Solid cams are very necessary in high-rpm, high-hp engines. Hydraulic cams with their function based on
oil pressure,
oil flow, heavy components etc, will float the valves way before a solid cam will (generally speaking). As a general rule in the back of my mind, hp peaks up to 5500-6000 usually get hydraulic cams. Over that and I usually recommend solids.
Solid flat tappet cams will last for a long, long, long time. Solid roller cams will last for a long, long, long time, but the lifters won't. Also, the spring pressures that are required for wild lobes and high rpms will wear a spring out, which necessitates spring maintenance.
You can get away with a much wilder lobe on a solid cam. A wilder lobe introduces more power. A wilder lobe will open the valve quicker, hold it open longer, and then set it back down quicker. There are limits with hydraulic cams, as you can bleed down a lifter if you get too funky.
There is a camshaft term called "major intensity". It's basically the difference between advertised duration and .050" duration. I'm not a cam grinder, I'm an engine builder, so my definitions won't be as in depth as say Mike Jones, Harold Brookshire, etc. could get with them. But when you sit back and look at a lobe's design, with how fast it opens, how long it's open (the duration at .200"), how fast it closes, the lift, and the major intensity, you can get an idea of how wild a cam is.
A hydraulic cam (say a Comp Cams Xtreme Energy lobe) has a MI of about 50-52°. Relatively speaking, the MI of a Comp Cams TK solid roller lobe is 28°. This means the difference between advertised and .050" duration is very low. Which means that things happen in a hurry. Valve opening is instant, the valve is open long, and valve close is instant.
If you tried to design a hydraulic cam with 28° MI, it would self destruct. But wild cam lobes is what makes a race engine a race engine.
Lash may make a cam's duration effectively smaller, but as an engine builder, you know to add duration to compensate. A hydraulic cam with a 230° duration at .050" will not behave the same as a solid cam with a 230° at .050". You usually have to add around 10° for a solid cam equivilent.
Lash ramps are made into a lobe's design for a reason. Again, I'm not a cam designer, but there has to be a specific amount of take-up in a cam lobe's design for it 1. to function correctly and 2. to not be ultra-violent. The purpose is basically to avoid high velocity collisions. There are such things as tight lash cams, but essentially, you need that lash ramp there so that the clearance is taken up slowly and all the valvetrain parts don't take a severe beating.
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