I have been searching for material requirements for HR camshafts , so here is the latest wisdom on hydraulic roller vs. solid roller:

For an engine that will redline at less than 7000 rpm, the hydraulic roller is probably better. Also, IMHO, if you have to ask about vacuum, you should be looking at a hydraulic roller.

Now if you are looking for the last ounce of power in a race car and don't give a rat's tail about driveability, the solid roller is the answer.

There is significant overlap between the two types, more so now that so many hydraulic roller cams and engines are out there. That's what is in every new pushrod engine sold in the US.

OF COURSE you can buy a solid roller cam that will have excellent street manners, but why would you want to? Love that tic-tic-tic of the solid lifter? You already have the lifters and the retrofit hydraulics will cost $500? Those would be good reasons.

IF, however, you are starting from scratch the hydraulic roller has advantages and would be what I suggest.

R.