what are the differences and benefits between mechanical and hydraulic cams?

That's a pretty big question

Here is an over simplified answer:

Difference:
Solid lifter is just that. Lifter is solid and has no compliance. Hydraulic lifter uses a hollow cylinder housing with a piston and spring. Engine oil fills the cylinder under the piston. There is compliance with a hydraulic lifter.

Benefits to solid lifter cam:
more agressive profiles to allow better breathing
higher rpm limits without worry of lifter pump or sink

Benefits to Hydraulic cam:
Quiet operation
more tolerant to ignorance

You will hear people say that you have to constantly adjust solid lifters. (IMO) they've got their heads up their ass, or they are parroting the wrong people. I've gone over 60K miles without even looking at adjustment on solid lifter cams. There are only two reasons to re-adjust solid lifters. Valve recession and valve-train wear. Both of these have more to do with picking the wrong stuff, or poor assembly techniques, than the fact it's a solid lifter.

FWIW; I rarely suggest a solid lifter for a non-racing application, unless the person really knows what (s)he is doing, and has optimized the entire engine/drivtrain package. Hydraulic cams and valve-train are too good now to really see the benefit for anything less than racing.

to add to what 66runt said, solid lifter cams have longer opening and closing ramps to allow for the valve lash to be taken up softly to prevent hammering the valvetrain. hydraulic lifters dont need said ramps because the leak down feature built into the lifters does the same thing.

66Runt said:

You will hear people say that you have to constantly adjust solid lifters. (IMO) they've got their heads up their ass, or they are parroting the wrong people. I've gone over 60K miles without even looking at adjustment on solid lifter cams. There are only two reasons to re-adjust solid lifters. Valve recession and valve-train wear. Both of these have more to do with picking the wrong stuff, or poor assembly techniques, than the fact it's a solid lifter.

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My theory is that this urban legend came from the factory use of adjustment nuts with no polylocks. The nuts would back off a bit and you'd need to tighten them up. If the rockers stay put, you're right, only valve recession or cam/lifter wear would cause the clearances to grow.

The factory adjustables arent that great. The threads get loose and what not and they will not hold adjustment too well. One question, how can you tell a mechanical cam vs a hydraulic cam. Can you look at it and tell? Is it in the hardness or angle of the lobes?

brin0357 said:

One question, how can you tell a mechanical cam vs a hydraulic cam. Can you look at it and tell? Is it in the hardness or angle of the lobes?

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you cant tell by looking. you have to have the timing card that comes with the cam. one thing, you can put hydraulic lifters on a solid lifter cam, but NOT the other way around. if you do put hydraulic lifters on a soid lifter cam though, you will have much more duration and valve overlap to contend with, and it usually hurts low end performance.

Interesting, we have cams laying all over our shop and sometimes I will measure them too see how much lift they have got. Some of them are pretty big, but I wonder if they are a solid or hydrauliuc cam. Why would you have more duration?

brin0357 said:

Interesting, we have cams laying all over our shop and sometimes I will measure them too see how much lift they have got. Some of them are pretty big, but I wonder if they are a solid or hydrauliuc cam. Why would you have more duration?

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the added duration comes from the longer opening and closing ramps built into the solid lifter cam to prevent hammering the valvetrain. as long as you use solid lifters on a solid lifter cam, you get the advertised duration, but if you use hydraulic lifters on a solid lifter cam you get about 20 degrees more duration or so depending on the grind because the hydraulic lifters already have a cushioning effect built in, so the ramps add duration with hydraulic lifters.

I think you end up with less duration putting a hydraulic lifter on a solid cam. it would absorb a little on the opening event, and maybe even a little lift.

The added duration of a hydraulic lifter over a solid is also due to decreased lash clearances. Solid lifters typically require .012"-.030" of lash. A hydraulic lifter uses a preload which equates to zero lash.

Typically a solid will appear to loose somewhere around 6 degrees over its rated duration.

At least that is the way it was explained to me. . . . .