Cam Tech - CHP How It Works

Hard-core Cam Tech With the Experts From COMP Cams and Isky Racing

Stephen Kim Feb 22, 2011 0 Comment(s)
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Flat-Tappet Power

Chris Mays: Solid roller cams offer the ultimate in performance, but solid flat-tappet cams are much more capable than many people realize. When comparing an extreme solid flat-tappet cam to an extreme hydraulic roller, the flat-tappet will make more power. Hydraulic roller cams have come a long way in the last 10 years, and they don’t give up as much power to a nice solid flat-tappet cam as they used to. However, solid flat-tappet racing cams have tons of area under the curve, and much of that is a result of the development work done by NASCAR Sprint Cup teams. You can’t accelerate the ramps quite as much on the nose of a solid flat-tappet cam as you can with a hydraulic roller, but there are ways to work around that. By installing a larger-diameter lifter, its larger footprint moves the edge of the tappet closer to the cam lobes. This picks the valves up more quickly very early in the lift curve. Another option is to use higher rocker arm ratios to accelerate the valves more quickly.

LSA

Chris Mays: When people compare different camshaft specs, they don’t consider that two cams can have the same lobe separation angle, but very different overlap. For instance, you can have a 220-at-0.050 cam and a 280-at-0.050, both on 110-degree LSAs. While these two cams might have the same LSA, the longer-duration cam has much more overlap. In an extreme case like this, it’s really an apples-to-pizza comparison. In order for LSA to accurately represent the overlap of a camshaft, you have to look at its duration specs to help put it into context. Tighter LSAs tends to boost low-end torque and narrow up the powerband. This is why short-duration cams are usually ground on wider LSAs than long-duration cams. The torque curve is already narrow with cams like that due to their short duration, so there’s no sense in tightening up the LSA.

Nolan Jamora: The prevailing trend today is to use a wide LSA on small-tire cars. It’s not uncommon to go as wide as a 118 to 120 degrees to make the low-end torque more manageable. These cams still make great peak power, but the difference is where in the rpm range the power starts coming in. On the other end of the spectrum, you don’t want to run a wide LSA in a heavy car with 14-inch-wide tires. You need the torque down low to move the car out of the hole. Generally, a 108- to 110-degree LSA works well in street cars since they offer a good mix of low-end torque, top end power, and idle quality. On the other hand, monster truck and truck pulling engines work best with a 102- to 104-degree LSA. Likewise, a heavy Super Stock drag car might need a 102-degree LSA to help get it out of the hole. Oval track cars are somewhere in between at around a 106-degree LSA.

Cam Deflection

Chris Mays: As valvespring pressures increase, cam flex can become an issue. This isn’t a concern in your typical street/strip application, but very much an issue in high-end drag racing and circle track engines. For example, if you put a standard-journal big-block cam in a motor with 1,300 pounds of open valvespring pressure, the cam will flex 0.010 to 0.015 inch between each journal. This flex changes the effective valve lift and duration that the motor sees. To combat flex, we can increase the size and number of journals. In NHRA Pro Stock, for instance, they use 70mm cam journals, which is about a 1/2-inch larger than a standard big-block. Plus, they use nine-bearing cam cores instead of a five-bearing core. Now you only have two cam lobes that are seeing the spring loads instead of four lobes. By creating more of a bridge between lobes and increasing the journal diameter, 98 percent of the cam flex can be eliminated. This obviously requires an aftermarket block, but blocks with larger cam tunnel bores are readily available these days.

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