What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Surefly electronic ignition

And to ask Dan for clarity - with your RV-8 side by side comparison, was the other ship an angle valve like yours?

No, a parallel valve. It should have responded to advance better than an angle valve. An angle valve with a base timing of 28 and a full advance of 38 would even less happy, although I'm sure somebody has tried.

I just flew the RV cross country yesterday with the SDS system replacing the Pmags and can attest that the AV engine responds very differently than the PV (Rocket) I'm used to.

Yeah, that's what the 390 guys have been trying to tell you. For P-Mags, install the jumper, then clock it 5 degrees at installation. For Surefly, I'd set the DIP switches ON-OFF-ON-OFF (22 fixed) or OFF-OFF-OFF-OFF (18 base advancing to perhaps 31 max). SDS and EDIS, program as desired, same timing range.
 
Last edited:
Yep, I actually flew the -8 (angle valve) with the jumper "out", and set to TDC for a few years. It was only after playing with the SDS CPI in the Rocket that I got the slap in the face of reality... When it comes to timing, "more" is not always "better". And the increased CHT is not necessarily because the engine is making "more power"... It might just be eating itself.

Right now I have the CPI set to retard timing on TO and I'm seeing about 17 degrees at my 2600 MSL strip. Yesterday, I took off heavy and in 97 degree heat. I climbed aggressively to 9500 cruise (at first, to clear some Delta airspace), yet never saw more than 360 CHT on my hottest cylinder. Have not seen any cruise performance increase yet, but the retard I have programmed is paying dividends already.
 
I have dual Surefly's on my RV6 powered by a Lycon IO360-EXP with 10:1 pistons. I'm in Granbury, and know the Surefly guys, very well. I don't speak for the comapany, however.

The Surefly was designed to be a magneto replacement for the certified market, that will last the TBO of the engine without maintenance or inspection. The ignition advance keeps the engine well within the detonation margins, similar to the magneto. You will not get advance until the MP gets below appoximately 25". So, WOT, low altitude, the unit will only provide base timing, just as the mag did.

MOGAS was not in the STC because it was not tested. The FAA cannot handle variations, and the fact that auto fuel manufacturers are continually changing their formulas, made testing MOGAS unreasonable. Use MOGAS at your own risk, as you would with any other ignition.

There was a mention of a "blip" during an ignition check. This has been an issue with the Bendix style ignition switches. They will sometimes ground both ignitions as you switch between left and right. This will momentarily reset the Surefly (miliseconds), resulting in the blip. Buying a new switch may not help.

I just returned from a hot summer, high DA trip to Durango, CO and Great Falls, MT. I had good power, but can't compare to the Slick as I never flew the airplane up there on the Slicks. With the airplane heavy, 11,500', 50° LOP, I was cruising at 6.2gph at 155 knots TAS.

I can tell you that most of the "issues" with the Surefly are the result of installation errors, or bad electical/ignition systems:

Not timing at TDC

DIP switches incorrect

Capping the MP line when in fixed timing (MP sensor will through a fault code as the cap will overpressurize the sensor)

Non-compliance with the uninterupted power source requirment. If you wire through a CB or a relay that provides a dirty electrical signal, the unit may not like it. Wire it directly to the battery, per the manual.

Poor grounding of the engine (Surely uses the engine case as a ground)

Bad spark plugs

Bad ignition wires

The list goes on. Most of the units returned, pass bench test. Obviously, there are occasional issues with a unit.

I'm a believer in the company, especially as a witness to what the FAA has put them through. The unit was tested at least 7X more than the competitors.

Anyway, my 2 cents worth.

BTW, if you want to be able to test and tune your ignition curve, the E-MAG guys are neighbors and have a great product, as well.

$
 
I can tell you that most of the "issues" with the Surefly are the result of installation errors, or bad electical/ignition systems:

Capping the MP line when in fixed timing (MP sensor will through a fault code as the cap will overpressurize the sensor)

This was the only glitch in my installation of the SureFly. The docs with my unit said to cap the manifold pressure port if using fixed timing....which I did. The device wouldn't time properly and the nice guy at SureFly asked me if the pressure port was capped. Of course it was per the instructions.

