'05 Setup Graph If you compare the baseline (blue line) to 8,000 rpm (red line) you can see several things. First, the spread from the opening is minimal. Toward the top of the lobe, you can see the valve is lofted slightly and follows the closing ramp. The line is away from the baseline so it has lost control, but, as you'll see later, it could be a lot worse. Notice the small blip at the bottom after the valve has closed. This indicates how much the valve is bouncing off the seat. In our car, this small amount won't tear things up. For 8,000 rpm, steel valves, and a stock cam, this isn't too bad.
'04 Setup Graph This graph shows several things. The opening line for 8,000 rpm is spread a lot farther than the previous graph. This is the pushrod flexing. As the pushrod releases its energy, it lofts the valve higher than the baseline. After that, it crashes back into the lifter and bounces back off the cam profile. When the valve closes, it does so with a lot more force and bounces the valve off the seat. This is out of control.
'06 Setup at 7,000 Graph For a stock cam profile, this looks decent. I'd guess the NMRA wanted to drop the rpm level between 1,500 and 2,000 rpm on the pushrod blower cars. This shows that we look fairly good at 7,000 rpm. Notice that there is little deflection as the cam opens the valve. Lower spring pressure helps this, as does a stiff pushrod. At full lift, the valve is close to the baseline trace. On the closing ramp, it follows the lobe well. After closing, the amount of bounce is minimal. Stock cam, stock lifters at 7,000 rpm.
Lofting The Valve Graph OK, here it is. We tried a couple of combinations and this was the result. We had heard about "engineered loft." It's possible to design in the ability to loft the cam, thus increasing effective lift. We're told the Cup guys run this type of setup. As you can see, the opening ramp is deflected so the pushrod has stored energy. Once it releases, the valve is tossed about 0.050 off the lobe. As it closes, it follows the closing ramp well. It does bounce the valve off the seat. I would bet a lot of racers are lofting their valves and don't know about it. Spring pressure must be maintained for all the conditions to be constant. If one cylinder has 20 more pounds of spring pressure, it won't have the same characteristics. Hmmm, I need to order a set of pistons with a lot of valve relief.
Out of Control Graph This graph is a lot like our setup from 2004. It's more dramatic in all areas. Notice the deflection at the opening followed by a rebound on the downside that actually is inverse of the baseline. The valve is slammed with such force that it bounces twice. After all the testing, we had to touch up the seats on our test heads. We could see the results of the pounding. Not everything we tried worked, and we even found a couple of things I had thought were good but weren't. This is what you get when you've lost control: broken valves, snapped rocker studs, keepers pulled through retainers, or broken lifters. All these failures can cost huge dollars. Spend a little time on your valvetrain. It's worth it.