Plugs, P-Mags and CHT's

[mike newall]

So,

We completed our RV7 - 3 years ago, dual P-Mags, very happy with the service and performance, however.......

CHT's were high from the get go.

We have an ECI IO-360 180hp parallel valve motor made with care, love and attention by Mattituck - Thank you Mahlon.....

Running NGK BR9EIX on top and Unison UREM40E on the bottom, both harnesses made up and tested by me.

CHT's were in the 400's on climb and when stunting.

In the cruise, lean of peak, they would drop to 370f.

Did a LOP balance check in accordance with Mahlon's instructions.

Also, big split on EGT's when taxiing. 1 & 3, lower than 2 & 4 by a good margin.

It has a plenum which is well sealed, we have a little ventilation down the back as per recent threads.

That is the background - hope I haven't left anything out Dan

Now...

We did this year's annual and changed the bottom plugs to NGK's with new harnesses provided by Brad.

OMG.

CHT's down by 30f.

EGT's stable and even.

My flying buddy races motorcycles and before raced big V8 stock cars. He and his Bro are wizards at auto tuning etc etc and the are interested.

Unfortunately, we changed two parameters at once, so I can't say it was the plugs, the leads, or both.

What we do know is that we are most happy with the new set up and if we get any plug fouling it will be..... Oh Really.... O'Reilly's - 8 NGK's please !

Much better than Autozone - super nice chaps at O'Reilly's, especially on OBT in Orlando.

I have no idea why just changing the Unison plugs and leads made a difference, but it did.

I will stand back and listen to the input from the great and the good.

[RV10inOz]

I suspect you changed something else.

Under exactly the same conditions in flight, the only thing spark related that will change the CHT is Peak ICP and the Theta PP.

If you can explain how the aviation plug and harness was somehow sparking off about 2 degrees earlier, I want to know about it.

Did you do an annual inspection of the PMAG as I think you are meant to do and retime them?

The laws of physics are at threat here

[N941WR]

David may be on to something.

How are you timing your P-mags?

We have had EICommander customers who will use the "Blow in the tube method" to time their P-mags, only they do it one at a time. For some reason, that we can't explain, the ignitions take a different set when compared to timing them together with the same puff of air.

The few degrees difference is enough to produce a Timing Divergence Alarm. More likely a warning than a full alarm.

[Edit]
Just to be clear, we recommend using the "Blow in the tube method" to time P-mags but we believe it is best if the MAP lines are tied together and the timing is set with the same puff of air.

[RV10inOz]

Thanks Bill,

And just like a conventional magneto, the timing position must be achieved by rotation of all the mechanical items in the one direction....that of operation so that the timing gear is driven in the same position. No going backwards.

[N941WR]

Originally Posted by RV10inOz

Thanks Bill,

And just like a conventional magneto, the timing position must be achieved by rotation of all the mechanical items in the one direction....that of operation so that the timing gear is driven in the same position. No going backwards.

Correct. This can't be stressed enough!

What I found odd about the customers who were setting their P-mag timing one at a time was they insisted they did not move anything between blowing in the tube for one P-mag and the other. They may have backed up the prop to set the timing and one could have been off slightly; we will never know for sure.

[mike newall]

Hi Gents.

Bill - my EICommander is sat in our currently under build RV8 - Brad and I had a long chat at Sun n Fun, then I contacted you and ordered one, so it can't help me here just yet !

The sequence was thus.

Damaged a starter with kickback, so it went for overhaul.

Called Brad about re programming the P-Mags to set start delay but we are all Mac users with no W*ndows machines anywhere. He then suggested resetting the timing to 3? after TDC and to use the standard blow timing method. That was done BEFORE we swapped the plugs and no discernible difference was noted. They were timed one at a time with no movement between timing at all.

At the annual, we already had the new leads, reducers and plugs in stock so Mark swapped them all over but didn't touch the timing.

Now we notice this improvement and quite frankly, we are stumped. Apart from taking the plenum off and putting it back the same we have changed nothing FWF.

Also, with the smoothing out of the idle EGT's, we presumed it had to be either induction or ignition related. Nothing was changed on the induction, so presumed the extra spark on the NGK's was giving better combustion.

I've been reading Mike's articles about LOP running and flame propagation in the EAA mag recently which made me think it was ignition related.

Anyhow, we are pleased with the results and we will see if they hold out after a while.

[Weasel]

I suggest a quick easy test. Re-install the old plugs and wires and go fly again. Double check to see it that was accutally the change.

[Mike S]

Originally Posted by RV10inOz

I suspect you changed something else.

Under exactly the same conditions in flight, the only thing spark related that will change the CHT is Peak ICP and the Theta PP.


The laws of physics are at threat here

The something else he changed was the spark plug gap.

And, possibly the voltage/energy available to jump the larger gap----and the duration of the spark.

My guess is that the new setup is a lot more efficient at lighting off the mixture in the cylinders.

Laws of physics are safe

[Bavafa]

Originally Posted by Mike S

The something else he changed was the spark plug gap.

And, possibly the voltage/energy available to jump the larger gap----and the duration of the spark.

My guess is that the new setup is a lot more efficient at lighting off the mixture in the cylinders.

Laws of physics are safe

Wouldn't any of this causes a higher CHT? Better/hotter spark will create more power, more energy thus hotter CHT, right?

Are you seeing better numbers (airspeed) for the same power settings?