I was informed the port cannot be capped because it confuses the software. I hope the documentation has been revised since then. My unit timed perfectly after the port was uncapped.
 
This was the only glitch in my installation of the SureFly. The docs with my unit said to cap the manifold pressure port if using fixed timing....which I did. The device wouldn't time properly and the nice guy at SureFly asked me if the pressure port was capped. Of course it was per the instructions.

I was informed the port cannot be capped because it confuses the software. I hope the documentation has been revised since then. My unit timed perfectly after the port was uncapped.

As you mentioned, if you cap the MP port with a rubber cover or a thread protector, you might presurized the MP sender to the point that it sends a rapid flashing light on the LED. This is an indication of a fault, in this case excessive MP. In the current installation manual, there is no mention of using a cap on the MP port. Probably worth putting in the troubleshooting guide.

$
 
No issues with install

I just replaced a Slick impulse-coupled mag with a SureFly unit. There was nothing in the STC documentation to direct capping the MP port, so I didn’t. The unit timed perfectly to the engine. Based on a number of forum opinions on advance timing, I elected to stick with fixed 25 deg BTDC timing. No issues whatsoever with install or operations.
 
I just replaced a Slick impulse-coupled mag with a SureFly unit. There was nothing in the STC documentation to direct capping the MP port, so I didn’t. The unit timed perfectly to the engine. Based on a number of forum opinions on advance timing, I elected to stick with fixed 25 deg BTDC timing. No issues whatsoever with install or operations.

I hope that once you have some inflight experience, you set the opinions aside and take advantage of the variable timing mode. The fact is that no one has had a catostrophic detonation event in variable timing with the Surefly.
 
What is the concern?

To be clear, we're talking about advance here, not product. There's much to like about the product.

Regarding advanced timing, for the average user the downside is higher temperatures for little return.

For the advanced user, no published advance schedules.

Is variable advance a bad thing? Of course not. It can be a useful tool.

You have a thread going right now:

https://vansairforce.net/community/showpost.php?p=1457430&postcount=17

Set your switches to fixed timing, and see what happens.
 
I am looking at installing a surefly as a mag replacement on one side of a IO540 parallel valve with a RSA 10 and 9.5 to 1 pistons. I have looked through all the pubs and read the threads. If I keep the left mag timed at 23 degrees BTDC how would most run the surefly? It appears that if I ran it with variable timing and set the baseline at 23 I would not see more than 34.5 degrees of advance with a RPM max of 2700. Am I understanding this correctly? It also seems with my preferred cruise RPM of 2200 the surefly advance curve would be close to what most suggest is optimal for LOP operations.
G
 
Last edited:
To be clear, we're talking about advance here, not product. There's much to like about the product.

Regarding advanced timing, for the average user the downside is higher temperatures for little return.

For the advanced user, no published advance schedules.

Is variable advance a bad thing? Of course not. It can be a useful tool.

You have a thread going right now:

https://vansairforce.net/community/showpost.php?p=1457430&postcount=17

Set your switches to fixed timing, and see what happens.

That's a fair opinion, and I appreciate your comments. What were your results when you tested this with the Surefly?

In my situation I've tested both:

Fixed timing: Same numbers as the magnetos but able to get farther LOP with a smooth running engine.

Variable timing: SIM is in fixed timing until below 25", so my only changes are at cruise. At cruise altitude (below 25" MP, WOT, 10,000', 8.0gph) at 100° ROP I've recorded a 10° increased CHT and 5° increase in oil temperature, and better speed (versus fixed timing cruise). Once LOP I can cool the engine much better than in fixed timing by smoothly going 50°-100° LOP, 6.2-6.5gph, while maintaining better speed than with fixed timing.

So, in my experience, the variable timing is well worth the performance gains.

