ptuomov

Is that simply because the nose is the weak point in the cam and the pressure on the cam nose at max lift goes down with the rpm? Or is it something more complicated related to lubrication?

Lizard928

From my research it is mainly from the lack of lubrication at the camshaft at idle.

Mike Simard

It's because there's no momentum or 'lofting' of the valve at low speeds and the nose and flanks see full spring pressure. That full spring pressure 'rubbing' is significant. If the lubrication isn't up to snuff it's even harder on the cam.
At higher speeds the nose doesn't see full valve spring force as the valve is well in motion as the acceleration decreases toward mid point and the spring cannot overcome the inertia to press against the cam with its full force.

GregBBRD

No, welded S-4 cams, from Web Cams will not have the same lobe centers as GT cams.

mark kibort

can you just grind off 1mm of base circle and hope that the lifters pump up more?

danglerb

Greg doesn't "hope" when he builds a motor.

Is there some hard limit in how much can be changed like lobe centers when a cam is welded and ground?

RyanPerrella

HA HA

ptuomov

That's what I meant by the pressure on the nose going down with the rpm. I guess it's more accurate to say that the pressure declines when the rpm increases in the negative acceleration region of the profile. Is that why you emphasized the "and"?

By the same logic, the pressure on the flank in the positive acceleration region must go up with the rpm, so it's not that the entire flank is less stressed at high rpm.

I can see two reasons why that part of the flank is not a big deal, though. First, it may be that the nose is pointier and, therefore, the effective contact patch smaller and the pressure higher. Second, and probably more importantly, the lift and therefore the spring force is lower at the positive acceleration region of the lobe.

I am curious about all this camshaft design stuff. Do you set up the design problem as a constrained optimization problem?

ptuomov

I wouldn't be surprised that if you grind and weld and grind, you can move them as much as you want. The more relevant questions are how cost (in)effective this is and does Webcam's price include moving the LCA (no).

danglerb

I gave them a set of 1980 16v cams and they gave me back the .507 lift long duration hot rod cams, but I don't know if lobe centers changed or how much. The told me cost was the same regardless of which cams I started with, low lift 1980, better 1979, or Euro S.

andy-gts

I have a set of gts cams with the base circle ground for more lift...if you are interested, the lobe centers are same as standard gts.