRACTICAL FOR 89 OCTANE OR BETTER?

I still do not know why the two sets of heads under the same casting #'s and with no previous machining came up different, but I have them in my hands and know it is so. Now what can I do with what I have? I was thinking of putting the 76ers together but I dont like the numbers much. I could have the 64's machined for 2.02/1.6 valves with an unshroud sweep. this would open up the net chamber some but would it be enough? An additional 3.5cc would bring the DCR down to 8.516. Any thoughts?

Originally Posted by threearmsinjune

I took physical measurements this morning and triple checked them:
BORE: 4.030
STROKE: 3.48
GASKET: 4.135 X 0.040
ACTUAL CHAMBER: 63.0cc
PISTON IN BORE: -0.3cc

SWEPT VOLUME (4.030)(4.030)(3.48)(PI/4)(16.387)=727.4cc
GASKET VOLUME (4.135)(4.135)(0.040)(0.7854)(16.387)=8.80cc
NET CHAMBER 63.0+8.80-0.3=71.5cc

SCR (727.4+71.5)/71.5=11.17

INTAKE CLOSED ON SEAT @65*ABDC MEASURED STROKE LEFT=2.697"

THIS WOULD CHANGE THE ABOVE SCR TO 8.88 FOR A MEASURED DCR.
IS THIS PRACTICAL FOR 89 OCTANE OR BETTER?

I still do not know why the two sets of heads under the same casting #'s and with no previous machining came up different, but I have them in my hands and know it is so. Now what can I do with what I have? I was thinking of putting the 76ers together but I dont like the numbers much. I could have the 64's machined for 2.02/1.6 valves with an unshroud sweep. this would open up the net chamber some but would it be enough? An additional 3.5cc would bring the DCR down to 8.516. Any thoughts?

Have you cc'd the heads to make sure of the combustion chamber size??