[Paul K]

I am running an IO-360, 8.5:1 cylinders, dual P-mags, fuel injection, cold air induction, and a WW200RV prop. I have about 80 hours on it and I feel it is well broken in.

The question is, if I remove the timing jumpers on the mags, what should I expect? Performance change, fuel burn, speed, idle, etc.

For those who have done this, what can you tell me?

 

[RV10inOz]

Break in was achieved about 1/10th the time ago

What should you expect? Higher CHT's. Leave it where it is.

If you ever get to see an aero engine on a really well instrumented dyne like the one at GAMI, you will see what happens to HP with more advance. Depending on where you started, the HP usually drops. Contrary to popular belief.

Apart from the already advancing curves in the EI's, the "Effective Spark Timing" from an EI is a few degrees advanced over a magneto already due to the lag in a magneto.

You really do not need more, and you do not need more CHT.

 

[Toobuilder]

A dyno is at SL however. Lean mixtures in thin air mean a slow flame front, meaning a need for timing advance (compared to "fat" air). While its true that an engine needs what it needs, testing on the dyno isn't likely to tell the whole story.

And I run the Pmags in the "advanced" setting, but for the record have not tried it any other way.

...Guess I should and see what happens.

 

[Paul K]

So standard mag allows advance up to 26 degrees
P-mag A setting, jumper in, allows up to 34 degrees
P-mag B setting, jumper out, allows up to 39 degrees

Controlled by MAP. If I unplug the MAP tubes, it reverts to standard mag 26 degrees or so advance.

Just as a base line, I am a flatlander, field alt 760. Rarely ever go over 12000 and everything is running really good.

Unless I hear a good reason to change things, the jumpers wil stay in.

 

[N941WR]

Typically you will see an increase in CHT's and a decrease in EGT's.

How much depends on your engine and leaning technique.

Give it a try and if you see your CHT's getting too high, push the red knob in. Then, if you don't like the results, put the jumper back in. Better yet, buy and install an EICommander.

 

[RV10inOz]

Typically you will see an increase in CHT's and a decrease in EGT's.

How much depends on your engine and leaning technique.

Give it a try and if you see your CHT's getting too high, push the red knob in. Then, if you don't like the results, put the jumper back in. Better yet, buy and install an EICommander.

You will get a drop in EGT and a rise in CHT. The science says so regardless of your leaning technique.

There is nothing to be gained in higher CHT.

The area under the curve of work in Vs work out is what actually matters and moving the peak pressure to a different angle (Theta PP) and the resulting higher peak pressure is what you get. So higher cylinder pressure, highet temperatures and no gain in HP and maybe a loss??

Tell me why that will be good. These are basically fixed RPM machines thus they do not need the advance like cars do. There is more than enough advance in the standard curve as it is. And remember they fire off earlier due to less mechanical lag than a mag in most cases.

Go try it for yourselves, in your own flying dyno. And by the way you can replicate less or more air in a Dyno, especially one built for the task

 

[miyu1975]

I have dual pmags and still running the A curve. I have been planning to pull the jumper and try out the B curve... I had considered running the jumpers to a switch on my panel. That way I could easily make change any given time..(not during flight).. Is there any benefit in putting in a switch, or do you find once pick a curve you pretty stick to it all the time?

 

[Andy Hill]

After advice from others, I never even bothered with the A curve.

NB at full power, the P-Mag does nothing to the advance - it leaves it where a Mag would be, so as above, "Full Power" is unaffected, as will CHTs at Full power.

At cruise (Higher Alt, reduced MAP / RPM) is where the advance kicks in. You exchange higher CHTs / lower EGTs for improved efficiency / fuel consumption. The B curve to a slightly greater extent than A. If your cruise CHTs are an "issue" then the A curve would seem better, but not an issue for me.

There is nothing to be gained in higher CHT.

The higher CHTs (and lower EGTs) indicate the rather strange concept of burning the fuel in the cylinders to produce power, rather than wasted in the exhaust So I would disagree with you to that extent - the whole idea of EI is to achieve this. Clearly, if the CHTs get anywhere near a limit, you will need to take action to resolve - but my experience is that the P-Mag kicks in at those flight phases where high CHTs are not an issue.

Just my 2cs worth I reckon getting 12%, maybe 15% better fuel consumption over Mags. I am sure my limited understanding will be pointed out by others however

PS

I had considered running the jumpers to a switch on my panel. That way I could easily make change any given time..(not during flight)

The advice to not bother with the A came from someone who did this, albeit he only ran the switch to near enough the oil door to change it prior flight. I suspect after 1 flight on the B curve you will stick to it...

 

[RV10inOz]

I reckon getting 12%, maybe 15% better fuel consumption over Mags.

The comparison was over the A&B curves....not vs Mags.

 

[N941WR]

...Tell me why that will be good. These are basically fixed RPM machines thus they do not need the advance like cars do. There is more than enough advance in the standard curve as it is. And remember they fire off earlier due to less mechanical lag than a mag in most cases....

