[rph142]

I’ve been chasing high cht’s since first flying my new Titan IO-370 w/9.6:1, cold air sump, dual p mags w/jumpers installed and afp fm150. It has a plenum which I designed under a Sam James cowl. I filed the flashing between fins, sealed every conceivable exit path with rtv, installed a lower cowl bump, installed two cowl flaps, and cleaned up the exit path all to no avail. On a recent trip I had cht’s hovering at 400-405f at 10500 msl and 80f oat and cruise power (I should note it was the hottest day on record on earth a couple hundred miles to the south in death valley). Regardless of the oat, this engine consistently ran hotter than the high compression IO-320 I had in my -3. Running LOP didn’t seem to make much of a difference.

This afternoon I decided to check the timing of both pmags. It turns out the factory installed them right at tc. Pmags must be shifted 1-6 degrees after tc in order to time the motor to the required 20 degrees btdc. I “reclocked” the mags @ +5 and test flew in 100f OAT. My cht’s are now peaking at 380f! No cowl flaps required!! I’m posting this as a cautionary tale for anyone chasing high cht’s. The engine also starts much easier and static WOT rpm is at least 20rpm higher.

 

[Walt]

I have the same engine but I opted for Bendix mags, I refuse to run that much advance with high compression.
My CHT’s are typically <350, I’ve never seen >400 even in a hard climb in Tx.
Stock cowl.

 

[Av8torTom]

20 degrees btdc is what's recommended for my Superior Air parts XO-320, 160 HP engine.
I'm having similar CHT issues with my Sam James Cowl with custom plenum. I spoke to the pmag folks and they recommended trying to retard the timing 2 degrees.

 

[Carlos151]

20 degrees btdc is what's recommended for my Superior Air parts XO-320, 160 HP engine.
I'm having similar CHT issues with my Sam James Cowl with custom plenum. I spoke to the pmag folks and they recommended trying to retard the timing 2 degrees.

Not with P-Mags. Top center or 1-6 degrees after TC according to their install manual.

 

[georgemohr]

You guys are really saying the same thing. All engines require a set timing Before Top-dead Center (BTC) prescribed by the engine manufacturer. The difference is the way you set this timing on a traditional mag vs a P-mag.

Traditional mags are timed with the index mark at 20 or 25 deg BTC. Pmags need the same timing, but use the TC index mark and are set at TC (for 25 BTC) or TC+5 degrees (for 20 BTC). It just a difference of reference point. One can fine tune the timing by varying this offset from TC by a degree or two or three to get a desired result (if one is knowledgeable and careful, timing is no joke and advanced timings are potentially dangerous).

 

[Walt]

Even with the jumper in you have 34deg advance, if you clock it back 4 deg you still have 30 on engine that specs 20 deg.
The only way to defeat that is with a custom program loaded to the PMAG which they recommend against.

b. Jumper IN: Installing a jumper between #2 and #3 enable the “A” curve, which allows timing to advance, typically, as much as 34 degrees - a less aggressive advance range.

Note PMAG's warning in the manual:
Different fuels, compression ratios, and other conditions may require further adjustment. IN ALL CASES, operators are responsible for determining proper settings

 

[Carl Froehlich]

Even with the jumper in you have 34deg advance, if you clock it back 4 deg you still have 30 on engine that specs 20 deg.
The only way to defeat that is with a custom program loaded to the PMAG which they recommend against.

Walt - this is misleading.

For example, with jumper in pMag will advance a maximum of 9 degrees. But, this advance is dependent on RPM and MP. So full power (WOT) takeoff timing is about at base timing (e.g. 25 degrees for parallel valve, 20 for angle head) same as a mag. At altitude and WOT timing will start to advance (as is desired) for cruise efficency). Even here advance tends to be less than 9 degrees.

Timing advance is needed to keep cylinder peak pressure at about the same point as altitude increases. All the data I’ve seen indicates 9 degrees as thumb rule target.

