![]() Hydraulic or Solid?įlat tappet and roller cams for overhead valve engines are available with hydraulic and mechanical lifters. If you need proof that roller cams are better, ask the OEMs what they put in their engines nowadays. That means a roller can make more midrange and top-end power than a flat tappet cam of the same duration without sacrificing bottom-end power. This design dramatically decreases valvetrain friction and wear, and allows designers to create profiles that offer more lift without increasing duration. Roller cams are hardened steel cams that use lifters with a roller, or wheel, that rolls over the cam lobes. With literally hundreds of profiles to choose from, finding a good flat tappet cam for your street car is not difficult. Virtually every V8 engine built before the late-1980s came with a flat tappet cam they are reliable and relatively inexpensive. Flat tappet cams use a lifter with a slightly curved bottom that slides against the cam lobes. Now that you have an idea of what lift and duration are, let’s muddy things up by comparing flat tappet and roller lifter cams. Again, much depends on the overall engine combination and intended use, but as a general rule, cams with a 110-to 112- degree LSA offer good power and decent street manners. A cam with a narrow LSA (104-108 degrees) offers greater low and midrange torque production, but a narrower operating range, a choppy idle, and less engine vacuum.įor the street, you want a cam that offers a compromise–decent idle quality, respectable vacuum for operating power brakes and such, and good overall power production. That translates into a wider rpm range, better idle quality, and higher engine vacuum, but at the cost of less torque at low and midrange rpm. Generally, a cam with wider LSA (112-116 degrees) offers less overlap between intake and exhaust opening and closing events. LSA helps determine the cam’s behavior you can take a given set of lift and duration figures, change the LSA, and get cams with vastly different characteristics. Lobe Separation Angle, or LSA, is the number of degrees that separate the peak lift points of the cam’s intake and exhaust lobes. Two cams may be very close in advertised duration, for example, but make peak power at different rpms. Since all cam grinders use this measurement, it’s a much more accurate way to compare a wide variety of camshafts. The problem with advertised duration is cam makers use various methods of measuring it, making it difficult to compare cams from different makers. ![]() Because it doesn’t keep the valves open as long, a smaller cam boosts low rpm torque and drivability.Īdvertised Duration is the figure you usually see in the cam ads and hear about at those late-night bench races. A shorter duration cam does just the opposite. This keeps the valves open longer, increasing midrange and top-end power at the expense of low-end torque. When someone talks about a “big” cam, they are referring to cams with longer duration. ![]() Virtually every cam maker uses duration to rate camshafts. ![]() The trick is to “size” a cam to optimize valvetrain events for your particular engine combination and vehicle. The more valve area open to flow, the more power an engine can theoretically make. Lift and duration combined determine total open valve area-the space available for air and fuel to flow into and out of the combustion chamber. Duration is the amount of time a cam keeps a valve off of its seat, measured in degrees of crank rotation. Lift is the amount a cam lobe actually moves a valve off its seat and is measured in fractions of an inch. Lift and duration are the primary factors that determine a cam’s profile. We’re going to concentrate on the basics you’ll need to know to choose a good street cam, and later we’ll share with you the key information you’ll need to supply your sales rep when purchasing a cam. Camshaft theory is a complex subject that can take a book-length article to explain. The result was overcammed engines that sounded great and could crank serious top-end power, but were not very streetable and couldn’t idle to save their lives.īut thanks to modern cam technology, you can come pretty darn close to the Holy Grail of street bumpsticks-cams that make high rpm power, have good low-end torque and drivability, decent vacuum for power brakes, and that loping idle we all love. Not so long ago, the bigger is better philosophy reigned supreme regarding camshafts. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |