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YIO390 EXP w/E Mags

rockitdoc

rockitdoc

Well Known Member
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My 390 came with two E Mags and Denso IKH27 plugs. They were gapped 0.030" from Lycoming. I presume this is correct, but I can't find anything in the Lycoming manual on this.
 
rockitdoc said:
My 390 came with two E Mags and Denso IKH27 plugs. They were gapped 0.030" from Lycoming. I presume this is correct, but I can't find anything in the Lycoming manual on this.
Click to expand...
Yeah, and suggest you download the EMag manual. It has this and a lot of other great info.
 
The torque curve on a Lycoming Hemispherical combustion chamber piston engine is very flat at maximum torque. More advance timing only brings it closer to detonation and raises cylinder temperature without much in the way of more horsepower.
 
What Full Trottle said, no advantage to lots of advance, plus:
Spec is 20* on angle valve, keep it as close to that as possible during the critical break-in to keep it cool.
IMO Pmags and angle valve engines aren't a great combination.
 
The dual pMags I installed on an RV-14A IO-390 had timing set at engine label base, 20 degrees. Following the pMag install manual, this translates to the pMag timing set when the crank is at 5 degrees ATDC. The pMags were with jumper in so max advance was 9 degree (the advance at the most extreme low manifold pressure - as in very high altitude).

The pMags have been flying for 8 years of so in this RV-14A and have been flawless. CHT were below 400 degrees during break in. After break in CHT continued to decline into the mid 300 range.

Carl
 
What Carl said.
How about instead of 5-10 degree ATDC, go with 5 which is the standard and then cap the advance shift to another 4 or 5.
 
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