Preload for Performance
Discussion
Ok so in theory a hydraulic lifter can lift whatever preload is put into it (what with liquid being virtually incompressible)
And the RV8 calls for between 20 and 60 thou of preload in the lifter before oil enters.
Thus when the lifters are full they are pushing the valves open whatever lift is on the cam + whatever preload put into lifters then subject to rocker ratio (1.6 in RV8 case)
Therefore there must be a point over 60 thou preload where there is a possibility of the valve staying open when on the heel of the cam and the piston striking the valve when on full lift if too much is applied?
Am I correct in my assumptions so far?
If so it follows that for a performance application it is vital that maximum safe preload is attained - that is to say one that satisfies both the above.
I have been setting my preload to 40 thou but in theory if it could take another 40 or so then should I do it? I would need to check that valves are closing (compression test) and check piston crown clearance (plasticine)
After all, whats the point in getting stage 3 heads, big valves and enlarged manifolds if the valves aren't even opening to their full potential! scratchchin
And the RV8 calls for between 20 and 60 thou of preload in the lifter before oil enters.
Thus when the lifters are full they are pushing the valves open whatever lift is on the cam + whatever preload put into lifters then subject to rocker ratio (1.6 in RV8 case)
Therefore there must be a point over 60 thou preload where there is a possibility of the valve staying open when on the heel of the cam and the piston striking the valve when on full lift if too much is applied?
Am I correct in my assumptions so far?
If so it follows that for a performance application it is vital that maximum safe preload is attained - that is to say one that satisfies both the above.
I have been setting my preload to 40 thou but in theory if it could take another 40 or so then should I do it? I would need to check that valves are closing (compression test) and check piston crown clearance (plasticine)
After all, whats the point in getting stage 3 heads, big valves and enlarged manifolds if the valves aren't even opening to their full potential! scratchchin
phazed said:
Given the above, it would be a good idea to go solid cam..
you'll be good for maybe 10 horses and they wont bleed down in hot track conditions.
It would indeed Peter but I already have a nice shiny new Crower 50234 in my workshop that I brought back from the USA (Ever tried taking a Cam through security in your hand luggage?!!)you'll be good for maybe 10 horses and they wont bleed down in hot track conditions.
preload shouldn't affect valve lift....
Its to allow enough movement so that the hydraulic chamber fills with oil and goes past the 'shutoff ~ topping up' valve-ing? Then it should be in the range that the hydraulic chamber can pump up / deflate to ensure the follower just kisses the pushrod ~> valvetrain when the valve is closed. 20-30 thou either way & it just adapts to that state...
You can get the valve failing to seat if the lifters pump up at the higher oil pressure seen at top revs, much depends on the actual followers, effects could start even as low as 5000rpm on some variants. As Peter mentioned if you were serious a solid cam is the answer, hydraulics are 'woolly' however you look at it. Much easier to shoot a guy tied down to a chair than an idiot running round in haphazard fashion
Its to allow enough movement so that the hydraulic chamber fills with oil and goes past the 'shutoff ~ topping up' valve-ing? Then it should be in the range that the hydraulic chamber can pump up / deflate to ensure the follower just kisses the pushrod ~> valvetrain when the valve is closed. 20-30 thou either way & it just adapts to that state...
You can get the valve failing to seat if the lifters pump up at the higher oil pressure seen at top revs, much depends on the actual followers, effects could start even as low as 5000rpm on some variants. As Peter mentioned if you were serious a solid cam is the answer, hydraulics are 'woolly' however you look at it. Much easier to shoot a guy tied down to a chair than an idiot running round in haphazard fashion
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