Carl

 

[Mconner7]

I’ve been chasing high cht’s since first flying my new Titan IO-370 w/9.6:1, cold air sump, dual p mags w/jumpers installed and afp fm150. It has a plenum which I designed under a Sam James cowl. I filed the flashing between fins, sealed every conceivable exit path with rtv, installed a lower cowl bump, installed two cowl flaps, and cleaned up the exit path all to no avail. On a recent trip I had cht’s hovering at 400-405f at 10500 msl and 80f oat and cruise power (I should note it was the hottest day on record on earth a couple hundred miles to the south in death valley). Regardless of the oat, this engine consistently ran hotter than the high compression IO-320 I had in my -3. Running LOP didn’t seem to make much of a difference.

This afternoon I decided to check the timing of both pmags. It turns out the factory installed them right at tc. Pmags must be shifted 1-6 degrees after tc in order to time the motor to the required 20 degrees btdc. I “reclocked” the mags @ +5 and test flew in 100f OAT. My cht’s are now peaking at 380f! No cowl claps required!! I’m posting this as a cautionary tale for anyone chasing high cht’s. The engine also starts much easier and static WOT rpm is at least 20rpm higher.

I had similar issues on my O-540 after I rebuilt it. It has one Slick and one SureFly SIM. A mag check showed the SIM was the issue. I consulted with SureFly and tried retarding the timing 2* with some decrease in CHT. I then selected fixed timing and problem was solved.

 

[Traash]

IO-540 D4A5 w/ 9.1 Pistons likes 23*.
Data plate assumes 8.7 Pistons and calls for 25*.

 

[Walt]

Walt - this is misleading.

For example, with jumper in pMag will advance a maximum of 9 degrees. But, this advance is dependent on RPM and MP. So full power (WOT) takeoff timing is about at base timing (e.g. 25 degrees for parallel valve, 20 for angle head) same as a mag. At altitude and WOT timing will start to advance (as is desired) for cruise efficency). Even here advance tends to be less than 9 degrees.

Timing advance is needed to keep cylinder peak pressure at about the same point as altitude increases. All the data I’ve seen indicates 9 degrees as thumb rule target.

Carl

Can you show me the advance curve for RPM/MP?
What happens when I take off in Colorado?

 

[rph142]

Here’s the pmag timing curve off of their website (for representation purposes only and not the actual curve). MAP rolls into it as well somehow. I wish they would post the actual curve with rpm and map variables.

 

[DanH]

Walt - this is misleading.

Timing advance is needed to keep cylinder peak pressure at about the same point as altitude increases. All the data I’ve seen indicates 9 degrees as thumb rule target.

Kinda unfair to call Walt "misleading" and post the above.

I'd like to see your data regarding required advance to keep peak pressure at the same point with altitude increase. Academic interest, because even if true it doesn't appear to have much practical value, at least with a 6-7-8. Results may be a little better for later wings.

 

[Brantel]

Here is a real world map of the P-Mag with the jumper out and factory settings. To convert to what you will get with the jumper in, subtract 5.647 from these numbers.

These values were captured in flight using three different monitoring devices (EI Commander, EI CAD, and Home Brew Monitor) and they all agreed with each other.

Walt is basically correct when he said you can still see up to 34 degrees of advance with the jumper in. (There is rounding involved. The P-Mag uses an 8 bit processor and non floating point math (360/255= ~1.41176 degree resolution)

Once I learned what I know about the P-mags, I programmed mine for no advance at all above the engine data plate and essentially forgot about them and my engine was much happier with reduced CHT's. Mine was a standard compression engine. No way I would run this kind of advance with a high compression engine.

 

[NTex]

Here is a real world map of the P-Mag with the jumper out and factory settings. To convert to what you will get with the jumper in, subtract 5.725 from these numbers.

These values were captured in flight using three different monitoring devices (EI Commander, EI CAD, and Home Brew Monitor) and they all agreed with each other.

