operation on one mag - effect on temps

I inadvertently did a 20min flight on only the right ignition today (I have Elect ign on right, and a mag on the left). I didn't notice until I landed. However, I did notice my CHTS through the whole flight were significantly lower (about 30 degrees cooler). Othert temps were about typical. Is this to be expected running on only one ignition, or could it signify a timing issue with my left mag that makes the CHTs run so much hotter when I'm on both ignitions?

I'll take a stab it this. Running on one Mag is like running a more retarded ignition. It should give you a higher EGT than normal (fuel closer to still burning as it leaves). It might give a lower CHT due to less power output, but I don't know for sure. You didn't ask, but I doubt any harm was done.

-Andy

The facts

When you operate on one mag, the flame front travels at the same speed but it has more fuel and air to ignite from the one source.

This results in a delayed peak pressure, thus ThetaPP is later after TDC and the peak pressure will be lower as a result.

As you have a lesser pressure to begin with when released to atmosphere, there is a lesser pressure drop and also a lesser temperature drop. This means you see a higher EGT.

As you have a lower peak pressure, you have have less heat transfer to the cylinder head due to a thicker boundary layer. This means lower CHT.

There is the same amount of energy (fuel) but the peak pressure occurring much later means greater than the optimal ThetaPP and thus less torque produced. There is an optimal range for ThetaPP and this is why despite what people think, continual advancing of the spark event does not generate more power as some people think it does with a fixed speed engine.

I have the same thing. One other thing I noticed is that when shutting down the Slick the CHT's do drop and the EGT's go up just like is being discussed. When turning the Slick back on, they all go back to where they were.

However, when shutting off the P-mag and running on only the Slick, the CHT's stay just where they were. I've checked the timing several times on the Slick and the P-Mag and all is good.

My question is, why would the CHT's drop when the Slick is off but not when the P-Mag is off?

Paul, The chances are this is the other way around. Turning the PMAG off should drop the CHT and rise the EGT.

Think about it for a minute as to what the science says should happen. I reckon you are confusing yourself?..which is easy to do?just ask me

Actually David, shutting off the Slick does drop the CHT's. I thought the same as you said, but it's NOT that way. That's what is so puzzling. And like I said, when running only on the Slick, they stay at the higher reading.


My intention is to put another P-Mag on when I save up the money, but I sure would like to figure it out before.

I would like to see the data file for that.

I reckon you are switching the other way around. Where is the magneto timed to?

David,
Next time I get out and fly, I'll get a data log for you.

I thought the same thing, (switched backwards), but that's not it. Been checked numerous times. Timing on the mag is at 25. The mag is firing the bottom plugs and the P-mag the top ones. It runs really smooth on the P-mag alone with very little RPM drop with the Slick turned off. On the other hand when turning the P-Mag off, the drop off is around 50-75. It's had me baffled for quite some time.

At any rate, I'll get a data download from the Dynon and get back to you.

Thanks