The new LS6 cam has a valve lift of .525-inch intake, and .525-inch exhaust, compared to .500/.500 for the MY00 Y-car LS1 profile. Measured at .050-inch tappet lift, LS6 intake duration is 204 degrees and exhaust is 211 degrees. The LS1 for MY00 was 198/208 degrees. The LS6 lobe centers are 116 degrees apart where as LS1 has them at 115.5 degrees. At .050-inch tappet lift, both cams have no overlap, but at .005 lift, LS6 overlap is 45 degrees and LS1 is 49 degrees. The overlap numbers make the new cam seem less aggressive, but that's clearly not the case.
This power and torque graph...
This power and torque graph of the 1990-92 LT5 vs. the 1997-00 LS1 vs. the 2001 LS6 is a revealing piece of information. There's no doubt that the LS6 either matches or exceeds the early version of the LT5 in all areas of the torque and power curves. In the mid-range the LS6 generates noticeably more torque. Also evident is that, in spite of a more aggressive camshaft, bigger intake ports, and more plenum volume, the LS6 equals or exceeds the LS1 in low-end torque.
Even though the LS1 looks like it has more overlap based on degrees, the LS6 actually has more overlap based on lift area: .52 versus .42 inch-degrees. That is why it's better to use lift area to quantify a lot of this cam data rather than just degrees.
We agree. With today's varying lobe configurations, comparing cams by the area under the profile is a better choice. Another issue to consider is, up to now, virtually all Gen III camshaft duration data released by GM's various communications entities has been "altered" to facilitate comparison to Gen I and Gen II small-block V-8 profiles which, except for the LT4, used 1.5 rocker ratios. These specifications are not skewed to a specific rocker ratio. Again, the duration numbers in degrees, when used for comparison purposes, can be deceiving. The lift area, in inch/degree, is a more consistent method of measurement.
Why does the LS6 have more actual overlap when, measured by duration in degrees, it appears not to? The LS6 valve accelerations and open/close ramp configurations are dramatically different from those of the LS1. The accelerations are higher, especially the negative acceleration over the nose, which increased about 10 percent. That's where the increased lift and duration come from. GM's engineers also changed the ramps. In the '97 model year they put constant velocity opening and closing ramps on the cam to limit valvetrain noise. For 2001, because (LS6) is a more aggressive application, they went back to a constant acceleration opening and closing which moves the valve faster. That gives more lift area and allows tighter lobe centers (than with constant velocity ramps having the same lift).
Obviously, with more lift, duration, higher acceleration rates and more usable rpm, the LS6 needs a more aggressive valve spring. The LS6 spring is made of different material (chrome/silicon/vanadium steel wire vs LS1's chrome/silicon steel wire) and has a different wire shape (oval vs. round), as well as being wound more tightly. These three features make a big difference in valve spring pressure: on the seat, 90 pounds for the LS6 vs. 76 pounds for the LS1, and over the nose, 260 pounds for the LS6 vs. 220 pounds for LS1.
Side view cuts of the LS6...
Side view cuts of the LS6 (left) and LS1 exhaust ports, again, show a smoother short-turn radius. On the piece at left you can also see some of the change to the combustion chamber. Note how the chamber wall around the spark plug has been moved in towards the valves and the roof has been lowered. Photo: GMPT Communications
The rest of the LS1 valvetrain, including the 1.7:1 investment cast steel, roller-fulcrum rockers carry over to the LS6. Generally, the Gen III valvetrain is more robust and lighter than the Gen II/I pieces. The natural frequency of the Gen III valvetrain is 740 Hz where as the old small-blocks were in the high 600s. This is why the Gen IIIs can rev higher than production Gen Is and IIs.
Cylinder Heads: The Ruthless Pursuit of Power
The same basic, performance characteristics of the LS1 head are used in the LS6 unit: 356-T6 aluminum casting, replicated ports offering the charge air a straight shot down to the intake valve, 15- degree valve angle, 2.00-inch intake valves and 1.55-inch exhausts with three angle faces and seats, head bolt and rocker stud bosses and oil return holes located such that they impact the intake ports as little as possible.
The major change in the LS6 intake port was alteration of the port's "short turn" or "short side" radius, the area of the port just upstream of the valve where the port floor curves down to the valve seat. The LS1 port suffered an air flow stall at high valve lift, induced by the short-turn radius and the goal was to eliminate that.