Walt is basically correct when he said you can still see up to 34 degrees of advance with the jumper in. (There is rounding involved. The P-Mag uses an 8 bit processor and non floating point math (360/255= ~1.41176 degree resolution)

Once I learned what I know about the P-mags, I programmed mine for no advance at all above the engine data plate and essentially forgot about them and my engine was much happier with reduced CHT's.

View attachment 66300

Wow thanks Brian.

Seems odd pmag won't publish the actual timing curve, even more surprising is that with the jumper in, at all MP/RPM combinations you're still running an advance.

Agree with your approach to modify the PMag factory timing settings to go back to OEM lycoming timing.

 

[wirejock]

Here is a real world map of the P-Mag with the jumper out and factory settings. To convert to what you will get with the jumper in, subtract 5.647 from these numbers.

These values were captured in flight using three different monitoring devices (EI Commander, EI CAD, and Home Brew Monitor) and they all agreed with each other.

Walt is basically correct when he said you can still see up to 34 degrees of advance with the jumper in. (There is rounding involved. The P-Mag uses an 8 bit processor and non floating point math (360/255= ~1.41176 degree resolution)

Once I learned what I know about the P-mags, I programmed mine for no advance at all above the engine data plate and essentially forgot about them and my engine was much happier with reduced CHT's. Mine was a standard compression engine. No way I would run this kind of advance with a high compression engine.

View attachment 66300

Brian
I would like to program my "B" curve to match the "A" or even less advance. Would you share settings? Maybe some screen shots?

 

[Walt]

So now we come full circle, what exactly are you getting when you "upgrade" to PMAGS from standard mags?
(a bit of a rhetorical question)

 

[Taltruda]

Here is a real world map of the P-Mag with the jumper out and factory settings. To convert to what you will get with the jumper in, subtract 5.647 from these numbers.

These values were captured in flight using three different monitoring devices (EI Commander, EI CAD, and Home Brew Monitor) and they all agreed with each other.

Walt is basically correct when he said you can still see up to 34 degrees of advance with the jumper in. (There is rounding involved. The P-Mag uses an 8 bit processor and non floating point math (360/255= ~1.41176 degree resolution)

Once I learned what I know about the P-mags, I programmed mine for no advance at all above the engine data plate and essentially forgot about them and my engine was much happier with reduced CHT's. Mine was a standard compression engine. No way I would run this kind of advance with a high compression engine.

View attachment 66300

If you are using no advance above the data plate, then you are operating retarded most of the time? What’s the advantage over standard mags then? The whole point of electronic ignition is to utilize the advance at reduced manifold pressure (either from a power reduction or higher altitude)

 

[Brantel]

If you are using no advance above the data plate, then you are operating retarded most of the time? What’s the advantage over standard mags then? The whole point of electronic ignition is to utilize the advance at reduced manifold pressure (either from a power reduction or higher altitude)

That is exactly what I was doing but I was not operating retarded, I was operating at the OEM's recommended advance angle for my engine which in my case was 25° BTDC. There are many other advantages other than additional advance to using an electronic ignition over standard mags. For most of us, these high advance numbers offer little benefit. Take a look at Dan's post #12 above.

 

[Brantel]

So now we come full circle, what exactly are you getting when you "upgrade" to PMAGS from standard mags?
(a bit of a rhetorical question)

For me it was super easy starting in all conditions and the ability to run car plugs. They appeared to me a bit smoother than normal mags but that can be subjective. They did allow me to get deeper into the LOP region but since I had a carb with horrible EGT separation, I could not fully take advantage of this.

One could make both plus and minus comments about them being lower maintenance but there again that would be subjective.

 

[Brantel]

Brian
I would like to program my "B" curve to match the "A" or even less advance. Would you share settings? Maybe some screen shots?

Since I no longer have access to the airplane and a poor memory, I can't give you the exact settings and I don't have screenshots. I can tell you I did it all with the EI CAD software but it can also be done with the EI Commander and the Engine Bridge.

