[Grady Clay]

Chris,

You are correct; you don’t want any more valve spring than absolutely necessary. Strong valve springs add wear to the entire valve train. The crank gear to jack shaft gear sees more load, as to the chains, chain sprockets, cam and rockers. Even the tensioner and probably the valve guides also. Besides it uses horsepower and causes heat just where you don’t want it.

With low compression piston (T, E, CIS…) there is not much valve cut-out. If the valve contacts the piston it is at one side of the perimeter of the valve. This almost always bends the valve.

With high compression pistons (S, C6, RSR…) the valve cut-out matches the full circumference of the valve. In an over-rev situation the piston can just help close the valve by contact. Not desirable but not necessarily bending the valve.

Of course the type of cam has a great deal to do with this. With some cams, the piston chases the valves closed and the valves chase the piston down. There are situations where the closest valve-to-piston clearance is not when the valve is at maximum lift or the piston at TDC.

FWIW, I have never had or built a street or race engine with anything other than stock valve springs set to stock settings.

Best,
Grady