Issue with Stamped Steel Rockers in BB Chevy

[Jesse Knapp]

SS Div. 6. I, too, thought duration was the culpret. When you allow the valve to stay open longer it must close rapidly or there could be clearance problems. Doesn't excessive duration cause some of these problems stockers are having? I do know if your ramp design allows for quick closing, the spring pressure has to be increased or that valve will bounce. Wouldn't you say all these things are the root of the rocker arm problems? And then the roller rockers and girdles will solve everything until they remove the stock lift rule then the Jesel system will be necessary. Where does it stop? Your posts are excellent, by the way.

[SSDiv6]

Originally Posted by Jesse Knapp

SS Div. 6. I, too, thought duration was the culpret. When you allow the valve to stay open longer it must close rapidly or there could be clearance problems. Doesn't excessive duration cause some of these problems stockers are having? I do know if your ramp design allows for quick closing, the spring pressure has to be increased or that valve will bounce. Wouldn't you say all these things are the root of the rocker arm problems? And then the roller rockers and girdles will solve everything until they remove the stock lift rule then the Jesel system will be necessary. Where does it stop? Your posts are excellent, by the way.

Jesse, one problem I have seen with many engines is cams with the wrong duration. Dwell on the following statement: If you keep the cylinder filled for too long, how efficiently can you evacuate the cylinder during the exhaust event? What happens to the remaining exhaust? Think about it...you have a stalled port that happens to have an effect on the valve loading. It exuberates the valve train dynamics, especially at high RPM's.

It is also a function of efficient cylinder filling: you have to take in to account the cylinder head flow, velocity, stroke, rod length, valve size, piston, etc...for your camshaft design. The area under the curve will determine how good your cam performs. One of the biggest problems with the wrong duration and incorrect camshaft events is reversion. I have lost count on how many engines I have seen with this problem. Signs of reversion is a sooty intake manifold plenum and exhaust. Also, when your engine does not respond to jetting or fuel curve changes, most of the times you have a reversion problem.

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.

[Jesse Knapp]

Originally Posted by SSDiv6

Jesse, one problem I have seen with many engines is cams with the wrong duration. Dwell on the following statement: If you keep the cylinder filled for too long, how efficiently can you evacuate the cylinder during the exhaust event? What happens to the remaining exhaust? Think about it...you have a stalled port that happens to have an effect on the valve loading. It exuberates the valve train dynamics, especially at high RPM's.

It is also a function of efficient cylinder filling: you have to take in to account the cylinder head flow, velocity, stroke, rod length, valve size, piston, etc...for your camshaft design. The area under the curve will determine how good your cam performs. One of the biggest problems with the wrong duration and incorrect camshaft events is reversion. I have lost count on how many engines I have seen with this problem. Signs of reversion is a sooty intake manifold plenum and exhaust. Also, when your engine does not respond to jetting or fuel curve changes, most of the times you have a reversion problem.

I am familiar with reversion and the loss of power it causes. So, too much duration can allow unburned fuel into the exhaust and exhaust gases into and contaminating the fresh fuel charge, or reversion. Since all heads flow differently and velocity is determined by piston seal I believe, two identical engines can or would require different cam duration since stroke, rod length, valves and pistons are identical. I thought reversion was caused not as much by length of time a valve is open, but by when it opens and closes. My apology for drifting from the original thread title. It's gotten interesting for me.

[SSDiv6]

Originally Posted by Jesse Knapp

I am familiar with reversion and the loss of power it causes. So, too much duration can allow unburned fuel into the exhaust and exhaust gases into and contaminating the fresh fuel charge, or reversion. Since all heads flow differently and velocity is determined by piston seal I believe, two identical engines can or would require different cam duration since stroke, rod length, valves and pistons are identical. I thought reversion was caused not as much by length of time a valve is open, but by when it opens and closes. My apology for drifting from the original thread title. It's gotten interesting for me.

Do not worry about the drifting from the subject...it is all related. Yes, you got it...that is the reason why I shy away from using the same grind for the same application, unless my analysis shows that I am close enough to run the same grind.