page_title: Helical camshaft
section_title: Profile
hierarchical_section_title: Helical camshaft / Profile
caption_attribution_description: English: Suzuki GSX 250 standard and helical camshafts. The helical cam is in its minimum duration position. The cams are positioned side-by-side to show that the cam profiles are virtually identical.
context_page_description: A helical camshaft is a type of mechanical variable valve actuation system. More specifically it is a camshaft that allows the valve opening duration to be varied over a wide, continuous, step-less range, with all of the added duration being at full valve lift.
  In this article a “variable duration camshaft” refers to a camshaft with a design that is intended to replace a conventional camshaft in a cylinder head and operate the valves through conventional followers. Further qualifications are:
  that the duration range is step-less and continuous
  all the added range is at full valve lift
  the range is wide enough to allow full torque/power at even extremely high RPM
  the range is wide enough to allow engine load control by late inlet valve closing
  the rates of valve opening/closing, acceleration, jerk etc. are within acceptable limits at all duration settings
  These qualifications must be made as there have been many claims over the years of purely mechanical variable duration camshafts but none have been able to meet all these requirements.
  Despite enormous effort and expense being expended by both large organisations and private individuals, camshaft arrangements like U.S.
context_section_description: The base or shortest duration profile of the helical camshaft system is almost identical to a standard production engine profile. The helical camshaft base profile belongs to the general group of lobe shapes which are used with pivoting cam followers, especially those with a fairly high rocker ratio, around 2:1.
  This family of lobe profiles is characterised primarily by having a short lobe lift. Because of this the lobe has a very rounded-off (or “snub-nosed”) appearance. The radius of curvature of the nose region (about the axis of rotation of the camshaft) is often very close to being a constant radius over an angular extent of about 20 degrees or so. A helical camshaft requires this region to be a true constant radius. In some cases this requires as little as 0.25 mm (or less) to be removed from the nose. When measured, the rates of acceleration and jerk in the nose region are slightly higher than standard.
  The lobe nose typically can have about 150° added to it, for extra duration. The lift surface geometry remains unchanged. Because of this extended duration the lift rate and total lift do not have to be as extreme as a racing cam to achieve maximum high end power.
caption: A comparison of the standard Suzuki camshaft lobe profile with the base duration profile of the helical camshaft shows that they are virtually identical.
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