You referenced a thread I have going about oil temperature cooling. This airplane has always had issues with cooling, long before I installed the Surefly and has no bearing on this discussion. Before taking out the big hammer and simply installing a bigger cooler, I fixed many issues which helped dramtically. All this was done before the Surefly's. I would still like to get the oil temperatures down, even though they are within limits. When I installed the Surefly's, I tested in both fixed and variable timing. The only temperature changes I observed was ROP cruise and cooler LOP cruise temperatures, as mentioned above. Good point to bring up, as one might have the opinion that I'm struggling with temperatures because of the Surefly, but I'm not.

$
 
Last edited:
I too installed a Surefly in place of the impulse mag on my RV 14-A. Quicker starts hot or cold and I spent 2 hours installing it after getting a manifold hose T-connection. I like the vacuum advance at cruise and currently collecting performance at different altitudes. Great customer support in Granbury if you have questions.
 
That's a fair opinion, and I appreciate your comments. What were your results when you tested this with the Surefly?

The system I've been flying since early 2016 is dual map. It also allows setting any advance schedule desired at 100 points.

With dual maps, I keep one set for 23 fixed (angle valve 390), and the other holds a schedule with advance based on MP and RPM. The current schedule is below. I can change back and forth in flight with the flick of a switch, which makes comparison easy.

For sure, the angle valve doesn't want as much advance as the parallel valve engines.

Fixed timing: Same numbers as the magnetos but able to get farther LOP with a smooth running engine.

Yep. And it starts better hot or cold, etc.

Variable timing: SIM is in fixed timing until below 25", so my only changes are at cruise.

In other words, choosing a fixed or advancing schedule would make no difference at all to a fellow who generally flies below, what, 6000 or so?

At cruise altitude (below 25" MP, WOT, 10,000', 8.0gph) at 100° ROP I've recorded a 10° increased CHT and 5° increase in oil temperature, and better speed (versus fixed timing cruise).

Average when ROP was 2.5 F CHT increase per degree of advance for a very similar engine.

So what is timing advancing to at that point, and how much faster do you go in return?

BTW, 8 gph is remarkable for 100 ROP at that altitude. Pulled to some very low RPM?
 

Attachments

  • Advance config.jpg
    Advance config.jpg
    45.4 KB · Views: 487
Last edited:
Apples to Oranges

If you are using a different ignition to form opinions about the Surefly in variable timing mode, it seems you are comparing apples to oranges, especially if your system is advancing differently than the Surefly. Is your advance the same as the Surefly's proprietary advance? Based on your question about the advance below 6000', it sounds like we are both unaware of the Surefly advance details.

Why is it proprietary? If it was public knowledge, Shanghai Ignitions could copy it and streamline the certification process with the FAA, using Surefly's realiability history in the field. (McDonald's Special Sauce).

If your opinions are based on experience with a different ignition system, then it's a shame that I read of users changing their base timing, avoiding varible timing, or not buying the SF based on these opinions.

It's up to all of us to make informed decisions. These forums are an excellent source of information. But, be sure to give the manufacturer a call, if you have questions.

$$
 
All that matters is total advance at any given MAP, RPM and AFR for MBT.

Ignitions which don't allow timing adjustment with regard for AFR cannot be fully optimized for LOP cruise since flame speeds varies considerably with AFR. I've published plenty of graphs here to illustrate this fact.

There are already too many ignition systems on the market with secret or proprietary ignition curves promising amazing things and we know of some that are worse than fixed timing mags.

A few hours of test flying with an ignition system having variable timing capability will get you 95% of the way there. No big secret sauce.

As with engines, airframes or most other things that fly, no ignition system is proven in my books until hundreds of examples have accumulated tens of thousands of hours in the real world and that feedback is in.

Other companies have been in this market for years or even decades and sold many thousands of EIs collectively. Surefly is the new kid on the block. Maybe they have it all right the first time around, maybe not. Only time will tell.
 
Last edited:
Jimmy, let's skip the straw man stuff and get back to the question at hand.

Regarding variable timing, you wrote..

.At cruise altitude (below 25" MP, WOT, 10,000', 8.0gph) at 100° ROP I've recorded a 10° increased CHT and 5° increase in oil temperature, and better speed (versus fixed timing cruise).

...but forgot to tell us how much better. So help the readers make an informed decision. What is the timing BTDC at that point, and how much faster do you go?
 
