Different spring needs for solid vs hyd lifters on a hyd roller cam. Also - a roller sold as solid AND hydraulic

[dave brode]

Sold as hyd:
285/240, .640"
spring called for: 140/350#

Sold as solid
280/240, 640" lash - .018"
spring called for: 210/500+

Is this odd? that aside, would the solid lifters on a wildish street hyd roller lobe require different spring [for the same max rpm]?

Thanks.
Dave

[CamKing]

The difference is in the lash point.
Hydraulic profiles are designed with a ramp height between .004" and .006", and then the lift curve accelerates from there.
If you run mechanical lifters on it, and set the lash at the lash point multiplied by the rocker ratio, you wouldn't need more spring pressure.
If you set the lash above that, the lash point will be above the end of the ramp, and valve velocity/acceleration on and off the seat will be much higher. This increase in velocity/acceleration on and off the seat, will require more spring pressure to control the valvetrain.

[Walter R. Malik]

Sold as hyd:
285/240, .640"
spring called for: 140/350#

Sold as solid
280/240, 640" lash - .018"
spring called for: 210/500+

Is this odd? that aside, would the solid lifters on a wildish street hyd roller lobe require different spring [for the same max rpm]?

Thanks.
Dave

Using a "tight lash", (hydraulic type .006"/.008" ramps), don't seem to be a problem with cast iron block using cast iron heads however, when aluminum heads or especially aluminum blocks enter the picture, the expansion rates of the material won't allow that tight of hot lash and still allow the valves to close when cold.
In those cases, some kind of hydraulic adjustment faction must be used or there is a need for more lash.

[dave brode]

Thanks, Gents.

[tjs44]

FWIW,years ago when Comp cam out with their high lobe lift(400)hyd roller cams I bought a complete setup.After getting it I called Dean Harvey at Comp and asked how he felt running them over 6500.He called me back,had me send the kit back and they sent me a solid roller kit and told me to set them at 6 thou and have 200 on the seats.In other words treat it like a solid roller cam.Tom