Pushrods
01-19-2015 | 07:55 AM
#21
MarineKinetics
Joined: Oct 2002
Posts: 942
Likes: 5
From: Rochester, NY
Pr
VC,
When approaching the optimal pushrod selection it is beneficial to approach the pushrod as a subsystem of the valve train rather than a standalone component. As always in the valve train, the clash of mass versus stiffness comes into play. A few general rules to think about;
Shorter is always better within the correct geometry. The buckling stiffness is inversely proportional to the square of the length of the column. For example, a 2.0” reduction in the length of a 12” pushrod would, for the same cross-sectional area, increase the critical load by a factor of 1.44.” (Thanks to Jack Kane for that math)
The key is to control the dynamic mass of the system while minimizing compliance in the pushrod. The additional PR length required in a tall deck application is a definite negative. Column width trumps wall thickness, however when you run out of real estate on diameter you can only move inward toward wall thickness.
In regards to the balance of mass versus stiffness in your pushrod selection, if you error off the optimal balance, you would always be best served to err on the side of increased stiffness with a slight mass penalty over less stiffness and increase compliance in the pushrod side of the system.
Bob
When approaching the optimal pushrod selection it is beneficial to approach the pushrod as a subsystem of the valve train rather than a standalone component. As always in the valve train, the clash of mass versus stiffness comes into play. A few general rules to think about;
Shorter is always better within the correct geometry. The buckling stiffness is inversely proportional to the square of the length of the column. For example, a 2.0” reduction in the length of a 12” pushrod would, for the same cross-sectional area, increase the critical load by a factor of 1.44.” (Thanks to Jack Kane for that math)
The key is to control the dynamic mass of the system while minimizing compliance in the pushrod. The additional PR length required in a tall deck application is a definite negative. Column width trumps wall thickness, however when you run out of real estate on diameter you can only move inward toward wall thickness.
In regards to the balance of mass versus stiffness in your pushrod selection, if you error off the optimal balance, you would always be best served to err on the side of increased stiffness with a slight mass penalty over less stiffness and increase compliance in the pushrod side of the system.
Bob
Last edited by rmbuilder; 01-19-2015 at 10:44 AM. Reason: spell
01-19-2015 | 08:12 AM
#22
Thread Starter
Gold Member
Joined: Sep 2011
Posts: 2,643
Likes: 18
From: cleveland ohio
We're going to call bob and ask his advice.
Just thought that maybe there were general parameters in a chart from or the like.
Thanks for all the replies fellas.
01-19-2015 | 08:15 AM
#23
Thread Starter
Gold Member
Joined: Sep 2011
Posts: 2,643
Likes: 18
From: cleveland ohio
VC,
When approaching the optimal pushrod selection is beneficial to approach the pushrod is a subsystem of the valve train rather than a standalone component. As always in the valve train, the clash of mass versus stiffness comes into play. A few general rules to think about;
Shorter is always better within the correct geometry. The buckling stiffness is inversely proportional to the square of the length of the column. For example, a 2.0” reduction in the length of a 12” pushrod would, for the same cross-sectional area, increase the critical load by a factor of 1.44.” (Thanks to Jack Kane for that math)
The key is to control the dynamic mass of the system while minimizing compliance in the pushrod. The additional PR length required in a tall deck application is a definite negative. Column width trumps wall thickness, however when you run out of real estate on diameter you can only move inward toward wall thickness.
In regards to the balance of mass versus stiffness in your pushrod selection, if you error off the optimal balance, you would always be best served to err on the side of increased stiffness with a slight mass penalty over less stiffness and increase compliance in the pushrod side of the system.
Bob
When approaching the optimal pushrod selection is beneficial to approach the pushrod is a subsystem of the valve train rather than a standalone component. As always in the valve train, the clash of mass versus stiffness comes into play. A few general rules to think about;
Shorter is always better within the correct geometry. The buckling stiffness is inversely proportional to the square of the length of the column. For example, a 2.0” reduction in the length of a 12” pushrod would, for the same cross-sectional area, increase the critical load by a factor of 1.44.” (Thanks to Jack Kane for that math)
The key is to control the dynamic mass of the system while minimizing compliance in the pushrod. The additional PR length required in a tall deck application is a definite negative. Column width trumps wall thickness, however when you run out of real estate on diameter you can only move inward toward wall thickness.
In regards to the balance of mass versus stiffness in your pushrod selection, if you error off the optimal balance, you would always be best served to err on the side of increased stiffness with a slight mass penalty over less stiffness and increase compliance in the pushrod side of the system.
Bob