The easiest thing is to just set the max advance limit to whatever you want the max advance to be and that will become the ceiling. Optional to play around with the advance shift variable. It just moves the whole curve up and down.

 

[Toobuilder]

For most of us, these high advance numbers offer little benefit. Take a look at Dan's post #12 above.

Are we looking at the same graph? Because the one I see shows a significant TAS penalty by running the locked out data plate timing value vs. “optimum“ advance at any reasonable altitude. Some of us would give up a body part before giving up 5 knots at cruise.

But the basic premise of the thread is spot on. “Too much” timing is not a good thing. It’s what many of us have been preaching for many years. It also illustrates the dangers of using a “one size fits all“ ignition curve, when we should all be at least be aware that there is no such thing. It’s somewhat amusing that people continue to choose a product that is a poor fit for their application, then blame the capability of that product as the root cause. Let’s be clear - variable advance has significant performance benefits in an aircraft engine. Period. Dot. That said, people should not badmouth the capability of variable advance just because they chose the wrong product or don’t understand how to use the capability properly.

 

[Toobuilder]

Here is a real world map of the P-Mag with the jumper out and factory settings.

Not going to get into a manufacturer bash here, but if those are true numbers that is frightening. For example, your graph for 2700 RPM and 28 inches is my typical takeoff power numbers for my home airport. If I’m reading your graph right, the Pmag is throwing 32.2 degrees at the engine. In contrast, my ignition is programmed to provide 18 degrees at the same power setting. And as a review, my engine is a PV with stock (8.5) pistons. There is no way I would run 32 degrees under those conditions.

 

[Brantel]

Not going to get into a manufacturer bash here, but if those are true numbers that is frightening. For example, your graph for 2700 RPM and 28 inches is my typical takeoff power numbers for my home airport. If I’m reading your graph right, the Pmag is throwing 32.2 degrees at the engine. In contrast, my ignition is programmed to provide 18 degrees at the same power setting. And as a review, my engine is a PV with stock (8.5) pistons. There is no way I would run 32 degrees under those conditions.

Its very real and why I decided to take the actions that I did.

 

[Toobuilder]

Its very real and why I decided to take the actions that I did.

I remember seeing that graph back in the day but didn’t realize the magnitude of the curve. I appreciate you collecting data. We’re all a bit smarter as a result.

 

[noahhl]

Not going to get into a manufacturer bash here, but if those are true numbers that is frightening. For example, your graph for 2700 RPM and 28 inches is my typical takeoff power numbers for my home airport. If I’m reading your graph right, the Pmag is throwing 32.2 degrees at the engine. In contrast, my ignition is programmed to provide 18 degrees at the same power setting. And as a review, my engine is a PV with stock (8.5) pistons. There is no way I would run 32 degrees under those conditions.

It's an accurate timing map based on my data, but the fact that it's for the more aggressive jumper-out curve makes it seem more alarming -- these aren't the recommended settings per the manual. For an engine that has 25 BTDC on the nameplate, following the suggested settings (jumper in, timed at TDC) will result in timing at 26.4 degrees BTDC at 28" MAP. For an engine with 20 BTDC on the nameplate, it would be 21.4 degrees. I'm fairly sure this is how it comes pre-set on a new engine from Lycoming (but I've pulled the jumper to use an EngineBridge and retimed, so can't confirm).

I run my p-mags with a -1.4 degree shift, which I think is fairly common, to bring it back to 25 BTDC at 28" MAP. With those settings, timing advance vs MP and RPM over a flight that involved some cruise, an approach, and a couple of full stop landings looks like:

 

[Toobuilder]

It's an accurate timing map based on my data, but the fact that it's for the more aggressive jumper-out curve makes it seem more alarming -- these aren't the recommended settings per the manual.

