4/7 Swap Cams
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