We’ve offered serious cam discussions in the past; however, this month’s How It Works takes it to a whole new level. Cam tech is indeed a complex science, but the typical hot-button itemslike how duration and lift affect the power curve and how to set valve lashhave been covered in exhausting detail already in dozens upon dozens of past stories. The goal this time around is to focus on hard-core topics eating away at hard-core racers; if you want to know how to adjust your cam specs to help get your small-tire drag car hook, keep reading. For circle track racers wanting big power and rpm, but are limited by maximum valve lift rules, you’ll find helpful advice in the following pages. Got a set of 500-cfm Big Chief heads that flow to over a full inch of lift, but keep eating valvesprings? How about a Pro Stockcaliber motor that keeps bending cam cores like a wet noodle? We’ll reveal how to address these situations. True cam experts are sometimes harder to find, but fortunately, we’ve tapped into two of the sharpest minds in the industry. So in the words of Chris Mays of COMP Cams, and Nolan Jamora of Isky Racing Cams, here’s a healthy helping of some extra juicy camshaft tech.
Small Tire Racing Cams
Chris Mays: Whether it’s small tire drag racing or in oval track competition, we’re often faced with the challenge of trying to design cam specs around traction limitations. It’s a good problem to have, and it beats not having enough power. That said, shocking the tires isn’t a good thing. A very effective solution is to widen the lobe separation angle. The wider we can pull the LSA apart, the softer we hit the tires. This spreads the powerband out a little bit and moves the torque curve higher up in the rpm range. If that’s not enough, the second step is to add a few more degrees of duration on the intake lobe, exhaust lobe, or both. This effectively alters the shape of the torque curve. Every time you add duration, whether it’s on the intake or exhaust lobes, you move the torque curve higher up in the powerband. Sometimes, just adding 4-8 degrees of duration on the exhaust lobe and widening the LSA 1-2 degrees will be enough to make a car much easier to hook up at the track. These simple changes yield torque characteristics that are very similar to the original cam, but don’t dramatically alter the powerband. Putting these theories into practice, let’s say you have an Outlaw 10.5 car with a big-block that’s having trouble hooking up out of the hole. Since it makes so much power, how it runs from the 330-foot mark to the finish line is the most important aspect of how well it runs down the quarter-mile. Adding a few degrees of duration on the intake and exhaust and widening the LSA a couple of degrees can make a dramatic improvement in 60-foot times. The catch is that if you widen LSA too much, it will hurt midrange acceleration.
Nolan Jamora: In motors that make good power but blow the tires off, there are a few simple tuning tricks you can try at the track. The first step is to retard the cam a couple of degrees. That will move the torque band up a few hundred rpm, and give you more top end power. Another option is to play with the valve lash. If you want to lighten up the bottom end, you can loosen the lash. This will make the engine think the cam is smaller than it really is by opening up the intake valve later. As a result, the motor won’t hit the tires as hard, but will still have the same peak lift at high rpm. If neither of these changes are effective, the next step is to install a new cam with a wider lobe separation angle. Simply widening the LSA from 108 to 112 degrees will make a night and day difference in how quickly the torque curve comes on. At the track, a cam with a wider LSA won’t hit the tires until after the 60-foot mark, but still pull hard up top. For instance, we’re now using 114- to 116-degree LSAs in our Pro Stock camseven though they’re naturally aspiratedto prevent tire shake. In an extreme race application like this, a wider LSA doesn’t really sacrifice anything. It does sacrifice low-end torque a bit, but it won’t hurt the midrange at all.