What about the theory that a little runout may be a good thing. I've been told that it may "help the valve lay down softly" I'm a bit skeptical about that explanation. I sorta always figured the better the runout (which is a combination of position control (true position) and feature control (roundness) the better the potential for a perfect seal.

Steve

 

Never heard that one Steve.

The job of the camshaft's closing ramp is to do just that.... ease the transition to the seat. Endurance and street cams are obviously smoother but some jerk is expected in drag race stuff if you want to make big HP.

The problem with poor concentricity is the valve is seeing a side load every time it contacts that section of the seat. That's going to increase guide wear and that just compounds the problem. Enough heating, loading and it may just say to heck with it, I'm outta here.

-Mindgame

 

Agree.

Virtually all valves bounce on the seat when they close at high revs. I picture the eccentric valve doing the "hootchie cootchie" dance as it bounces on the seat. (I'm reading Smokey's memoir and pick up on his lingo). As 'Game said, the valve should take an early exit.

The clearance between the stem and the guide alows the valve a little room to "find" the seat.