Regarding variable timing, you wrote..

.At cruise altitude (below 25" MP, WOT, 10,000', 8.0gph) at 100° ROP I've recorded a 10° increased CHT and 5° increase in oil temperature, and better speed (versus fixed timing cruise).

I'd be surprised if there is much to be gained with advanced timing running at 100 ROP and 25". Never seen that in any of my RV-10 flight testing on a PV engine.
 
I am looking at installing a surefly as a mag replacement on one side of a IO540 parallel valve with a RSA 10 and 9.5 to 1 pistons. I have looked through all the pubs and read the threads. If I keep the left mag timed at 23 degrees BTDC how would most run the surefly? It appears that if I ran it with variable timing and set the baseline at 23 I would not see more than 34.5 degrees of advance with a RPM max of 2700. Am I understanding this correctly? It also seems with my preferred cruise RPM of 2200 the surefly advance curve would be close to what most suggest is optimal for LOP operations.
G

Too many variables here to suggest that you are going to end up with an "optimal" advance with the canned SF curve. Maybe, maybe not. One thing for sure, the single fixed magneto is going to drag the total effective timing down to something less than the SF max advance is going to give you. Is that composite timing right for you? Only flight test -with the ability to change timing on the fly - will tell you for sure. Also beware of the 4 banger curves - few of them cruise at 2200 RPM like we do with the 6 bangers. The difference in piston speed is a significant factor in timing requirements.
 
Just to be clear, allow me to again state specifics.

(1) Regarding advanced timing, for the average user the downside is higher temperatures for little return. A high percentage of owners fight cooling issues. Adding to the problem is pointless.

(2) For the skilled user, no published advance schedules.

(3) Advance settings optimum for LOP are too advanced for ROP.

(4) Advance schedules optimized for parallel valve engines are generally too advanced for angle valve engines.

Again, this is NOT a brand criticism. These issues apply to other popular ignition system brands too.

Surefly installs faster than any system I've seen, and allows the user to select fixed timing. Those physical facts make it an easy EI replacement when Slick mags time out...again, in particular for the average fun flyer. "Easy replacement of Slick mags" was Surefly's #1 design goal, and they hit that nail square on the head.
 
Nope. They pulled it a while ago. It was a confusing chart but at least it was something.

OSH2019 Lycoming announced that they will be white labeling the SureFly ignition, changed colors :) and called it a Lycoming Electronic Ignition System (EIS).
Check out Lycoming Service Instruction No. 1443R.



Lenny, I have that one, formerly published on the company website. Is it still there and I've missed it?
 

Attachments

  • SI-1443R.png
    SI-1443R.png
    79.7 KB · Views: 337
Nope. They pulled it a while ago. It was a confusing chart but at least it was something.

OSH2019 Lycoming announced that they will be white labeling the SureFly ignition, changed colors :) and called it a Lycoming Electronic Ignition System (EIS). ....SNIP....

The Lycoming West Coast rep say's that is not accurate.
They say that the hardware is manufactured by Surefly but the the software/firmware is totally in-house.
 
I'm not buying that. :)

First, if I didn't want people messing with the settings I'd just disable the DIP switches in software and wouldn't just warn them not to mess with it or their engine will blow up.

Second, it wouldn't make a lot of financial sense for them to write their own code in-house and then certify it, when the hardware & software they are getting from SureFly is already certified. That involves thousands of hours of development and testing.


The Lycoming West Coast rep say's that is not accurate.
They say that the hardware is manufactured by Surefly but the the software/firmware is totally in-house.
 
At press time for OSH 2019, the Lycoming-branded versions were to have their own locked timing schedules, as determined in the Lycoming dyno facility. Those schedules were to be engine-specific, with a part number tied to each. At OSH 2019 the only approved version was fixed timing. Still is, best I know. Rumor says Surefly made some changes based on the Lycoming partnership...and the published schedule disappeared.

