Lift-Limited Classes

Chris Mays: In Super Stock or circle track classes, you’re often forced to work around rules that limit maximum lift, which presents a huge challenge for cam designers. In essence, you have to reverse-engineer existing lobe profiles. If maximum lift is limited to 0.450 inch, then you have to get as aggressive with the lobe profile as possible. Imagine how much harder it would be for Evel Knievel to jump the Grand Canyon if you shortened his landing ramp by 100 feet. That’s what you’re doing by trying to pack lots of area under the lift curve without a lot of maximum lift to work with. Likewise, all this acceleration needs to happen before peak lift. Due to how rapidly the lifter is accelerated, you’re going to get a certain amount of lofting over nose of camshaft. The trick is to control lofting so the lifter isn’t crashing violently onto the exhaust ramp. Furthermore, some of these classes also have cranking compression rules, which can be manipulated through the duration and LSA. Since the average racer can’t afford to buy 10 different camshafts, we put tremendous time into the design and testing process to ensure a certain cam will work before releasing it to the public. The Spintron is a huge asset in validation testing.

Nolan Jamora: At Isky, we specialize in designing cams for racing classes that limit lift or have a vacuum requirement. The challenge is getting these motors to run at high rpm. In order to get lots of rpm with low lift, you have to increase the duration. For example, our hydraulic 292 mega cam has 244-at-0.050 degrees of intake duration, 0.505-inch valve lift, and an operating range of 3,000 to 7,000 rpm. For many oval track classes lift is limited to 0.450 inch, so we have to adapt this cam profile accordingly. Due to its more conservative lift, the oval track version of the 292 mega cam has 288 degrees of advertised duration instead of 292, but its duration at 0.050-inch lift is the same at 244 degrees. In other words, the lift of each cam is very different, but their durations are very similar. With the low-lift cam, once the valve is open we leave it open longer. So while it doesn’t open the valve as much, it stays open longer to fill it with the air/fuel charge. We also shorten the LSA from 108 to 106 degrees with the oval track cam. As a result, the oval track cam comes into its powerband at 2,800 rpm, but still pulls hard to 7,000. In comparison, the 292 mega cam has a 3,000- to 7,000-rpm powerband. The differences in advertised duration between the two cams make a big difference in how they behave at the dragstrip. A car with the 0.450-inch lift cam would get a better 60 foot, but by the midrange a car with the 0.505-inch lift cam would fly right by it. On an oval track, a car with the 0.450-inch lift cam would pull away coming out of the turn, and right before the braking point, the car with the 0.505-inch cam would start to catch up but still be behind. At the 20-lap mark on a 3/8- to 1/2-mile track, the car with the smaller cam would be one lap ahead.