Copy that, but why even offer this more aggressive curve at all? I can’t think of a Lycoming configuration that would benefit from such an aggressive initial advance. That, and how many customers are flying around with the jumper out, timed at “0”, blissfully ignorant? How many of THOSE are flying an angle valve? (I’ll sheepishly admit that I was an early adopter of Pmags and flew an angle valve with the jumper out).

 

[DanH]

Copy that, but why even offer this more aggressive curve at all? I can’t think of a Lycoming configuration that would benefit from such an aggressive initial advance. That, and how many customers are flying around with the jumper out, timed at “0”, blissfully ignorant? How many of THOSE are flying an angle valve? (I’ll sheepishly admit that I was an early adopter of Pmags and flew an angle valve with the jumper out).

That's a very good question. Speculation, but perhaps a base function of the selected ignition chip? I note the later design 6-cyl version has a fixed timing option.

I've done some limited 390 testing up high with significant advance. All it does is make it slower and hotter. If you're an RV-14 owner with p-mags, install the jumper and clock the installation at least 6 degrees.

So now we come full circle, what exactly are you getting when you "upgrade" to PMAGS from standard mags?
(a bit of a rhetorical question)

Not really. I'll make a gut estimate...more than 50% of p-mag users bought them for the self-generating feature. If advance functions played in the decision, for most of them it was a response to marketing...no deep understanding or specific desire.

 

[Walt]

Not really. I'll make a gut estimate...more than 50% of p-mag users bought them for the self-generating feature. If advance functions played in the decision, for most of them it was a response to marketing...no deep understanding or specific desire.

Pretty sure Mags are self-generating!

 

[wirejock]

It's an accurate timing map based on my data, but the fact that it's for the more aggressive jumper-out curve makes it seem more alarming -- these aren't the recommended settings per the manual. For an engine that has 25 BTDC on the nameplate, following the suggested settings (jumper in, timed at TDC) will result in timing at 26.4 degrees BTDC at 28" MAP. For an engine with 20 BTDC on the nameplate, it would be 21.4 degrees. I'm fairly sure this is how it comes pre-set on a new engine from Lycoming (but I've pulled the jumper to use an EngineBridge and retimed, so can't confirm).

I run my p-mags with a -1.4 degree shift, which I think is fairly common, to bring it back to 25 BTDC at 28" MAP. With those settings, timing advance vs MP and RPM over a flight that involved some cruise, an approach, and a couple of full stop landings looks like: View attachment 66305

For the benefit of a blissfully ignorant old man, how do you get a -1.4 shift?
Is that one of the "B" curve settings or did you time the P-mags some amount After TDC? How much?

 

[noahhl]

For the benefit of a blissfully ignorant old man, how do you get a -1.4 shift?
Is that one of the "B" curve settings or did you time the P-mags some amount After TDC? How much?

I have an Engine Bridge hooked up, which lets me change advance shift and max advance (but not the shape of the curve in between). EICAD or EICommander would be able to do the same.

 

[DanH]

Pretty sure Mags are self-generating!

Good point. I ran off the rails. What I was trying to say was self generation makes them equivalent to mags in the minds of many owners...which does not address your question.

 

[rmarshall234]

This conversation has turned to the question I’ve been asking online for over a decade now….with the exception of one or two, how come the manufacturers of electronic ignition systems don’t show us what the timing is with a cockpit display? This is the Information Age after all. Knowing in realtime what the timing is seems just as important to me as CHT and EGT and is the third piece of information I want when analyzing those first two.

 

[Carl Froehlich]

To the question of why use pMags at all.

As my other projects start life with dual pMags I do not have comparison data on pMag advantages. But, I do have one “before and after” for pMag gains. Four years ago I replaced the right mag on my old RV-10 with a pMag. The owner flew the plane up to my place for the update.

