By the way: Interesting stories about “weird problems and noises”. I have seen them quite a bit when I was marine engineer. The become even more weird when they resolve themselves. This happened to me (and again with EGT!! It seems to follow me) when I took-off some 10 years ago with the PH-DBO and saw the EGT climb over 1.500 F, while the full power figure normally was 1.400 F. I decided to return to the field, checked everything, found nothing and made no changes and took-off again. Guess what: everything normal again. I still think that I could have been taken-off on just one magneto although I normally very secure on procedures.
Raven and Peter, thank for your comments.
The possibilities you mention both may be very true. As said, it might have been a good idea to check the timing of the magneto’s before removal. On the other hand the “before overhaul” readings that I wish to see, have been there since new and the timing on 25 degrees has been checked on many yearly inspections.
However I indeed have the intention to remove the overhauled magneto again and bring it myself to the workshop and demand to be witnessing the testing and see what comes out. Comparing the both suggestions I think the timing issue will come the closest. During several test runs I also performed magneto checks in cruise (23 / 2330) and both magneto’s exactly showed the same behaviour (rise in EGT while keeping power setting the same).
Removing the Slick mag again may take a while as I have an potential buyer for the Lancair and this may be a third possible solution for the “problem”. Should this not work out then I will probably keep the Lancair thru the summer and I’m also considering to replace one Slick magnet by an electronic ignition such as the e-Mag. Any suggestions with regard to electronic ignitions? Especially while there is only very limited space within the Lancair cowling and it can be hot in there!
Regards,
Dave
The way I approach unexplained changes is by keeping spares and swapping them. Even if nothing changes, I might overhaul the original. I have a spare RSA fuel servo, a spare D3000 magneto, normally I have a spare alternator, two spare autopilot computers, a set of spare servos, a pile of spare avionics, etc. Crazy? For sure! But we are all crazy 
The basic issue is that a lot of faults will never be diagnosed, due to a lack of diagnostic capability / inadequate test procedures. And customer input on anything to specially check tends to be disregarded, either because the customer is assumed to be stupid or because their procedures don’t support it. So e.g. if you send a mag to a mag overhaul shop, telling them it makes a funny noise, they are unlikely to do anything different with it, to look for the noise. They will just throw it onto the mag tester, run it, if it passes it is tagged Serviceable and is by definition perfect.
This is one example. Never 100% for sure tracked down, but I demanded a different magneto returned to me after the overhaul 
This was another example which wasted a lot of my time, but at least was tracked down to a very visible crack. This article shows another aspect of it – a lot of avionics in the extended warranty swap pool are garbage, with intermittent faults.
If you don’t keep spares, it is much harder, because the same part will come back, probably with the same problem, and always tagged Serviceable. Often, this is a business where in the land of the blind the one eyed man is the king.
Then I would guess your old magneto was timed slightly different.
That could be the explanation of the difference you are worried about.
Jojo, Thank you for the figures you are mentioning. They are about the same as I used to see before the magneto overhaul. (EGT 1.350 – 1.400 F, CHT 330 – 350 F, at 23 / 2300 and about 34 ltr. / hour. Of course your LASAR electronic ignition gives a better timed ignition and better spark energy than my good old Slick magneto’s. I think this is exactly the reason why I see different readings after a magneto overhaul. It must have to do with timing or spark intensity, even though the timing adjustment is exactly measured as 25 degrees BTDC. I would not be surprised if I set the timing to 26 degrees or so, the old values would return again. I also wonder why some Lycomings are timed to 28 degrees BFTDC instead of 25 degrees. After all I wish I would have checked the timing before removing the magneto’s.
And again it is in no way the absolute readings of the temperatures (EGT) that keeps me worrying as they are well within limits. It is the sudden change that I see after the overhaul of the magneto. Being a marine engineer in my earlier age, we always considered unexplainable changes on gauge readings after we repaired or adjusted something as the onset for disaster.
To be continued!
On any petrol engine, best SFC (specific fuel consumption – power per fuel flow) is achieved about 25F LOP, but the power curve is pretty flat around that point, so anywhere near there will do.
And anywhere near there the power output will be proportional to the fuel flow.
Peter wrote:
it would not produce a much leaner mixture
Yes, probably you are right but maybe to get just 50F difference you don’t need much leaner mixture – maybe just a little bit leaner…?
I don’t know. Just trying to find a cause.
Maybe just the old magneto before overhaul had slightly different timing?
Carburated aircraft engines have one place where all the fuel enters the intake manifold, for all the cylinders.
Local friends who were too cheap & simplicity oriented to fuel inject their RVs etc. use Ellison carbs which in addition to working upside down are supposed to provide improved mixture distribution between cylinders. My observation is that this provides a lot of opportunity for experimentation with little improvement
My local RV-8 contact can still do something like 140 kts throttled back to 5.5 GPH, 180 kts IAS max and 2000+ fpm climb so he doesn’t care much.
a bit more of air entering the system
I recall, from mucking about with the over-rated K&N filters (for which somebody got a dodgy STC – tested it on an old TB but not the GT model) that a filter v. no filter is worth no more than 1/2" on the MP. So even if you hacksawed the whole air intake assembly off, it would not produce a much leaner mixture
Many of the engines that don’t have that additional data are carburated, and seeing the CHT and EGT mismatch between cylinders on those engines won’t allow you to do anything about it
Yes; I didn’t spot that one. Maybe GAMI will sell you a set of injectors which even it out a bit, for a particular engine model.
Jojo wrote:
you can’t do anything meaningful with just one CHT and one EGT.
Many of the engines that don’t have that additional data are carburated, and seeing the CHT and EGT mismatch between cylinders on those engines won’t allow you to do anything about it. As a result, simply leaning just short of misfire any time you’re below 75% power will get you as close as possible to peak EGT (on the average) without instrumentation on all cylinders. It will thereby provide a useful reduction in fuel consumption on any engine for almost any length of flight, including for engines installed in planes with no CHT or EGT instrumentation at all. Those same planes are typically overcooled by design, meaning you’re unlikely to overheat the cylinders like you would with an injected engine in a tight cowl.
