For a 149 tooth ring gear, that?s 360/149 = 2.4 degrees/tooth, so retarding by 3 teeth means 3*2.4 = 7.2 degrees. Might be a bit more than necessary. I do 1.5 teeth or 3.6 degrees.

Erich

It works out really well if you didn't install the jumper and still on the factory B curve. Nothing to come loose or break. Update my previous post.

Simple setup is, find TDC, then go 2 degrees past TDC on the downward stroke. Do the blow in tube or whatever sets TDC for your style EI, that takes two degrees off the base timing, then run the most conservative advance profile.

When LOP at higher altitudes you do not need much past 28 degrees maybe 29. At idle they do run nice with 30+ but who idles their plane everywhere :D

When ROP at sea level and take off, your traditional mag is actually firing the plugs around 23 degrees +/- a bit every time. This is how they were intended.

An EI fires very precisely every time. Think about the effect on effective timing and Theta PP.

For those who have never seen traces of cylinder pressure on a piston aero engine before, believe me it makes a difference.

Hope that helps. :)