Coupers, According to Light Plane Maintenance Aircraft Engine Operating Guide (Belvoir Publications/Kas Thomas), the RPM chosen by the manufacturer for doing a mag check is largely arbitrary. The 1800 to 2000 RPM run-up usually recommended is to some extent a carry over from the old days when big radial engines only turned up that much RPM at full throttle. Todays engines turn up higher speeds at full throttle, the prop tips are much closer to the ground (as compared to the older tail draggers), and full throttle run-ups can result in prop tip damage due to gravel, etc. The book says that the important thing is to do it the same way each time and to pay attention for any changes from one mag check to the next. He also says "The actual amount of RPM drop is not as important as smoothness, consistency between mags, and consistency from one runup to the next." He says that in some cases a drop of up to 200 RPM can be acceptable.
Hope this is of some help. Good Flying, Wayne DelRossi [EMAIL PROTECTED] Alon N5618F Simpsonville SC
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