There is lift/duration lost in the solid cam valve lash but the cam is ground to account for that. A hydraulic cam runs with no lash so introducing lash will result in loss. The loss in lift will be the lash X rocker ratio-about 1:1.4 on our cars and a few deg duration. Also the hydraulic ramps may not be able to deal with lash on solid ball studs. I think you can run a solid cam on hydraulic lifters but not the other way around. So you would gain lift/duration with a solid cam on hydraulic lifters. This is all hypothetical-you would want to check it out.

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Tony H
W111 280SE 3.5 Coupe
Manual transmission

Past cars:
Porsche 914 2.0
'64 Jaguar XKE Roadster
'57 Oval Window VW
'71 Toyota Hilux Pickup Truck-Dad bought new
'73 Toyota Celica GT