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Camshaft Specification Sheet

How to Degree a Cam

Relevant Module: Worked Examples > Nissan SR20 > Introduction

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Hi, I have a question regarding the net valve lift calculation in the SR20 introduction work example at 1:52 in the video, where the camshaft specification sheet is show, and based on the given values cam lift intake 6.83mm, rocker 1.6, valve lash intake 0.20 and using the formula 6.83x1.6=10.93-0.20=10.73mm, and however the spec sheet lists 10.60mm instead. Could you please explain why there is a difference in both intake and exhaust values? Is the spec sheet correct, or is there another factor affecting the final value? Thanks.

Without going back and checking, i would suspect it's because the geometry isn't actually as nominal throughout the rocker's travel?

Depending on the specific rocker design, the pivot point is normally fixed, and the tip of the rocker moves in a known arc around the pivot, the problem is the point where the camshaft is acting on the rocker is constantly changing, and this is going to alter the actual ratio at that point.

There are some very useful, animated, videos on-line if you want to look for some - i'd do it myself, but got to pick up some med's.

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