Knowing how to interpret cam specs and how they interact to affect engine performance is o
One of the trends that is clear from the evolution of the performance cam is the move toward faster action, with more lift for a given amount of duration. The faster the valves are opened, the more torque the engine will generally make within a given rpm range. As Mays from COMP tells us: “The surrounding parts around the camshaft have just gotten so much better that it allows us to use much quicker-acting camshafts. You see the OEMs doing the same thing.” Things like better springs, more rigid valvetrain components, and lighter parts, especially in the valves, springs, and retainers, make the difference. Many of the cam lobes offered today deliver lift in the range of race cams of old, and do it within a duration window that would have been unheard of back in the day. By allowing more lift, these modern cams make more torque over a broader operating range, and they work hand in hand with modern high-flowing cylinder heads to tap into the high-lift flow.
Says from Lunati points out: “You always hear the word aggressive used to describe these fast lobe profiles. What that means is you can make a broader torque curve without giving up any power by shortening the seat duration and increasing the area under the lift curve by increasing the duration at higher lifts. As the acceleration rate increases, however, it can increase wear, and it becomes more difficult to keep the system stable. The lighter the components the better, especially in the retainers, locks, and valves. The weight of the lifter itself is less critical, while with pushrods, strength and stiffness are the more important factors.”
The cam must be properly phased to the crankshaft when it is installed. The position of th
The Combination Counts
An engine is an assembly of interrelated parts, and just how these parts work together means everything to the power output. Cam selection will follow the engine combination. Jon Kaase brought home the point by comparing the effects of changes in the cam and heads in relation to power output: “If the engine doesn’t have very good heads on it and you put quite a bit of cam in it, it still will not make a whole lot of power, it will just run poorly down low. These two parts complement each other. Take for example a big-block Ford with a big cam, but it has a set of stock cast-iron 460 Ford heads. If you swap to our P51 heads, then it might pick up 100-200 hp. If you do it the other way around and have a really mild cam and add the set of heads, you might just pick up 20-30 hp. Then, you change the cam and pick up 100 hp. If you have a lot of cam in it and a stock head, the cam doesn’t help very much, but if you have no cam in it and change the heads, the good set of heads don’t do as much as they might. They pretty much have to go together.”
The right cam doesn’t just stop at the engine, it also depends upon what the user’s goals are. Mays from COMP relates: "I might have a guy with a 6-71 blown small-block rear-engine dragster doing nostalgia racing, or I might have exactly the same engine configuration, but the guy runs a Willys coupe street car, and he just wants it to sound good and drive it. You can’t cam those two applications the same, even if the motors are identical."
Go to www.popularhotrodding.com to read a comprehensive glossary of camshaft terms, keyword search: "camshaft basics."