Posted By: MikeN
Lower valve spring pressure-what rev limit? - 08/12/15 09:34 PM
I intend to use softer valve springs than the original ones to avoid any problems with the flat tappet camshaft.
A rough calculation says that the living force is proportional to engine speed over 2 and consequently that a spring with half the spring rate will need a 30 % reduction of the maximum speed. Friction will in some way affect this. But how much? What is your experiences during run in on soft valve springs?
In this case the engine is a 426 Hemi with MP 1970 specification repro hydraulic camshaft (pn 4529315). Standard/factory open spring pressure is 320 lb. Designed valve float speed is 6800 rpm with this combination. One alternative is to use a spring with 230 lb open pressure (Comp Cams 920). If the formula above works, valve float speed will be 5700 rpm. I will put the revlimter on 5200 rpm (and accept a power loss). Do the numbers seem reasonably?
If the lifters would “pump up” slightly in a hemi, how will it be noticed? Power reduction or immediate failure?
A rough calculation says that the living force is proportional to engine speed over 2 and consequently that a spring with half the spring rate will need a 30 % reduction of the maximum speed. Friction will in some way affect this. But how much? What is your experiences during run in on soft valve springs?
In this case the engine is a 426 Hemi with MP 1970 specification repro hydraulic camshaft (pn 4529315). Standard/factory open spring pressure is 320 lb. Designed valve float speed is 6800 rpm with this combination. One alternative is to use a spring with 230 lb open pressure (Comp Cams 920). If the formula above works, valve float speed will be 5700 rpm. I will put the revlimter on 5200 rpm (and accept a power loss). Do the numbers seem reasonably?
If the lifters would “pump up” slightly in a hemi, how will it be noticed? Power reduction or immediate failure?