I have a copy of an engine emissions test report that NASA performed for the EPA in 1976.(report TM X-73500) They studied a 160 HP Lycoming engine extensively to see what effects humidity, air temperature, fuel mixture, and ignition timing had on emissions. A by product of the study was a 206 page volume of fuel consumption and horsepower statistics. While the focus was on emissions, they gathered extensive data on BSFC and HP under a wide range of conditions.
here is a Dropbox link.
https://www.dropbox.com/s/dd2ywydyq0loy3d/LycomingO320NASA.pdf
Interestingly, while there are performance losses when timing is retarded from spec, there are little or no gains when advancing the timing beyond spec. They basically confirmed that 25 BTDC was ideal for that engine. Advancing the timing to 30 BTDC had virtually no benefit.
Retarding the timing to 20 degrees cut HP from 157, down to 148. Advancing it to 30 degrees only raised it from 156, to 157.
The main thing to take from this, is that keeping ignition timing precisely at the specification is more important that most people realize. That means maintaining the ignition system with a focus on the timing event inside the magneto, and from the magneto to the engine. Internal timing is important to achieve the dwell time needed for coil saturation and optimum spark output. Optimum spark is both high voltage and long duration. External timing puts the spark to the plug at the correct moment. Most mechanics do not understand the difference in these two events. It's poor maintenance that causes poor performance, not necessarily the fact that the magnetos have a fixed timing event or are 1930's tractor technology.
I suspect that the majority of magneto-equipped engines with more than 500 hours on them have incorrect timing. Even when the external timing is set correctly, the internal timing can be off several degrees, resulting in loss of performance. Combine this with poor quality spark plugs like Champion massive electrode plugs, and you can be losing 10-15 HP. Add in carburetor heat leaks, poor cylinder baffling, and fuel system discrepancies, and you create a real dog.
Controlling the engine fuel mixture and timing with a closed-loop electronic control system is the way to achieve the best performance. We're probably farther from that goal than ever, since the Aerosance FADEC seems to have gone nowhere since 1998.
The best combination of conventional ignition system components at the moment are Bendix magnetos with Tempest fine wire plugs. Tight plug gaps are critical and these hold the gap exceptionally well while allowing maximum spark exposure to the fuel air mixture.
It will be interesting to see how Electroair fares compared to the LASAR system that failed in the market place. Maintenance was part of that, because parts were ridiculously expensive and sometimes unobtainable.
Buried in the Electroair STC Instructions for Continued Airworthiness: Every 1000 hours or 5 years, replace the ignition harness. It can't be deferred because as an STC ICA it is an Airworthiness Limitation. Any idea what that will cost? They could set the price at $1000 and you could choose to buy it, or ground the plane.
This system uses two different timing curves and adds them based on conditions. An RPM curve, with a max of 26.5 degrees at 2700 RPM.. And a vacuum curve, with a maximum of 18.5 degrees at 16" MP. They are added together, but there are no conditions under which you could get all 45 degrees of advance. Under typical conditions you may get 28 total. You would have to be at 16"MP and 2700 RPM to get all available advance. It drops off steeply after that.
If you apply the EIS timing curve to a typical Lycoming performance cruise power setting of 24" MP and 2400 RPM, you get ZERO vacuum advance, and only 24 degrees BTDC because you have yet to hit 2500 RPM, where the RPM advance curve equals the OEM timing setting of 25 BTDC. To get any benefit from the vacuum advance curve, you have to be below 75 percent power. It appears that settings of 55 to 65 percent power will allow total advance to equal or exceed the OEM setting of 25 BTDC.
At 22"MP and 2300 RPM, you get 23 BTDC rpm advance plus 4.5D for a total of 27.5 BTDC timing. If you go to 23/2300, you get 24+2.25 for 26.25 BTDC total timing. Some Comamche 250/260 pilots use 22"MP/2100 RPM cruise setting, giving 22 degrees RPM + 4.5 vacuum advance for 26.5 total timing. That's a whopping 1.5 degrees advance, which NASA says gives you a .0064% HP increase. If you go over square, you lose the vacuum advance and are back to 24 BTDC, so you LOSE a degree of timing. Oversquare settings like 24/2300 and 23/2200 are known to produce good performance, long top cylinder life, and lower vibration. Using them essentially cancels the vacuum portion of the EIS timing advance, and with good reason but without thinking this all the way through. As cylinder BMEP rises under high MP and lower RPM combinations, the chance of detonation increases. The simplest way to avoid this is to retard timing under those specific conditions, or to find the happy medium under all conditions. That happy medium is the OEM advance setting. But this system appears to retard the timing below the OEM setting in many cases, unnecessarily. This might be beneficial to high compression or turbo engines that need more detonation margin or want the ability to operate on lower octane fuel. But typical Lycomings only need 91 octane and so the detonation margin with 100LL is huge. And don't forget as currently configured, this system gives ZERO vacuum advance above 24"MP. So it is useless on a turbo.
The highest amount of advance will occur under high RPM and low MP conditions. For example, at 10,000 feet you might have 20" MP and 2500 RPM. Under these conditions you will get 34 BTDC total timing. This is where you should see the maximum benefit. Low MP high RPM cruise flight above 8000 feet. The least amount of advance, sometimes LESS than OEM, will occur during high MP conditions such as takeoff and climb. This is according to the Electroair charts:
http://www.aircraftspruce.com/catalog/eppages/electroair.php
The numbers I have seen posted don't appear to be any better than book performance numbers for a new plane. It appears that most of these retrofits are on 30-50 year old planes that were driven by upcoming repairs or dissatisfaction with constantly throwing money at old problems. So we may simply be seeing "performance improvements" that would come from stock new replacement parts, installed by competent mechanics. For example, I flew a completely stock B model Twin Comanche for years that would true at 170 KTAS at 9000 feet on 15.4 GPH. No speed mods whatsoever, and actually had poor paint and some other drag inducing items costing a few knots I'm certain. But good engine maintenance made it efficient in spite of the aerodynamic challenges.
I'll wait to see how this evolves before jumping in. A better timing curve is needed IMHO. At the moment I see no benefit for the substantial outlay on my twin, or for my customers.
NOTE: In the EA info pages is a note about cylinder Peak Pressure occurring at 11 degrees ATDC. I'm not sure if this is an error or intentional, but all data I have seen indicates optimum PP occurs in a band from 14 to 18 degrees ATDC and it is linked to ignition timing. If PP occurs too soon the engine will be prone to detonation. If too late, it runs hot and loses power.
