Magneto timing on IO-360

[Antoine]

I have been working on aerodynamic tweaks lately and was quite successful.
My plane did 145-146 KTAS on 9 GPH at 9000 ft.
Since the goal was to maximize efficiency I also started toying with LOP operations and got 138-140 KTAS LOP under 8 GPH, but I was not happy with the smoothness. The engine felt like it was ready to choke...

Also, the engine did not seem to deliver any extra power past 2600 RPM.
The plane was not faster at 2700 than at 2600. I am certain that this was not the case in the past.

During the last 50 hours I had magneto timing checked and found both magnetos set at 27 degrees.
I had them reset to precisely 25.

Much to my disappointment, it seems that the plane is no longer as fast. I am not sure why (it could be the magnetos but it could also well be the summertime and higher temps)
The plane has fallen back into its usual 140-142 KTAS on 9 GPH. And it is no longer happy at 9 GPH (seems to want 9.3 GPH where 9 was perfect before). This also did not fix the lack of extra power at 2700 RPM

(and since I was busy getting the speed back, I did not do any LOP tests so I dont know if this bought me better LOP operations).

I fly high and always cruise WOT, mostly 2400-2500 RPM except on long trips where I am willing to exchange speed for economy.
at 9000 feet, the plane typically wanted 9 GPH for peak EGT, now it is more like 9.3 GPH for it to sound happy.

(apart from that the engine is very nice and there is absolutely nothing wrong with it).

What do you think?

Would it make sense to revert back to 27 degrees? Where do I find guidance on non-standard magneto timing?

[rwtucker]

Like you, Antoine, I'm not an A&P and most of my experiences come from a close working relationship with my engine and conversations with the high performance guys around here who modify these engines. Several of these pilots race at Reno.

My understanding is that when you go above 25 degrees, you enter the realm of the experimental. Other things being equal, higher timing (e.g., 25 vs 20) gets you more performance, higher CHTs, better (or easier) LOP, higher octane requirements, and greater possibility of pre-ignition.

At 27 degrees, I have found a few LOP sweet spots. One is a 128-132 kt cruise at 5.9 GPH, which is nice for a frequent short run I make where full speed ROP would change my in-air time by only a few minutes. At this setting, my CHTs are all below 300 and EGTs are around 1525-50. Just for fun, I'm experimenting with another LOP setting at 2450 RPM to see if can take advantage of the tuned exhaust. I know that some other DAN members have recommended that. All of my LOP settings are reasonably smooth, although the engine does "feel" different.

LOP is very different on my other 360 (a turbocharged Continental). I can enter it in almost any configuration without any roughness.

From what I have been told, this discussion would go away if we were permitted to use electronic ignitions on both sides.

[Antoine]

Thank you Robert.

Interesting that yours is at 27 degrees. If you are flying relatively high, I think this is not a bad idea.
I did not know that more ignition advance was actually better for LOP!

Next annual (very soon) I will revert back to 27 and see what happens.
The CAFE papers about electronic ignition give a good explanation of ignition timing vs altitude.

[rwtucker]

I did not know that more ignition advance was actually better for LOP! Next annual (very soon) I will revert back to 27 and see what happens. The CAFE papers about electronic ignition give a good explanation of ignition timing vs altitude.

The experts around here seem to disagree on this point but the mechanic in charge of my engine believes it works better on the M1A. Keep us posted. Since you have been tracking LOP behavior, yours will be a good test.

[Steve]

The other thing is that it is difficult to get a stable Mag timing setting on the IO360. What you set as 25 degrees today may be 27 degrees tomorrow. There is a lot of slop in the accessory case gear train, which affects the stability of the Mag timing. I check mine every time the cowl is off, but don't try to adjust if it is a degree or so off...

Steve

[Antoine]

Annual is end of october and I will have it checked and set back to 27. Will report early november...

[Antoine]

Some time ago, Colin told us he would PIREP on the Electro-Air install. I am still toying with this idea.
If it can really save 1 GPH at altitude, this is a terrific product. Customer testimonials on their web site (including one DA40) seem to support this.

[rwtucker]

I'm interested too. My plan is to add one instead of the first magneto that needs rebuilding. Maybe the FAA will let those of us on this side of the pond go full electronic as part of the revised rules that they are behind in developing. What does it look like on your side Antoine?

Looks like the price jumped. Didn't these used to be in the $2,400 range?

[Antoine]

Yes the price is now $3400 plus install and this is not so simple: drill though firewall...
Since my plane is N-Reg I am also under FAA jurisdiction. If they ever allow full electronic, we'll need to make the battery / alternator fault tolerant as otherwise the engine would die in case of a failure. It is feasible, but I guess very costly in a DA40

Another reason for holding our guns is that I believe EI would be much less useful in a supercharged plane (higher MAP does not justify a drastic change in the timing).
Is this reasoning correct?

[Lance Murray]

Antoine,

Do you have the Basic Theory of Operation Wright R-3350 1957 manual?

http://www.advancedpilot.com/store.html

This book is the bible on ignition timing and LOP operation. It explains exactly what is going on in regards to timing and LOP operating.

This link references the manual.
http://www.gami.com/articles/bttfpart1.php

FYI. I recently had an IO-360 built for my Pitts that I plan to race at Reno. The timing is set at 20 degrees. I am not exactly sure of why and I will try to find my manual to investigate this. The engine has 9.5:1 pistons and is planed to run at high RPM around 3300.