Here is a data point from the plane a couple of days before install on the trip to VA42 from Florida. For this trip the plane was flown solo, with perhaps 150 pounds of cargo. Same loading as after install:

- 9K’, 2380 RPM, LOP 20 degrees, 164kts TAS, 11.3-11.7 GPH

Here is data from the same plane, same loading, same pilot flown the same way on the return trip right after the upgrade:
- 12K’, LOP, 169kts TAS, 2380 RPM, 19.8” MP, 9.6 GPH. CHTs in the 350-360 range.
- 10K’ LOP, 169kts TAS, 10.1 GPH
- 12K’ ROP, 177kts TAS, 12.7 GPH

For the six cylinder pMag you set the timing advance to whatever you want. I set the MIN timing at 25 degrees BTDC (same as the mag), MAX timing at 34 degrees BTDC (same as the standard four cylinder pMag).

The primary gain with this pMag is cruise efficiency. Other pMag advantages include easy starts, auto plugs and no ignition backup batteries. If you blast around at full throttle, full rich all the time then mags will work just as well.

Some other thoughts:
- Most of my pMag experience is on parallel valve Lycomings (IO-360 and IO-540). I did do a dual install on an RV-14 IO-390 with timing set at 5-6 degrees ATDC. No problems.
- On the parallel four cylinder engines I run 25 degrees base timing (timing set at TDC) with jumper in. CHTs are well below 360 in cruise. On a hot day climb out I might get a little above 400 degrees, but alway below 420. I do from time to time run at PEAK in cruise to get CHTs above 320 or so (as discussed by Mike Bush to reduce exhaust valve sticking when using 100LL).

Happy to provide screen shots of my current ride (RV-8) for anyone interested. I’m at 500 hours on this plane and happy to report it is nicely dialed in.

Carl

 

[Toobuilder]

This conversation has turned to the question I’ve been asking online for over a decade now….with the exception of one or two, how come the manufacturers of electronic ignition systems don’t show us what the timing is with a cockpit display? This is the Information Age after all. Knowing in realtime what the timing is seems just as important to me as CHT and EGT and is the third piece of information I want when analyzing those first two.

In my opinion, based on watching this EI saga unfold for 20+ years, is there has been a slow culture shift that is driven by exposure and education. I think it was simply too much to throw a “radical” new technology like EI at the incredibly conservative pilot community and also expect them to monitor and understand the values being displayed. as long as it worked, and the experience matched the marketing “starts like a car!”, then that was good enough. Even today, some pilots will point to the mere ability to tune their ignition as a downside. These are many of the same pilots who spent the last several years building their entire airplane, but will balk at one more “learning opportunity”. Also look at one of the early EFI providers…. His marketing was a “plug and play” experience with the programming locked down, despite their use of CPU hardware that was fully tunable by the user. This same vendor changed his strategy 180 degrees once he saw that the market favored tuning by the end user.

Bottom line- I don’t think most users were ready for this much information back when some of the older units were developed. But today, I agree that knowing what the ignition is doing in real time is a valuable bit of information. And it wasn’t until I found a product that offered this feature that I realized just how valuable it is.

 

[erich weaver]

For the benefit of a blissfully ignorant old man, how do you get a -1.4 shift?
Is that one of the "B" curve settings or did you time the P-mags some amount After TDC? How much?

Instead of timing my pmags at TDC, I moved the prop forward a bit. I have a 149 tooth ring gear, so 360 degrees divided by 149 equals 2.4 degrees per tooth. For me, shifting the prop forward two teeth took care of occasional kick back problems during start up and also decreased my CHTs significantly. I didn’t notice any associated speed drop.

 

[rmarshall234]

In my opinion, based on watching this EI saga unfold for 20+ years, is there has been a slow culture shift that is driven by exposure and education. I think it was simply too much to throw a “radical” new technology like EI at the incredibly conservative pilot community and also expect them to monitor and understand the values being displayed. as long as it worked, and the experience matched the marketing “starts like a car!”, then that was good enough. Even today, some pilots will point to the mere ability to tune their ignition as a downside. These are many of the same pilots who spent the last several years building their entire airplane, but will balk at one more “learning opportunity”. Also look at one of the early EFI providers…. His marketing was a “plug and play” experience with the programming locked down, despite their use of CPU hardware that was fully tunable by the user. This same vendor changed his strategy 180 degrees once he saw that the market favored tuning by the end user.

