Issue with Stamped Steel Rockers in BB Chevy

[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.