Cam: FP 4R Peak Power: 537 whp Power Curve: 3 Idle: 5 PrICe: $445 Notes: Another good cams
Cam: Kelford 272 Peak Power: 544 whp Power Curve: 4 Idle: 5 PrICe: $624 Notes: Average idl
As you can see from the acceleration graph on the right, one cam has much higher acceleration forces than the other. Guess which cam will be easier on the valvetrain?
This parameter is very important because if the valve is closed too fast, premature valve seat and valve wear will occur. We can actually go further and derive acceleration into jerk, which is the rate of change of acceleration. The car in my previous example that was accelerating at 2 mph per second isn't going to keep accelerating like that, it will eventually start to slow its acceleration as aerodynamic drag takes its toll. Jerk is also critical in calculating valvetrain loads and harmonics. I'll stop there as it can go even further than that. Cam lobe design is complex and many things need to be taken into consideration. Ideally, we want the valve open for as long as possible but to do so we need to open and close the valve quickly. It's a big game where the designer optimizes the lift profile to maximize gains while ensuring the valvetrain holds together. If the engine is designed for only drag racing, we can push the limit further as the operating time is much less than a road race engine for example. A purpose-built drag race engine might only see 30 trips down the dragstrip before a tear down, while an endurance engine might have to last the 24 hours of Daytona.
It's difficult to compare all of these camshafts and pick a winner. If I were drag racing the winner would be either Tomei 280's or the Crane's. If my car took me to work everyday and I did a few track days throughout the year I'd go with something more mild like the Forced Performance 4R's or the Kelford 272's. The very mild cams like the GReddy Easy Cams and HKS 272 would be more suited to the stock Evo turbo rather than the GT35R that I used.
BC Brian Crower