Bottom line- I don’t think most users were ready for this much information back when some of the older units were developed. But today, I agree that knowing what the ignition is doing in real time is a valuable bit of information. And it wasn’t until I found a product that offered this feature that I realized just how valuable it is.

Thank You!

Finally an answer, and one that makes perfect sense.

I had a cockpit display with my original Ted Rose Electro Air unit on my RV-3 and that was more than 20 years ago. He treated us like adults. Recently picked up one of those NOS units and will be installing on my biplane soon.

”Blissful Ignorance”. Yep, a great marketing strategy

 

[aturner]

It so happens that I recently installed a pair of Series 200-6X E-MAG ignitions on my RV-10, and I'm fond of collecting and analyzing performance data. My system has the fixed-variable switch, so testing the effects of advanced timing is as simple as flipping a switch. I'm nowhere done crunching numbers, but here are a couple of preliminary results. My base is set at 23 deg. in order to help CHT's with those summertime quick turn fuel stops followed by a long climb to altitude - the original topic of this thread (and it does help). All data points represent five minutes of steady state cruise; data averaged from the one observation per second data logged by the G3X. No cherry picking here. I think the best way to do these tests is to perform a mixture sweep, and then show the effects of fixed vs. variable across a range of fuel flows where all other factors are held constant. Here is an early test with airspeed against fuel flow overlaid on isopleths for specific range. Overall, a 3% improvement in specific range with variable timing, or about 0.5 nmpg.


Peak EGT for the above test would be about 10.5 gph. It is clear that variable timing doesn't help when rich of peak, and has only a modest effect when LOP. Here is an example from a lower altitude and a bit more advance:

Here we have a 3.2% improvement in specific range (again, average = 0.5 nmpg) when using variable timing. These results square with those Nigel Speedy reports here: https://www.kitplanes.com/the-effec...linder-head-temperature-speed-and-efficiency/

As Nigel points out, you can improve efficiency more simply by climbing a little higher. In my case, the coefficient on the graph of specific range against altitude is 0.32, meaning I gain 0.32 nmpg per 1000 ft altitude, so climbing 2000 feet higher on a cross country, to the next cardinal altitude, helps economy more than flipping the variable timing switch.


Stay tuned.....in the process of crunching numbers for a higher altitude flight, and pulling out old data to test the theory that these new electronic ignition systems are yielding better economy than the old Slick mags.

 

[DanH]

Nice work Andy.

It would be fun to fly the identical procedure, same as Fig 2 but for the angle valve 390. Looks like the plan is to lock altitude, MP, RPM, then collect ten fuel flow data points, five each for base and advanced timing. Given the points are not quite aligned on the Y axis, I'm guessing you ran five points at base, then repeated five with advance? Or did you set a fuel flow and run five minutes at base, then switch timing, run five with advance, then switch to the next fuel flow?

 

[aturner]

Given the points are not quite aligned on the Y axis, I'm guessing you ran five points at base, then repeated five with advance? Or did you set a fuel flow and run five minutes at base, then switch timing, run five with advance, then switch to the next fuel flow?

The latter - I set fuel flow and ran five min at variable and then five at base, then readjusted fuel flow, allowing two minutes between data blocks to get the fuel flow set about where I wanted it. You want to do it this way to minimize the effects of any confounding effects that may be slowly changing over he course of the flight. I’m also puzzled by the small shift in fuel flow between base and advanced. ??

 

[DanH]

The latter - I set fuel flow and ran five min at variable and then five at base, then readjusted fuel flow, allowing two minutes between data blocks to get the fuel flow set about where I wanted it. You want to do it this way to minimize the effects of any confounding effects that may be slowly changing over he course of the flight. I’m also puzzled by the small shift in fuel flow between base and advanced. ??

