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 kommentar(er)
