Secondary Ignition Timing

[bvolcko38]

I used a timing light to time my secondary ignition. I made a paint mark on the flywheel using the primary ignition at 20 degree BTDC. I matched that to the secondary. All seems good. Kerry said I shouldn't do it, but didn't give a reason why. Thoughts?

[mike.smith]

The basic reason not to use a timing light is that it does not work at low RPMs for the engine. Timing is markedly different between low and high RPMs. Anyone who has a tuned VW can see this by switching mags on the ground during the mag check, and observing the RPM drop. When you do the same thing at high cruise RPMs you will not see the same drop.

You can read up some yourself and make your own decision:
viewtopic.php?f=7&t=1318&p=10959&hilit=timing+light#p10959
viewtopic.php?f=7&t=1992#p14802
http://www.sonex604.com/timing.html
http://www.eaavideo.org/detail/video/34 ... Start=true

It's also pretty tight between the wing and a spinning prop on a Sonex, so not exactly the safest place to be.

[Darick]

I just checked my timing in the air yesterday and was very happy with the results. On the ground I typically read 75-100 difference. It's always hard to pin down an exact rpm because it jumps around about 20 -30 rpm on the MGL E1. So flying at 3000 RPM, 2400 altitude, 110 mph indicated, 4.9 fuel burn,here's my results...
BOTH ignitions EGT 1025, 971...CHT 316,255...RPM 3000
PRIMARY. EGT 1112, 1076...CHT 309,249... RPM 2880
BACK TO BOTH FOR A CHECK...EGT 1031,1000...CHT 314,253...RPM 3000
SECONDARY. EGT 1023,996...CHT 312,249. RPM 3000.

I'm happy with these numbers and won't change anything. Engine time 10 hours. Any comments are welcome.

[sonex1374]

Darrick,

Looking at your numbers, things look pretty good. CHTs are in check, and the rpm difference between the mags (primary) and electronic ignition (secondary) is relatively small (100 rpm). A few things come to mind.

The electronic ignition is likely advanced (respective to the fixed mag timing). When you switch from both to elec ignition there is very little change in rpm or temps, indicating that the elec ig is doing most of the work lighting the fire (the mags are firing later when the combustion event has already started).

When you switch to mags-only, the timing is slightly retarded from the elec ig and the engine is making less power (less rpm, and higher EGT from more waste energy going out the exhaust; lower CHTs because power is reduced all around).

Running your engine with advanced timing is a way to get better power and extract more of the energy from the fuel (e.g. efficiency). There are limits however, and the CHTs are the primary indicator if you are approaching them (CHTs will rise dramatically when the timing is too far advanced). If your engine is running well and CHTs are good, then the timing (whatever it is) is probably OK. Should you notice that CHTs are running higher than desired and switching to mags-only brings CHTs down, then you might conclude that timing needs to be retarded some. In any case, I think you're good where you are.

Jeff

[Darick]

Thanks Jeff for the explanation, it makes sense. I was not able to explain why the numbers were like that. I like the idea of more power but I also understand too advanced is also a reason for detonation and/or pre-ignition.

On climb out (3300 rpm) I have to reduce throttle to 3000 and flatten the climb to avoid quickly rising CHT on the hottest cylinder. When it starts to get over 400/405, just a few hundred feet off the ground, I lower RPM and flatten climb. It may peak at 415 before cooling back down. I don't like that and was justifying it because it only has ten hours.

I'm way cautious about these things (haven't been out of the pattern yet!) and after your explanation I NOW want to RETARD the secondary. On the other hand, (this would be a good discussion point) having the ability of a little more power on climb out would be desirable, then just run on primary the majority of the time. Now the question is, just how much more power does advanced timing give you? If negligible, then retard it and avoid ANY possibility of detonation or pre-ignition. After all we don't want to have the ignition event occur when the piston is still traveling up.

When adjusting the timing, how many degrees would you move it at one time, <5? >5?. Any ideas are greatly appreciated!!!

Thanks for the analysis! This forum AND the podcasts are super helpful!
Darick

[bakerde36]

Hi Darick,
This is a little of subject but wanted to know if you could tell me your set up config for the RPM on the E1
I can't keep mine from jumping 0-4oo rpm constantly. I have mag for primary and motorcycle ignition for secondary which may be totally different. Thanks Densil

[sonex1374]

Darrick,

Your engine at 10 hrs will still be tight, and running hot. My advice is to continue doing what you're doing on climb out to prevent it from getting too hot, but just know that the temps will improve over time as the engine breaks in fully. Remember that Sonex has set the CHT limits based on decades of use, and they're good limits. 420 deg F for 5 minutes doesn't mean you should add your own safety factor on top of it, and start worrying at 410 for 1 minute. Like Kerry says, "Green is green!". Once you get some more time on it you can continue to refine things, but for now, I think you're OK.

The ignition timing was chosen at 28 deg by Sonex as the best overall compromise of power, efficiency, starting and detonation margin. Other VW conversions use different settings and think that's a better choice all around. It's hard to say who is right, or that a single answer even is right. Modern computer controlled ignition is constantly being adjusted in an attempt to get the best balance of factors at that particular moment. We aren't so lucky with our fixed timing systems. Having said that, your *slightly advanced* elec ign is probably fine as-is, but if you retard it to match the mag timing exactly that's not a bad thing either.

The CHTs in flight will tell you if your timing is too advanced, so on your next flight try another test. Set up in cruise, let things stabilize for a couple minutes, and then turn off the electronic ignition. If the CHTs go down dramatically, retard the timing slightly. If they only change a little, then you're good, and probably enjoying the benefits of the more advanced timing setting. Next, conduct a takeoff but shortly after leaving the ground (like at 200-300 ft) turn off the electronic ignition and note the CHTs on climb out. Compare them to the previous takeoff & climb out (that was conducted with both ignitions on). Again, if CHT's go down significantly, then you should retard the timing some (ideally in very small 1 or 2 deg increments). If not, then you're good.

The timing setting you choose depends on what you are asking of your engine. For WOT takeoff and climb out, a retarded setting improves the detonation margin and engine cooling. At cruise an advanced setting improves speed and efficiency. You could always take off using only the (retarded) mags, and then cruise on only the (advanced) elec ig, but essentially you then only have a single (non-redundant) ignition system, one that you toggle between two settings but never use at the same time. Getting both systems close to each other still gives you the redundancy and just a touch of flexibility.

Jeff

[Darick]

Hi Darick,
This is a little of subject but wanted to know if you could tell me your set up config for the RPM on the E1
I can't keep mine from jumping 0-4oo rpm constantly. I have mag for primary and motorcycle ignition for secondary which may be totally different. Thanks Densil

I'll get back to you on that...may have to go to the hangar to get that info...

[Rynoth]

Jeff, that information is gold, thank you.

[Darick]

Hi Darick,
This is a little of subject but wanted to know if you could tell me your set up config for the RPM on the E1
I can't keep mine from jumping 0-4oo rpm constantly. I have mag for primary and motorcycle ignition for secondary which may be totally different. Thanks Densil

Here's my set up. The first option which is not shown, is SCALE, which I have set to 4000.