Got it. I can do the same with the EDIS-based ignition.

The shift is indeed interesting. Two questions; What sort of fuel system are you flying here, and what is the EGT shift when you flip the timing switch?

Thinking out loud, I'd say timing doesn't change any of the mechanical relationships. However, advance does reduce cylinder pressure at EVO, so I would expect a change at overlap. Recall the whole point of overlap in cam timing is to use the exhaust negative wave to help get the intake flow moving. A reduction in negative pressure at overlap would indeed drop fuel flow slightly.

 

[walkman]

Got it. I can do the same with the EDIS-based ignition.

The shift is indeed interesting. Two questions; What sort of fuel system are you flying here, and what is the EGT shift when you flip the timing switch?

Thinking out loud, I'd say timing doesn't change any of the mechanical relationships. However, advance does reduce cylinder pressure at EVO, so I would expect a change at overlap. Recall the whole point of overlap in cam timing is to use the exhaust negative wave to help get the intake flow moving. A reduction in negative pressure at overlap would indeed drop fuel flow slightly.

What's the benefit of introducing EDIS into the system? Is it the "limp home" mode? Does that even work on our engines?

 

[aturner]

The shift is indeed interesting. Two questions; What sort of fuel system are you flying here, and what is the EGT shift when you flip the timing switch?

Vanilla Bendix RSA-5 with reasonably balanced injectors. For Fig. 1, EGT rise with the flip to fixed ranges from 35-80 deg. F, with the larger rise of course at leaner mixtures.

 

[DanH]

What's the benefit of introducing EDIS into the system? Is it the "limp home" mode? Does that even work on our engines?

Same benefits as any other EI

An EDIS module reverts to 10 BTDC if disconnected from its control computer. I'm confident a Lycoming will run at 10 degrees, but I've never tried it, given I'm running two separate controllers.

 

[DanH]

Vanilla Bendix RSA-5 with reasonably balanced injectors. For Fig. 1, EGT rise with the flip to fixed ranges from 35-80 deg. F, with the larger rise of course at leaner mixtures.

A gas temperature drop would slow exhaust waves, delaying the desired negative wave arrival during overlap. It's a classic "on the cam" effect.

I previously ran some tests to determine deltaP across the injector bleeds using a fast pressure sensor tapped to a primer port. Used a second channel to record ignition firing on #1, which gave me a reference marker for when each intake wave was arriving at the port. The same setup would show a change if the above theory is correct. Hmmm....

 

[walkman]

Same benefits as any other EI

An EDIS module reverts to 10 BTDC if disconnected from its control computer. I'm confident a Lycoming will run at 10 degrees, but I've never tried it, given I'm running two separate controllers.

Yep, "limp home". I'm guessing it would run, but would be waaaaaay down on power. Which may be ok. Frankly, if it can produce enough power for straight and level flight at gross weight its good enough, right?

 

[Toobuilder]

Yep, "limp home". I'm guessing it would run, but would be waaaaaay down on power. Which may be ok. Frankly, if it can produce enough power for straight and level flight at gross weight its good enough, right?

Based upon my dyno testing at LyCon with retarded timing on my PV 540, I suspect the typical Lycoming RV would still perform pretty well @ 10 degrees and a rich mixture. This is even more so with an AV engine like Dan has. I would guess that the loss of power would be “noticeable”, but not alarming.

Dan, you willing to do some takeoff roll timing comparison between 10 degrees and nominal?

 

[DanH]

Based upon my dyno testing at LyCon with retarded timing on my PV 540, I suspect the typical Lycoming RV would still perform pretty well @ 10 degrees and a rich mixture. This is even more so with an AV engine like Dan has. I would guess that the loss of power would be “noticeable”, but not alarming.

Dan, you willing to do some takeoff roll timing comparison between 10 degrees and nominal?

Agree. And yes, a test would be interesting.