Proper Engine Timing

[N941WR]

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.

[RV10inOz]

Bill, great post.

If I can also add that when compared to the traditional magneto, most EI's still give you spark advance, as the 25DBTDC magneto fires the plug somewhat after this and it varies depending on load. Until you see this on a fully instrumented dyno it is hard to appreciate but I have seen hours and hours of it to tell you it is real.

As a rough guess the typical IO360/540 is a couple of degrees, and on the big old Chieftan it is several more depending on which magnetos are fitted. Lycoming never knew this when they made the change and it has significant affects.

You are quite correct with the advance and HP gain myth, that OWT takes some killing indeed. I noted that Dan Horton recently discovered this with his article on the 540 test a BPE. It often reduces HP and the other OWT is that the CHT is higher due to more energy being extracted from the fuel.

So while I endorse your posting above can I add that being mindful of spark lag is something to keep in mind. And yes the cylinders will love the lower temps but also lower peak ICP.

Good work

[N941WR]

David,

While developing the EICommander we built a test rig so we can spin two P-mags at the same time. We did this so we can test the Timing Divergence Alarm feature of the EIC. (This feature alarms when the difference in firing between two P-mags is greater than 2 degrees.)

Initially we used Lycoming timing gears, including a crank gear and a very accurate/stable electric motor to spin both P-mags.

We were surprised to find the the gear train produced so much noise you couldn't stand next to it when running at typical flight RPM's.

The second thing we found was that the gear lash inherent in the design allows for as much as 1.5 +/- degrees variation in timing while the engine is running and that was with new gears.

(We switched to a cogged belt and pulleys on our test rig.)

[TrueAirSpeed]

Thanks Bill!

[RV10inOz]

Indeed Bill, that and crankshaft torsion and all manner of variables moving around, and typically as you measured 1.5-3 degrees of Static timing to actual spark is not unusual.

So as rough number if you want the EI to fire the plug at the same time the magneto would set it to about 23 degrees or on a high compression about 18. Its as good a guess as you will get. Some of the gear driven EI's might still have some backlash so they would need less than say a flywheel sensor which is damned near instantaneous.

Cheers!

[N941WR]

Originally Posted by RV10inOz

...
So as rough number if you want the EI to fire the plug at the same time the magneto would set it to about 23 degrees or on a high compression about 18. Its as good a guess as you will get. Some of the gear driven EI's might still have some backlash so they would need less than say a flywheel sensor which is damned near instantaneous.

Cheers!

You are exactly right! A flywheel sensor, such as what Light Speed provides an exact firing angle, every time. The downside to that setup is that you need a pickup mounted behind the flywheel and wires running to some type of "brain box" and I've seen these wires cut, pickups vibrate off, etc. Bummer our engines don't have a Crank Angle Sensor built into them like most car engines now have.

That is one thing I like about the EICommander is that you can adjust the timing in flight in 1.4 degree increments.

The thing that saves our engines is that they are relatively slow turning monsters with very large flame fronts. If you had that kind of timing variance in an F1 engine it would melt itself. Same goes for a Honda S2000 engine or any of the current batch of turbo engines.

[N427EF]

For the life of me I can't understand why anybody is bothering with magneto type technology. Most have a rap sheet a half mile long and need frequent and constant attention to keep the engine running.

You are exactly right! A flywheel sensor, such as what Light Speed provides an exact firing angle, every time.

The thing that saves our engines is that they are relatively slow turning monsters with very large flame fronts. If you had that kind of timing variance in an F1 engine it would melt itself.

It seems to me that we are constantly relying on the relative forgiving nature of our Lycoming engines to have substandard accessories drive essential functions to keep these engines running.

Lighspeed EI has been around for 25 plus years, winning races in Reno year after year, establishing xcountry speed and distance records and and generally proven itself to be a superior alternative to antiquated magneto technology.
The downside mentioned of wiring behind the flywheel and some kind of black box, seems like things I heard my grandfather utter when he first saw a television set.
The inherent inaccuracies of gear lash and mechanical tolerances that produce
the less than perfect firing intervals are long burried in the automotive world and yet we still try to improve the horse carriage .

While I am too grappling with a magneto and the associated AD on the impulse coupling I am seriously considering chucking that mag for a second EI.
25 years and literally thousands of flying airplanes with Lighspeed EI is prove enough
that EI works better than a set of mags. You set it once and you are done with it.

[RV10inOz]

I can show you 2 (TWO) double EI flame outs. Two different brands and two different styles. No names OK!

One unfortunately made the newspapers, the other did not. The second one was averting disaster due to just enough distance back to a major airport and subsequent well above average stick and rudder skills to avoid bent metal. This pilot is an ag pilot and like most of them above average skills close to the ground. This was not a single point of failure, this was two separate EI's that failed within 1-30 seconds of each other, and the first one had him turning around to the field and the second one went shortly after.

The former one was a victim of what Bill has mentioned.

The downside to that setup is that you need a pickup mounted behind the flywheel and wires running to some type of "brain box" and I've seen these wires cut, pickups vibrate off, etc.

Read this link and look at the photos. i knew these two guys, one better than the other. I take this stuff seriously, and while Ernst and I are friends, this is why I disagree with him on this topic.
http://www.abc.net.au/news/2013-12-0...ndakot/5145204



I am not saying that two mags could not fail at the same time either. In fact some of the single drive ones have a common point, but overall the history of Magneto's still has a record that is hard to beat. If one is very honest with the number of posts and threads here about EI problems plus all the ones that do not get reported the number might not be that good in comparison. In my relatively short GA history, the ratio of mags to EI's is a large number, and the ratio of problems is the inverse.

YMMV folks, and no doubt some have had good long histories, but that is not guaranteeing others do not.

[N941WR]

Please try not to make this a brand X vs. brand Y argument. There are plenty of those threads out there already.

The point of this thread is to discuss the impact of timing on CHT's. The type of ignition or how you set the timing is secondary.

Like David (RV10inOz), I went out of my way not to mention any specific ignition other than the one used for test, as described in my original post.

[Joe]

Originally Posted by N941WR

If you have a parallel valve engine that requires 25 degrees BTDC timing and are running P-mags, put the jumper in.

I had a conversation with Brad Dement of EMagAir on this topic before first flight (more than a year/130 hours ago) because I was concerned about kickback during starting and also best economy at low power settings.

Unless I misinterpreted or mis-remembered, I believe he suggested I could have the best of both worlds by using the "B" curve (no jumper) but timing the PMags at about 3 degrees past TDC instead of TDC. Could you address this concept please?

My experience with this setup has been high CHTs with extra fuel necessary for cooling at high power settings. But economy has been excellent at high altitude/low power settings.

My equipment: YIO-360-M1B, dual 114-series PMags, Hartzell CS prop.

Thanks,
Joe