Keep in mind, that under full power/full load the P-mags act like a standard mag in that they dial the advance back to either 25 or 30 degrees, depending on the curve selected (A vs. B). When cruising at altitude, even at 75%, the timing will advance to the limit set by the curve (or custom programming). For those few people who fly in the teens you can really dial in some additional advance to maximize your power. This works because at high altitudes there is very little air in the mixture and the flame front takes longer to propagate across the cylinder. That's why Clause will run 40* BTC or more on his long cross country flights.

One major advantage of

... I had considered running the jumpers to a switch on my panel. That way I could easily make change any given time..(not during flight).. Is there any benefit in putting in a switch, or do you find once pick a curve you pretty stick to it all the time?

Correction

Note 2: The ignition looks at the jumper state at power-up only. You cannot route
these jumper terminals to a switch and go back and forth between curves while the
engine is running. EICAD does allow you to change timing (Advance Shift) while the
engine is running.

What I said about adding a switch may work with the 114 ignitions but I'm not sure.
I still suggest you bring the wires into the cockpit so you can run their EICAD program or install an EICommander at some later date.

 

[RV10inOz]

When set to the A curve, and configured to spec, on a typical 25 degree engine what is the ACTUAL spark timing?

I would be interested to hear what you think or know.

 

[N941WR]

When set to the A curve, and configured to spec, on a typical 25 degree engine what is the ACTUAL spark timing?

I would be interested to hear what you think or know.

It depends on your RPM and MAP for any particular timing. The A Curve starts at 26* BTC and will go out to 34*BTC. The B Curve simply takes the A Curve and adds 5 degrees. Thus it goes from 31 for high power settings to 39*BTC.

That matches what we see on the EICommander.

 

[RV10inOz]

OK, assuming that is when the sparks go off then, say 26 degrees, not something less. Where do you think the actual spark timing is on a magneto set statically at 25 degrees?



PS, anyone know why two pmags would fail in flight within 15 minutes of each other and the plane had to be towed off the runway. Fortunately it made the airport.

I also hear about low maintenance claims yet another RV7 with 130 hours has oil inside the housing of the light speed unit, and it requires 50 hour inspections?

 

[Walt]

I also hear about low maintenance claims yet another RV7 with 130 hours has oil inside the housing of the light speed unit, and it requires 50 hour inspections?

The lightspeed unit offers both hall effect and direct crank sensor models. The hall effect units have been known to leak a bit of oil into the module, however, the oil does not effect its operation. The direct crank sensor model eliminates this problem and IMO is the preferred option (no moving parts).

 

[gereed75]

I was looking for some advice in this thread http://www.vansairforce.com/community/showthread.php?t=105624&highlight=guru

After 20+ hours, still as described.

By the way, My LSE Hall effect gets a bit of oil in it. It does not effect function per my experience and Klaus's advice.

 

[RV10inOz]

This was the key question......sorry for the drift about the failures.

OK, assuming that is when the sparks go off then, say 26 degrees, not something less. Where do you think the actual spark timing is on a magneto set statically at 25 degrees?

 

[PCHunt]

David, why don't you just supply us with the answer to your question. Then we will all know.

 

[RV10inOz]

Because it is an interesting thought process.

Everyone wants everything as a quick hit answer.....no thinking involved

The answer is it varies a bit but the reality is somewhat less than the static timing. For example the TIO540 Chieftan engine that is timed at 20DBTDC fires the plugs around 14-15 DBTDC. So the lag in the magnet is typically 5 degrees later. And it wanders a bit.

How does this compare to an EI of far greater accuracy and repeatability?

I think this explains a number of things that people observe.

 

[Brantel]

I can tell you another weird thing...

My effective timing changed on my engine when I added the prop governor drive adapter and governor to my engine.

Apparently this had some effect on the lash in the gear train that drives the one mag, one P-Mag combo I have.

The way I noticed it was by how different the drops during mag checks after the prop swap.

 

[N941WR]

I was looking for some advice in this thread http://www.vansairforce.com/community/showthread.php?t=105624&highlight=guru ...

I can't answer as I don't really know how the LSI works. However, with new engines, or recently overhauled engines running P-mags; I recommend the pilot put the jumper in and plug the vacuum advance (or set the max advance at 26*BTC with an EICommander) for the first 10 +/- hours). That way the ignition will act like a standard mag and if you experience high CHT's, it takes the ignition out of the equation.

...Apparently this had some effect on the lash in the gear train that drives the one mag, one P-Mag combo I have.
...

I'm not surprised at all. During the development of the EICommander we found that the valve lash can vary the timing by almost two degrees. That's why the EICommander doesn't start reporting a timing divergence until the difference exceeds two degrees. A little extra drag on the drive train could be the culprit.

For our initial test rig, we cut the back of my O-290 off and spun the center gear with an electric motor. We found the gear noise to be so loud you couldn't stand next to the thing. So we milled up an aluminum plate to hold the P-mags and spin them with a cogged belt. This allows us to very precisely set the RPM and manifold pressure to verify our device works properly. It also allows us to attempt to recreate issues our customers might be experiencing.