It's silly to claim a potential competitor might steal the secret advance maps if published. If a competitor cared what was in a Surefly, they could simply order one. The remaining espionage is low level stuff. Here's the required tool list:

variable speed lathe.
optical tach
degree wheel
timing light
vacuum pump, gauge
plug harness and misc hardware
12V power source

Set an RPM, confirm with the the tach. Set a MP with a bleed valve in the vacuum pump line. Vary it, read the timing from the degree wheel, record.

I guarantee will will not self destruct like something from the opening of a Mission Impossible film.
 
I'm not buying that. :)

First, if I didn't want people messing with the settings I'd just disable the DIP switches in software and wouldn't just warn them not to mess with it or their engine will blow up.

Second, it wouldn't make a lot of financial sense for them to write their own code in-house and then certify it, when the hardware & software they are getting from SureFly is already certified. That involves thousands of hours of development and testing.

It doesn't sound like there's any evidence that Lycoming's in house software/firmware development is not what they say it is.

I'l stick with Lycoming story until it's proven otherwise.
 
I am looking at installing a surefly as a mag replacement on one side of a IO540 parallel valve with a RSA 10 and 9.5 to 1 pistons. I have looked through all the pubs and read the threads. If I keep the left mag timed at 23 degrees BTDC how would most run the surefly? It appears that if I ran it with variable timing and set the baseline at 23 I would not see more than 34.5 degrees of advance with a RPM max of 2700. Am I understanding this correctly? It also seems with my preferred cruise RPM of 2200 the surefly advance curve would be close to what most suggest is optimal for LOP operations.
G

Install it according to the manual, and call Surefly if you have questions. You want the magneto and SIM to be at the same base timing. You time the SIM at 0° TDC, and the magneto at 23° BTDC. Your DIP switches should be set for 23° base timing on the SIM. The SIM will advance to as much as 38° in the variable timing mode. Again, call Surefly if you have questions.
 
Not sure why under any conditions, you'd want 38 degrees advance on a PV Lycoming and especially on an AV one.
 
Install it according to the manual, and call Surefly if you have questions. You want the magneto and SIM to be at the same base timing. You time the SIM at 0° TDC, and the magneto at 23° BTDC. Your DIP switches should be set for 23° base timing on the SIM. The SIM will advance to as much as 38° in the variable timing mode. Again, call Surefly if you have questions.

That’s how I would set it up. I don’t see it ever advancing to 38 degrees unless I am missing something. If the base timing is set to 23 the max advance should be 36 degrees at 3000 RPM. I run a max of 2700 rpm and at the altitude it starts advancing I am back at 2500. My normal cruise is 2200. It looks like the advance at my normal cruise altitude and power settings should be around 31. This seems pretty good for LOP operations. What am I missing?
 
Not sure why under any conditions, you'd want 38 degrees advance on a PV Lycoming and especially on an AV one.

Nigel's data (gathered with a high compression parallel valve, like PFB's) says speed continued to rise with increasing advance when operating LOP at higher altitudes, and the trend continued out past 38 degrees. So yes, given those conditions, an advanced user with an O2 bottle and a parallel valve can gain speed by adding lots of advance. How much? The reported difference between 25 degrees and 38 degrees was about 6 knots at 12K. The CHT increase was about 20F. To put it in practical terms, if I flew Nigel's RV-8 nonstop at 12K, OSH to my home base in south Alabama, using 38 degrees, I would trim 8 minutes off a four hour flight...about 2.2%

So, nothing wrong with advance for LOP cruise. That said, it is not a free lunch. Like most of our decisions, it involves balancing compromise, a benefit for a downside. Here the common downside is managing CHT while climbing up to that altitude, running ROP for power.

What am I missing?

A published RPM/MP advance schedule. Mighty hard to know what you have without one.
 
Last edited:
That’s how I would set it up. I don’t see it ever advancing to 38 degrees unless I am missing something. If the base timing is set to 23 the max advance should be 36 degrees at 3000 RPM. I run a max of 2700 rpm and at the altitude it starts advancing I am back at 2500. My normal cruise is 2200. It looks like the advance at my normal cruise altitude and power settings should be around 31. This seems pretty good for LOP operations. What am I missing?


