Using the data recorded by the Cam Analyzer we can look at the valve lift curves. Let's follow a lift curve and see what's going on. The valve lift curve shows crank rotation in degrees along the bottom (x-axis) and valve lift along the side (y-axis). Starting from left to right, we see the exhaust valve starting to open. This is the opening ramp, where it gently starts to lift the valve off the seat and into the main opening ramp. Near the peak lift of the cam the valve slows down and starts to head down the main closing ramp. As the valve gets closer to fully closing on the seat, the motion slows down and the valve gets gently set down. If this gently closing ramp wasn't there, the valve would get slammed onto its seat, possibly bouncing it off, causing damage and losing power. You can see that even though the exhaust valve isn't fully closed, the intake valve is starting to open. This is the period of overlap that I talked about earlier. I'll discuss overlap in more detail in the next article. Ideally we'd want to open the valve as fast as possible, hold it open, and then close it as fast as possible. Physical limitations of the valvetrain simply don't allow for this, and careful consideration must be taken to how fast valves open and close. Aggressive cam profiles require strong valvesprings to control valve motion and can even cause valvetrain components to wear out quickly. The design of camshafts is complex and great consideration must be taken into the power and longevity requirements of the engine. An endurance motor that has to run 500 miles of high-rpm running needs different cam profiles than an all-out drag race motor that only sees very limited run time. The Performance Trends Cam Analyzer can show the important data of a cam profile that determines many of the critical components needed for cam applications. For the average street tuner car this means choosing a cam that's not overly aggressive on the valve motions so that the engine lives worry free for thousands of miles. The Cam Analyzer helps me see the valve motion, and correlate valve opening and closing events with power gains on the dyno. The next and final article will cover valve events for the intake and exhaust, and help bring to light why some cams might idle better and some just make tons of power at high rpm.
Results: Stock Cams
What can I say, they're stock. They idle like butter at 900 rpm and have zero low-speed driveability issues. At 22 psi they pushed 418 whp, quite a bit lower than all the other cams and almost 100 whp down from last month's test of the Tomei 280 cams. Turning the boost up to 30 psi, the power climbed to 505 whp.
Forced Performance 4R cams
Idle quality is decent, while not as good as the mild HKS 272s, it's much better than the aggressive Tomei and Crane offerings. A few pulls later to dial the fuel in and the car made 465 whp at 22 psi, whereas at 30 psi I got 536 whp. After a few timing changes with the cams gears, the best power curve is found as per the recommended installed specs.
BC Brian Crower Stage 3:
The BC Brian Crower Stage 3 cams have a very similar idle quality and low-speed driveability to the FP4Rs. On power pulls, the power came in at 451 whp at 22 psi, and 527 whp at 30 psi. The BC Brian Crower Stage 3's did require some adjustment on the cam gears to get them to the factory specifications. While most cams were within 1 degree when checking out the specs on the stand, these cams had to be retarded 3 degrees on the intake and advanced 2 degrees on the exhaust side to check out. For an experiment I put them at zero, as if someone installed them without degreeing them, and the idle and power output suffered. This was a prime example why checking cam timing is important.
Comparing all three horsepower curves at 22 and 30 psi.
Next month's issue will bring a few more new cams, and I'll go into each particular valve timing event and why it affects the way the engine runs. I'll also look at specific cams and compare lift curves and valve events to see why they do or don't work.