Avstar Aircraft of Washington, Inc.

10415 172nd St. E., Hangar A1
Puyallup, WA  98374
office (253)770-9964
or (253)770-0120
email:  avstarair@att.net

05-18-2009 Ask Mike! Question
IO-550 Magnetos

Hi, Mike,

In the latest issue of the ABS magazine, top of page 11302, there is a mention of "1200 series mags" as possibly increasing the power of an IO-550 engine.  Do you know what sort of magnetos those are, and whether they would make a difference?

Take care,

Hello, Raymond;

In context, the author discussed the cylinder work and the Ram cam, as well as the mags.  The 550B is rated at 300 +5%/-0, so a well tuned one could be capable of 315.

I do not know what type of mags you have, but if recollection serves, the 550's seem to be split 50/50 between the 1200's and the Slick 6300's.  If you can't see the data plates, you can look at the mags and tell the difference by the harness attach plate:  4 screws is a Bendix 20/200 series, 4 nuts is Bendix 1200 series or 3 screws is a Slick 6300 series.

The 1200 series is the largest Bendix (now TCM) mag made.  If it actually has more available output voltage, I don't know.  There is no listing I have ever found on that.

There are also no listings on the magnetism of the rotors or magnet poles in the various mags.  By feel, I can tell you the magnetic pull after the null (negative magnet position) is about the same.  But the coil secondary resistance values of the TCM 20/200 series, 1200 series and Slick 6300 series are 12K-16K, 20K-26K and 13K-20.5K, respectively.  You can make of that what you desire, but that tells me the 1200's might be the strongest.  Worth the change?  I wouldn't think so.

Gear Green,