If the single Surefly goes to 31 under the conditions you describe, the single fixed mag will drag the effective timing back to something like 27. Is 27 "optimal" for your setup? Only flight test will tell.
 
Nigel's data (gathered with a high compression parallel valve, like PFB's) says speed continued to rise with increasing advance when operating LOP at higher altitudes, and the trend continued out past 38 degrees. So yes, given those conditions, an advanced user with an O2 bottle and a parallel valve can gain speed by adding lots of advance. How much? The reported difference between 25 degrees and 38 degrees was about 6 knots at 12K. The CHT increase was about 20F. To put it in practical terms, if I flew Nigel's RV-8 nonstop at 12K, OSH to my home base in south Alabama, using 38 degrees, I would trim 8 minutes off a four hour flight...about 2.2%

So, nothing wrong with advance for LOP cruise. That said, it is not a free lunch. Like most of our decisions, it involves balancing compromise, a benefit for a downside. Here the common downside is managing CHT while climbing up to that altitude, running ROP for power.



A published RPM/MP advance schedule. Mighty hard to know what you have without one.

Interesting. In our flight testing, we found advance over 35 deg, around 50F LOP brought a reduction in speed right up to 20K which was as high as we went. Past this, CHTs increased for no speed increase.

Surefly doesn't know if you're ROP or LOP.

What does your testing show on your AV 390 Dan? Curious.
 
And a relevant datapoint - during my SDS testing on 91E10 fuel I found my limit at 31 degrees at 16/17k altitude when WOTLOP. 100LL would obviously tolerate a fair bit more timing. I have my limit set at 29 now.
 
What does your testing show on your AV 390 Dan? Curious.

I rarely pull mixture much past peak in cross country cruise, as I am not willing to accept the speed loss.

Here's an example, playing around with advance while returning from OSH 2019. I'm at peak EGT or a little leaner, right where speed starts to slip. Left photo is about 28 degrees; note MP/RPM and see the schedule a few posts back. Right photo is 23 degrees, re-stabilized about 30 minutes later.

You've seen the combustion speed charts. If I pull leaner, both speeds drop off, but the 28 degree speed will probably match the 23 degree speed, and fuel burn will drop a little. Pull a lot leaner, go a lot slower, burn even less fuel, and the advanced timing would probably be superior. That's the obvious route to flight duration, but this setup is already giving an honest four hours with reserve.
.
 

Attachments

  • 28 vs 23.jpg
    28 vs 23.jpg
    102.9 KB · Views: 322
It appears from this Lycoming document that all approved timing with their EI is fixed- no additional MAP advance. Is that how you read this too Dan?

Currently only one model has an approved variable timing part number, the IO-390D, in four configurations. Don't know if any customers are using the variable option in the field. Maybe CubCrafters with their "CC393i", which is a D3B6. I was researching 390 variants for an upcoming article, but we ran out of space, so I stopped.

The application document is SI 1443R. It is titled as a app doc for Slick mags, but includes all the EIS approvals.
.
 

Attachments

  • ScreenHunter_708 Sep. 03 06.32.jpg
    ScreenHunter_708 Sep. 03 06.32.jpg
    142.1 KB · Views: 291
Looks like they are performing testing to determine safe mapping- good idea. Get the product out on the market with fixed timing now and users can hopefully update to variable timing when the data is in.
 
Surefly ignition

We running Lycoming IO-390 with dual Surefly. We have used variable and fixed timing setting and found petter performance with fixed timing mode. If you read the EAA Cafe Foundation articles of magneto vs electronic ignition operations on a Mooney, only savings I’d found is with LOP above 12k, best climb and best power cruise is with fixed timing. With this engine on my RV8 we easily get 190kts at 8k and find cooler cylinder and oil temps with fixed timing.
 
That CAFE article was cutting edge for its day, but that day has long since passed. The EI's available today are far more capable and the experience base is much greater. There is still some validity to the flight test series back then, but the blanket statement that EI is "only good for x..." is very short sighted. Variable timing, properly executed, is a very good thing for an aircraft engine.
 
The EI's available today are far more capable and the experience base is much greater.

