Issue with Stamped Steel Rockers in BB Chevy

[Chris Hill]

Jason,

It does not matter if the valve is hollow or solid, just the mass of the valve. But you can not ignore the stiffness of the valve itself. Some of the cup guys have tried very light intake valves, specifically very light heads of the valve. They ran into issues where the valve started to bounce off the seat due to the valve itself not being stiff enough when the valve hits the seat. You have to look at the entire valvetrain stiffness, including the cam bearing journals, bending stiffness of the camshaft between journals, valve stiffness, and valve seat stiffness. Generally, the least stiff member of the valvetrain is the rockerarm. And you only include roughly 1/3 of the mass of the rocker in your effective valvetrain mass. Some of your cup teams are using steel rockers instead of aluminum, as this drives the total valvetrain stiffness up without driving up the valvetrain effective mass.

Jeff Lee,

The beehive does help with decreased mass, but it also helps the valvespring harmonics issue. A beehive spring does not have constant stiffness and thus not a constant natural frequency. If a system does not have a constant natural frequency, harmonics are not as much of an issue. That is a very big reason nitrogen air springs are used in F1 and very high end motorcycle racing engines. Yes, air springs are light, but the very large decrease in valvespring harmonics is a big plus as well.

SSDiv6,

You may want to contact SAE about your proposed book, as I know they are looking for more valvetrain information. But then you would reveal yourself  A very old book exists by Michael Turkish that is the main valvetrain book I’ve read, plus internal research from my previous company. I know SAE recently published a book in the past couple of years about valvetrains, but I have not had an opportunity to view it yet.

On the poor angle issues on the small block MoPars and others, I agree the angularity will increase the force ratio in the valvetrain. For instance the rocker ratio may be 1.5, but the actual force applied between the pushrod and lifter cup may be 1.7~1.8. In my opinion, the increase in force ratio will increase the loading on the rocker arm, but not enough to cause rockerarm failure with out allot of lash and the subsequent impact loading. If you don’t believe me, take your peak valvetrain kinematic acceleration (generally during opening at approximately ¼ to 1/3 lift) and look at the stress on the rocker arm. You will find a pretty large safety factor for stress in the rockerarm. The only way to break it is impact stress.

Warren Johnson wrote a great article in the Dragster about this years ago, I'll try to find it and post it.

Chris, Hollow valves that are filled with sodium. It acts like a dead blow hammer when it hits the seat. Use something in the hollowed out area. Use your imagination and then get back with me.

[JRyan]

SSDiv6,

I think you mean EXACERBATE, which is "to increase severity or violence", as opposed to EXUBERATE, which is "to make things happy". Also, I've never seen "overfilling a cylinder" as a problem. If that were the case, supercharging wouldn't work.

Jerry

[SSDiv6]

Originally Posted by JRyan

SSDiv6,

I think you mean EXACERBATE, which is "to increase severity or violence", as opposed to EXUBERATE, which is "to make things happy". Also, I've never seen "overfilling a cylinder" as a problem. If that were the case, supercharging wouldn't work.

Jerry

Jerry, thank you for the correction...hard to type after a 15 hour work day!!! In regards to over filling a cylinder as a problem, superchargers and turbos are RPM controlled. Also, they have means to control the excess of pressure by relieving the pressure when they reach certain levels. A normally aspirated engine does not have those means, therefore you use the cam timing events to do so. I spent enough time with the Series I and Series II GM Supercharged engines and saw too many engines blow up when guys changed the settings on the boost control selenoid. Camshafts for supercharged and turbo engines have timing events completely different than the current Stocker grinds, especially in the overlap numbers to alleviate reversion.

[Dwight Southerland]

Originally Posted by Chris Hill

The beehive does help with decreased mass, but it also helps the valvespring harmonics issue. A beehive spring does not have constant stiffness and thus not a constant natural frequency. If a system does not have a constant natural frequency, harmonics are not as much of an issue.

. . . take your peak valvetrain kinematic acceleration (generally during opening at approximately ¼ to 1/3 lift) and look at the stress on the rocker arm. You will find a pretty large safety factor for stress in the rockerarm. The only way to break it is impact stress.

Scientific evidence is on your side in both issues. Smart camshaft designers work with this information constantly in the forefront of their design.