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Cam Tech - CHP How It WorksHard-core Cam Tech With the Experts From COMP Cams and Isky Racing From the April, 2011 issue of Chevy High Performance By Stephen Kim Photography by Stephen Kim
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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. 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. 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. Chris Mays: Turbo cars act very differently than supercharged or nitrous applications. For any given power level, a turbo motor doesn’t need much duration at all. Compared to a nitrous or blower car, the camshafts in turbo motors are much smaller. Since turbos operate off exhaust pressures, the main objective is to minimize overlap to prevent disrupting the exhaust pulses going to the turbo. If you go from blower to turbo but don’t change cam, the engine would have so much overlap that it couldn’t build boost like it needs to. In an effort to reduce turbo lag in street cars, we often use single-pattern or reverse-split cams that have 3-4 degrees less duration on the exhaust side than on the intake side. That’s because you don’t need much intake duration to fill the cylinder, but if you don’t have enough exhaust duration, the turbo will hit a wall at a certain rpm and run out of steam. What we’re doing is changing the exhaust duration to control the rpm range of the engine. Exhaust duration tremendously affects the operating rpm range of a turbo motor. Let’s say you have a mild turbo combo that turns 7,000 rpm with twin 67mm turbos, but then decide to get more aggressive with better heads, twin 88mm turbos, and a 9,200-rpm peak engine speed. To adjust the powerband, you would leave the intake duration the same while increasing exhaust duration. Chris Mays: Modern cylinder heads flow astounding volumes of air, and it’s not uncommon for big-block heads to achieve peak flow above 0.800-inch valve lift. A cam with that much lift would have spelled doom for the valvesprings many years ago, but that’s not the case anymore. Not only has valvetrain technology improved, through extensive testing we’ve learned various methods to increase spring longevity. With cylinder heads that flow to the 0.800- or 0.900-inch range, we tend to accelerate the valves more with rocker ratio than with the cam lobe. This allows backing off the acceleration rate of the cam. Stability in rocker arms and the rest of valvetrain is then crucial to prevent valve float. You need very light valves and retainers, and even smaller-diameter springs. This reduction in mass greatly reduces the stress on the valvetrain. The end result is a lot of lift with springs that last two to three times longer. Nolan Jamora: With as good as cylinder heads are these days, 0.800-inch lift isn’t that much for a big-block anymore. Some high-end big-blocks are now running 1.000- to 1.500-inch lift. At the Pro Stock level, valvespring pressure is now 1,200-1,400 pounds. This puts lots of stress on the valvetrain, and every piece of the puzzle is important in extending parts longevity. One of the biggest problems is trying to get the springs to live, and that requires a stable valvetrain. To accomplish this, we have developed our EZ roller lifter that utilizes bushings instead of needle bearings. This eliminates the lifter bounce associated with high spring pressure and rpm. Consequently, it has enabled us to design cam profiles that take advantage of this roller lifter. In the past, we used to employ very aggressive opening ramps, and match them up with gentle closing ramps to extend valvetrain life. The goal is to close the valve as smoothly as possible. Now we can design lobes in nine different sections. This allows us to design really short and steep ramps going up, but long, smooth ramps on closing side. These efforts dramatically improve the longevity of the valvetrain. 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. 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. 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. Chris Mays: In some high-end Chevy race engines, it’s not uncommon to switch the firing orders of the number 4 and 7 cylinders with a 4/7 swap camshaft. Some engine builders go one step further by swapping the firing orders of the number 2 and 3 cylinders as well. Any time this is done, you generally see a power increase. Changing the firing order tends to alleviate engine harmonics and improves the cooling properties. Bigger engines see bigger increases in horsepower, but it’s hard to put an exact figure on it. Even if the power increase is small, the improvements in harmonics and smoothness promote parts longevity, especially in high-rpm applications. Obviously, this isn’t something that’s intended for your average street car, but in extreme race applications it’s worth the investment. Furthermore, with these swap cams, exhaust system setup is very important. Some swap cams require tri-Y headers, and the lengths of primary tubes and merge collector design are very important. When installing one of these cams, unless the exhaust system is set up properly, you’ve done it for naught. Nolan Jamora: Typically, 4/7 swap cams help smooth engine harmonics and yield a more balanced intake charge from cylinder to cylinder. They’re usually found in high-end drag race engines and oval track applications. For the average bracket race engine that only turns 7,500 rpm, a 4/7 swap cam won’t help one bit, since you must have tremendous airflow to take advantage of them. Conversely, in an 8,800 rpm engine with lots of boost, a 4/7 swap cam helps balance things out. Chris Mays: When people hear the term lofting they get the impression that the lifters are flying off the cam lobes 0.5 inch, then eventually find their way back onto the closing ramp somewhere. In reality, it’s not nearly that extreme. In lift-limited racing classes, you can loft the lobes over the nose of the cam to get an extra 0.050 to 0.060 inch of lift, but that represents less than 1 percent of engine applications out there. In truth, every single application has a little bit of lofting, and it usually occurs close to peak power. This type of lofting is usually less than 0.010 to 0.020 inch, and isn’t intentionally designed into a cam as a performance enhancing tool. Likewise, lofting occurs more often if the valvetrain can’t control the design of cam as closely as it should. For instance, if you have a stock valvetrain and install a big cam, you will have lots of lofting. As camshaft designers, we’re trying to control or eliminate as much lofting as possible since it increases the potential for valve float. When the lifter lands, it sends shock waves through the rest of the valvetrain. This flexes the pushrods, decreases lift and duration, and hurts power. As rpm increase, the engine will go into valve float. In the small percentage of race engines where lofting can be advantageous, the valvetrain must have enough spring pressure and stability to prevent shock waves from pulsing through the valvetrain. Chris Mays: Nitriding is a process often performed on crankshafts, and COMP now offers it on camshafts as well. We call it Pro Plasma nitriding, and we have one of the only machines in the country that can perform the process. Nitriding involves introducing pulsed plasma nitrogen onto the steel surface of a camshaft in a vacuum-controlled environment. This increases the hardness and durability of the cam’s surface dramatically. It’s important to note that nitriding is not just a coating process. The nitrogen ions actually penetrate 0.008 inch and bond to the steel itself. The main reason we developed the procedure was to increase camshaft durability, especially with flat-tappets, to increase camshaft durability in extreme applications that use lots of valvespring pressure. With the reduction in key oil additives due to EPA restrictions, nitriding is more practical than ever before. So if you’ve had wear problems with a cam and want to stick with flat-tappet lifters, nitriding is a good route. We offer the service on any off-the-shelf or custom cam. CHP
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