More capable how Mike? Some have dual maps, some offer adjustability, and I'm sure electronic components more reliable...but the question is to advance or not, and how much. I'm hard pressed to see how anything has changed.
 
Best thing I did with my SureFly on my Husky was set it to fixed timing. It has a angle-valve engine and those have been said to be more finicky with respect to variable timing. Plus the mission profile of a bush plane negates any value to the altitude cruise benefits of advance timing curves.

I want solid reliability with good temperatures. Any economy savings is farther down my list.

In fact I wish PMags had a fixed timing option. I also can't believe PMags don't come with a jumper already installed for the more mild advance curve out of the box. So I see the SureFly legacy-emulating fixed timing option as a plus.

Jim
 
MAP and Pressure Altitude

This question is directed at Ross, but can be commented by other knowledgable folks:

Why not adjust timing with both MAP and pressure altitude?

Here's why: A partial throttle climb will force most electronic ignitions to advance timing. The slower speeds at climb and the advanced timing can cause high CHTs.

Instead, use both PA and MAP to provide timing advance. Use a more conservative timing advance when the PA compared to MAP indicates partial throttle operation.

I can actually test this with my homebrew timing controller, but Ross has forgotten more than I know and I hoping for some insight.

V
 
More capable how Mike? Some have dual maps, some offer adjustability, and I'm sure electronic components more reliable...but the question is to advance or not, and how much. I'm hard pressed to see how anything has changed.

The EI used in the CAFE article was an early Electroair unit - hardly the latest word in adjustability, and most significantly, the Mooney used in the test series had an Angle Valve under the cowl - which is now known to be a whole different animal compared to the much more common PV most of us fly. As a result, the test series was significantly non representative for todays products and most common equipment.

It is known that PV Lycomings like huge advance at idle, suffer almost no loss in power (but much cooler CHT and increased detonation margin) with significant retard at TO power settings, do great with data plate settings when ROP, and like a bunch of advance when LOP. That data set was not fully explored in the CAFE test series.

The question is more complex than "how much to advance" - it's "what does the engine need?". That may be a significant retard as well as a significant advance. Unlike 1995, you can buy an ignition that does both today - That's what has changed.
 
Last edited:
This question is directed at Ross, but can be commented by other knowledgable folks:

Why not adjust timing with both MAP and pressure altitude?

Here's why: A partial throttle climb will force most electronic ignitions to advance timing. The slower speeds at climb and the advanced timing can cause high CHTs.

Instead, use both PA and MAP to provide timing advance. Use a more conservative timing advance when the PA compared to MAP indicates partial throttle operation.

I can actually test this with my homebrew timing controller, but Ross has forgotten more than I know and I hoping for some insight.

V

The big reason is the engine cares very little about pressure altitude regarding ignition timing. MAP is the most significant parameter in the operational RPM range (2300-2700) followed by AFR.

The engine doesn't care whether MAP is being restricted with less than full throttle or if the drop is due to altitude increase at WOT.

Heat is less at partial throttle as HP is less so CHT should be less as well. The problem is many EIs overly advance timing at lower MAP, it seems because they never did proper testing to determine what's optimal and their architecture makes changing the timing curve a chore or impossible in some cases.
 
The big reason is the engine cares very little about pressure altitude regarding ignition timing. MAP is the most significant parameter in the operational RPM range (2300-2700) followed by AFR.

The engine doesn't care whether MAP is being restricted with less than full throttle or if the drop is due to altitude increase at WOT.

Heat is less at partial throttle as HP is less so CHT should be less as well. The problem is many EIs overly advance timing at lower MAP, it seems because they never did proper testing to determine what's optimal and their architecture makes changing the timing curve a chore or impossible in some cases.

The point I was trying to make, is that a partial power climb can benefit from a more conservative advance. I know that SDS has an LOP switch for cruise, which means that you have a more conservative advance curve until the pilot determines cruise configuration and switches to cruise mode. I was thinking that this can be automated, but I like the idea of pilot control.

Perhaps this idea is more about the limitations of competing systems than the SDS system.

V
 
Back
Top