<div class='quotetop'>QUOTE(motoxlifer &#064; Jan 23 2006, 08&#58;36 PM) [snapback]42010[/snapback]</div>
Does anyone know why GM did this?
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All of the LSX cams prior to the LS6 had the same base circle radius. There was a problem with that base circle, if we wanted to go to higher lifts: the nose of the cam would approach the same diameter as the cam bearing journals or even above them. The only alternatives were to increase rocker arm ratio or reduce the base circle radius. GM decided to go with the base circle reduction. The ’01 base circle reduction did not require a change in dimensions of any other valve train part, however, the 405-horse cam was a different story. Because the position of the plunger within the hydraulic lifter is not optimal any more–you’re too high in the lifter. There’s different ways to correct the geometry. The one selected to minimize the impact on manufacturing operations was to increase the length of the valve. The valves in the 02 LS6 are 0.6-mm. longer than the valves in all other Gen III engines. With .025-in more intake lift, the same intake duration at .050-in but a little less duration at lash and the same rev limit; something had to be done to the rest of the valve train to keep it in control at high rpm. While the ’02 exhaust lobe doesn’t have quite the agressive profile as the intake, it’s still got more lift, so something had to be done there, too. The choices GM made were to decrease valve weight and increase valve spring pressure. With the higher lift, GM needed to reduce the mass of the valvetrain or start getting into a float condition. GM went to hollow stem intake and exhaust valves, very similar to what we used in the ’96 LT4. GM pushed the edge with a state-of-the-art, 0.8-mm. very thin stuff. The exhaust stems are sodium-potassium filled.

BTW, most of this explanation is a quote by "Hicks" (GM).

Hope this helps.