Loves302Chevy
"One test is worth a thousand expert opinions."
I searched, but I can't find the simple answer to this question:
This pertains to a GEN 1 SB Chevy using a flat-tappet Crane CompuCam 2050. cam #114142
Cam manufacturers recommend seat and valve open spring pressures usually using 1.5 ratio rockers. I will be using 1.6 ratio rockers. Do I choose my spring and installed height based on the 1.5 ratio, and the increased pressure resulting from the 1.6 rocker is a good thing - or do I want to have the specified pressures using the 1.6 rockers?
Let me give an example: this cam calls for 114# at the seat and 318# valve open. The valve lifts are .454/.480 (1.5) and change to .484/.512 (1.6). I'm considering an Elgin spring #9914XK with the following specs: 1.260 OD single with damper, .876 ID, 125#@1.750, 325#@1.250, CB at 1.160, and .530 max lift. I calculate a spring rate of 400#/in. If I set this spring to 1.780 installed height, I get 113# on the seat and 317# at .512 lift (exhaust with 1.6). Am I doing this correctly? If I were to use the 1.6 rockers on the INTAKES ONLY, the math gets easier because the numbers would be nearly the same at .484 INTAKE and .480 EXHAUST. I have an assortment of retainers and locks to set an installed height ranging from 1.720" to 1.865" using the stock length valves.
Thanks again, Mike.
This pertains to a GEN 1 SB Chevy using a flat-tappet Crane CompuCam 2050. cam #114142
Cam manufacturers recommend seat and valve open spring pressures usually using 1.5 ratio rockers. I will be using 1.6 ratio rockers. Do I choose my spring and installed height based on the 1.5 ratio, and the increased pressure resulting from the 1.6 rocker is a good thing - or do I want to have the specified pressures using the 1.6 rockers?
Let me give an example: this cam calls for 114# at the seat and 318# valve open. The valve lifts are .454/.480 (1.5) and change to .484/.512 (1.6). I'm considering an Elgin spring #9914XK with the following specs: 1.260 OD single with damper, .876 ID, 125#@1.750, 325#@1.250, CB at 1.160, and .530 max lift. I calculate a spring rate of 400#/in. If I set this spring to 1.780 installed height, I get 113# on the seat and 317# at .512 lift (exhaust with 1.6). Am I doing this correctly? If I were to use the 1.6 rockers on the INTAKES ONLY, the math gets easier because the numbers would be nearly the same at .484 INTAKE and .480 EXHAUST. I have an assortment of retainers and locks to set an installed height ranging from 1.720" to 1.865" using the stock length valves.
Thanks again, Mike.