Quote:
Originally posted by camgrinder
To compare an RSR sprint cam with the Super cup cam,
The Rsr sprint intake has 280 degrees at 1mm and the Super cup has 242 degrees. Both have the same valve lift. The super cup intake cam accelerates the valve at a much higher rate than the Sprint.
Porsche engines have a very stable valvetrain compared to most engines. The biggest advantage to using an aftermarket valve springs is keeping the rocker arm in contact with the camshaft lobe. At higher rpms the lobe can cause a condition called "lofting" where the rocker arm leaves the cam lobe at full lift. This condition can cause more wear than the added valve spring pressure of a non stock valve spring.
Valves coming in contact with the piston is usually caused by valve seat bounce. Inadequate valve spring closed pressure at high rpm can cause the valve to bounce off of the seat when closing.
If you keep the 964 camshaft under 6800 rpms a new set of factory springs will be fine. Ti retainers would be a good investment. Hoping the valves wont hit the piston because you have added more room is not solving the problem. The valvetrain will be separating, the rocker arm not contacting the cam lobe or the rocker arm coming out of contact with the valve stem tip etc. When these parts come back into contact the force can be extremely high, causing broken rocker arms etc.
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Thanks John. That is just the sort of thing I wanted to know. I'll be calling.
-Chris