Cam timing:

[oldeskewltoy]

Can peak lift(where it happens, NOT how much) change based only on changes in valve clearence??

Or said another way.... will peak lift change(again where it happens, not how much) if clearence is 1mm, or 0mm??

[jonathan yee]

thinking out my rectum, the smaller clearances you run the longer the duration would be and peak lift would be sooner and longer if only by a fraction.

but as clearances are a set value i'm not sure why it matters?

[wiso]

technically speaking I would say no. the peak of lift will always happen at the same point, as this is determined by the cam, not the valves. changing the clearances will change the opening and closing points. but not true peak. though it would be hard to find true peak when the ramp rate over the peak of the cam is so gradual.

having larger clearance does mean though at the peak the valve will be less open. but where it happens will not change

[wiso]

my shity diagram to support my theory



green being 0mm clearance, red being 1mm clearance. green is already opening by the time red starts to open. but both are same point on full lift.

[oldcorollas]

I say no.

the only way it could change the point of highest lift, would be if the axis of the cam was outside the bucket (to the side), otherwise when the cam is pointing vertically down, the same tip of the nose will always touch the bucket....

now.. if you have a roller follower, thats different, because the roller effectively gives you a highly curved bucket, and the point of highest lift is when the longest radii of the cam is pointing at the roller followers axis.
however, if by changing the cam axis, the follower doesn't move directly along that line, then the point and thus angle of intersection will change, and so the angle of max lift will change (relative to the original cam position only)

so basically, when changing clearances, if the arc of the rolle follower is such that it significantly changes the angle of the intersection between the cam and rollers axis (which is highly unlikely) then angle of lift will change..

but basically no

[oldeskewltoy]

the reason I asked is the current HKS cams appear to have different points in the duration depending on 1mm or 0mm of lift. OR have a read these incorrectly??

[oldcorollas]

reading incorrectly. 中央 means centre = lift centreline, 大 means big = peak lift(i can't see the other kanji)

for exhaust (for example)
if you set peak lift at 110deg, the centreline at 0mm lift will be at 102deg (ie if you measure from both sides of cam, and halve it)
for 1mm lift, the centreline will be 110deg

the centreline between open/close of 1mm lift is the same as the peak lift angle, but the 0mm lift (ie after clearance has been taken up) is different. this is because the 0-1mm opening and closing ramps are different.

that help?

edit: some cams have very assymetric lobes, so the centreline between two points of lift will change throughout the the cams lift.