N941WR
Legacy Member
AI have a 180 HP O-360 clone engine in my RV fired by a pair of 114 series P-mags.
Due to some of the comments on this site regarding high CHT's, I decided to play with the timing on my engine.
The parallel valve 8.5:1 compression O-360's standard magneto timing is 25 degrees Before Top Dead Center (BTDC). (This is basically the default timing for most parallel valve engines, check your manual for the timing for your engine and don't take my word for this!)
The P-mags have two basic settings, called the "A" and the "B" curve.
The P-mags have a six wire electrical connector that is used to attach the ground wire (Pin 1), positive (Pin 5) and negative (Pin 4) power leads, tach signal (Pin 6), and two connectors to provide serial send and receive signals (Pins 2 & 3).
There are five ways to adjust the timing on the P-mags.
1. Add a jumper between pins 2 & 3. No jumper and you are running on the "B" curve. Put a jumper in and you run on the "A" curve.
2. Modify the "B" curve using the EICAD program provided on the Emag website.
3. Manually set Top Dead Center off a few degrees
4. Install an EICommander and use that to manage (and monitor) your P-mags.
5. Develop your own management tool.
Since I just happen to have an EICommander installed in my plane, I will go with option #4. (Full disclosure: I am one of the principles involved with the development and marketing of the EICommander.)
A little definition here, the "A" curve (Jumper in) starts at around 26 degrees BTDC and allows the engine to advance to close to 30 degrees. The "B" curve (Jumper out) starts at close to 29 degrees and allows for an advance close to 34 degrees.
Since a number of people wrongly believe that if they run on the more advanced "B" curve they will get more power, I decided to try flying my plane on the "B" curve. With the EICommander, switching between the two curves or creating a custom one is only a few key punches away. (I prefer the term "configuration" over "curve" since you really aren't changing the curve, only shifting where you run on a pre-defined curve but for simplicity, we will call them all "curves".)
While running the engine on the "B" Curve (Jumper out), I was surprised to find my CHT's running right around 400 degrees F (+/- 5*F) and using a lot of fuel to keep them cool. Climbs were a challenge because I had to keep my airspeed up to keep the CHT's under control.
After two flights with this setting I went back to the "A" curve (Jumper in) and my CHT's immediately dropped 20 to 30 degrees F with no noticeable change in performance. There might have been a change but it would probably take a dyno to measure it.
Now the reason for this post. If you are experiencing higher than desired CHT's, check to make sure the timing of your ignition matches the recommendation of your engine manufacture.
While my timing was only off 5 degrees, the CHT difference surprised me.
If you have an angle valve engine, chances are your timing should be 20 degrees BTDC. (Check your manual!) If you are running P-mags without the jumper installed, you are running 10 degrees off and may not be doing yourself any favors. Even with the jumper in, you are still five degrees off.
I strongly suggest you download the EICAD program, connect a PC to each of your P-mags, and add a negative shift to get the timing down where it belongs.
If you have a parallel valve engine that requires 25 degrees BTDC timing and are running P-mags, put the jumper in.
The advance limits are only used at lower power settings and shouldn't be an issue.
Your cylinders will thank you for the lower temps and you might just pick up some additional performance.
Keep in mind, as your CHT's come down due to timing, expect your EGT's to go up.
One last note, if your timing is correct for your engine (regardless of the make of ignition installed) and your CHT's are still higher than you like, check your baffles and seal any air leaks you can locate.
Due to some of the comments on this site regarding high CHT's, I decided to play with the timing on my engine.
The parallel valve 8.5:1 compression O-360's standard magneto timing is 25 degrees Before Top Dead Center (BTDC). (This is basically the default timing for most parallel valve engines, check your manual for the timing for your engine and don't take my word for this!)
The P-mags have two basic settings, called the "A" and the "B" curve.
The P-mags have a six wire electrical connector that is used to attach the ground wire (Pin 1), positive (Pin 5) and negative (Pin 4) power leads, tach signal (Pin 6), and two connectors to provide serial send and receive signals (Pins 2 & 3).
There are five ways to adjust the timing on the P-mags.
1. Add a jumper between pins 2 & 3. No jumper and you are running on the "B" curve. Put a jumper in and you run on the "A" curve.
2. Modify the "B" curve using the EICAD program provided on the Emag website.
3. Manually set Top Dead Center off a few degrees
4. Install an EICommander and use that to manage (and monitor) your P-mags.
5. Develop your own management tool.
Since I just happen to have an EICommander installed in my plane, I will go with option #4. (Full disclosure: I am one of the principles involved with the development and marketing of the EICommander.)
A little definition here, the "A" curve (Jumper in) starts at around 26 degrees BTDC and allows the engine to advance to close to 30 degrees. The "B" curve (Jumper out) starts at close to 29 degrees and allows for an advance close to 34 degrees.
Since a number of people wrongly believe that if they run on the more advanced "B" curve they will get more power, I decided to try flying my plane on the "B" curve. With the EICommander, switching between the two curves or creating a custom one is only a few key punches away. (I prefer the term "configuration" over "curve" since you really aren't changing the curve, only shifting where you run on a pre-defined curve but for simplicity, we will call them all "curves".)
While running the engine on the "B" Curve (Jumper out), I was surprised to find my CHT's running right around 400 degrees F (+/- 5*F) and using a lot of fuel to keep them cool. Climbs were a challenge because I had to keep my airspeed up to keep the CHT's under control.
After two flights with this setting I went back to the "A" curve (Jumper in) and my CHT's immediately dropped 20 to 30 degrees F with no noticeable change in performance. There might have been a change but it would probably take a dyno to measure it.
Now the reason for this post. If you are experiencing higher than desired CHT's, check to make sure the timing of your ignition matches the recommendation of your engine manufacture.
While my timing was only off 5 degrees, the CHT difference surprised me.
If you have an angle valve engine, chances are your timing should be 20 degrees BTDC. (Check your manual!) If you are running P-mags without the jumper installed, you are running 10 degrees off and may not be doing yourself any favors. Even with the jumper in, you are still five degrees off.
I strongly suggest you download the EICAD program, connect a PC to each of your P-mags, and add a negative shift to get the timing down where it belongs.
If you have a parallel valve engine that requires 25 degrees BTDC timing and are running P-mags, put the jumper in.
The advance limits are only used at lower power settings and shouldn't be an issue.
Your cylinders will thank you for the lower temps and you might just pick up some additional performance.
Keep in mind, as your CHT's come down due to timing, expect your EGT's to go up.
One last note, if your timing is correct for your engine (regardless of the make of ignition installed) and your CHT's are still higher than you like, check your baffles and seal any air leaks you can locate.
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