Martin,
What are the advantages of solid lifters? Jim
Several.
1. For a given duration number at .050" tappet lift, a solid cam will have significantly less seat duration, giving a better idle and more torque down low (shuts the intake valve sooner for more cylinder pressure). 1Tony1's cam has 20 degrees less seat duration than a hydraulic roller of the same duration @ .050". A popular hydraulic roller cam I sell is 232 @ .050" on the intake. It will idle good and not make the car go rich with a stock computer. When running a solid, we can go up to about 240 @ .050" and still maintain good vacuum, or good enough to prevent a rich idle..
2. Less valve float. We can run slightly more spring pressure on a solid cam and keep the valvetrain "happy".
3. Valve "loft". Valve loft, put simply, is mild valve float. You don't hear about it much. It starts when the valve is at full lift. The inertia of the valve will cause it to keep lifting past what the camshaft tells it to, giving it more lift and "area under the curve" for better cylinder filling. About halfway down the closing ramp the valve "catches up" and sets the lifter back down on the lobe and the camshaft shuts the valve softly. Full fledged valve float is the next progression, where the valvetrain does not come back into line before the valve event is over and slams the valve down on the seat, causing a lot of damage. Valve loft is used in most forms of professional racing. All of the Nextel Cup cars you watch on TV loft the valves approximtely .050" over the nose. NHRA Pro Stockers loft them over .100".
A hydraulic roller cam will not tolerate this. It cannot have any valve loft at all or the lifters will "pump up" and hang the valves off the seat when the cam shuts them. An example would be if you had .050" lifter preload, and you loft the valves. The "slack" in the valvetrain will allow the plunger in the lifter to pump up all the way until the clip stops it. .050" tappet lift X 1.7 rocker ratio = .085" valve lift. That's how far the valves would be open when they are supposed to be shut under valve float or loft. When the lifters bleed back down the valves will shut again.
Hope this explains things a little.