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P-Mag "B" Curve Advance Map

Bob,

Unless EmagAir clears this up before I can get around to it, I am going to build a test cell. The mystery is too great to resist!

I need a good working mechanical MAP gauge to make it happen. Anyone want to loan one for the job?

Here is my proposed test cell:

1ea Pmag
1ea Power supply
1ea MAP gauge
1ea Handheld vacuum pump
1ea Variable speed motor with good speed regulation
1ea Handheld tach
1ea Degree wheel
1ea Inductive timing light
1ea Jig to mount this and the plugs to keep from burning out the coils
1ea Computer to run EICAD for serial data monitoring/tweaking settings/etc

What did I miss? Would you change anything?

I think this will be easier than in flight due to not wasting gas, easier to get accurate with the RPM and MAP etc, and it can be video'ed for whoever wants to see it.

My only problem is that I won't be able to do this for at least a month due to having surgery on Monday.....
 
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vac tester

BC,

I have one of these on my mogas tester....

http://www.harborfreight.com/fuel-pump-and-vacuum-tester-93547.html

e-mail me your address.......


Brantel said:
Bob,

Unless EmagAir clears this up before I can get around to it, I am going to build a test cell. The mystery is too great to resist!

I need a good working mechanical MAP gauge to make it happen. Anyone want to loan one for the job?

Here is my proposed test cell:

1ea Pmag
1ea Power supply
1ea MAP gauge
1ea Handheld vacuum pump
1ea Variable speed motor with good speed regulation
1ea Handheld tach
1ea Degree wheel
1ea Inductive timing light
1ea Jig to mount this and the plugs to keep from burning out the coils
1ea Computer to run EICAD for serial data monitoring/tweaking settings/etc

What did I miss? Would you change anything?

I think this will be easier than in flight due to not wasting gas, easier to get accurate with the RPM and MAP etc, and it can be video'ed for whoever wants to see it.

My only problem is that I won't be able to do this for at least a month due to having surgery on Monday.....
Click to expand...
 
Brantel said:
Bob,

I need a good working mechanical MAP gauge to make it happen. Anyone want to loan one for the job?
Click to expand...

Yep I can send you one, email me your address. [email protected].

I also have a rig that I set up on my lathe for testing magnetos. It would work just as well for a PMag. It is simply a plate that fits onto my quick change tool post, with a plate and a hole in it. I bolt the mag onto the plate and put a mag gear in the lathe chuck and position the carriage so the gears mesh. Pretty easy to set up.
 
Share your curve!

Curve removed - MFG information kindly provided in later post!!!
 
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Manometer for MAP

Brantel,

A surprisingly effective and cheap method of pressure measurement is a simple u-tube water manometer. I used to work in development of pressure control equipment, and the manometers were as accurate and reliable as anything else in the lab.

You can set one up with a piece of plywood, some plastic tubing, and a ruler. Very accurate measurements to .1" Hg should be child's play.

M
 
Bob has volunteered a MAP gauge.

The manometer would work fine. I have a nice one I built for ASI/ALT testing.

I like the MAP gauge better just so there are no questions that the data is accurate. Some may not be willing to trust other methods even though they would work fine.
 
All the best to you

Brantel said:
My only problem is that I won't be able to do this for at least a month due to having surgery on Monday.....
Click to expand...

I hope all goes well and you are on the forums again quickly! I appreciate your postings!

Take care,
 
rocketbob said:
...Also worth noting is if one is running mogas with a PMag I would be very cognizant about mechanically retarding the timing as others have done here...
Click to expand...

Just as a data point, I have experimented with auto fuel (mixed with 100LL and straight) in the RV with no performance issues beyond some more stumbling on the ground when hot.

Also note that this is a "high compression" 200 HP angle valve engine and I've run the "advanced B curve" setting on the PMags exclusively for the last 200+ hours.

...and also keep in mind that I operate in the desert Southwest where a "normal" flying day is well over 100 degrees in the summer.

I submit to you that while I'm but one data point, my experience is perhaps one of the most severe you are likely to find. Your caution about owners going into ANY engine modification with their eyes wide open is valid, but in this case, the properly functioning PMag even with the "B curve" is not going to melt the engine down.

That said, I'm retarding back to the A curve out of curiosity. I have hundreds of trouble free hours running advanced, so I should be able to tell very quickly if the airplane "likes" the new setting.
 
Ignorance is bliss?

So the RV has been flying with PMags for several hundred hours in the advanced "B curve" configuration. In fact, I have never run the "A curve" in this airplane. In that time I have come to expect a reliable 165KTAS on 8.5 GPH at my normal cruise altitude of 7500MSL. I have many, many hours seeing these numbers. I have battled with CHT in climb with this airplane, but have largely overcome that problem with baffle mods discussed many times on this forum. Once LOP, CHT's drop to the low 300's, with my hottest up in the mid 300's. Not a great spread, but I'm still working on it.

Anyway, since the cowl was off for a recent prop service, I decided this thread was motivation to pull the timing back to the A curve to see what happens. Just got back from a flight and here's what I found:

(Keep in mind this is ONE data point)

My normal fuel flow of 8.5 now yields no less than 172KTAS. The air was a little bumpy so I did see up to 177 at times, but it seems to settle in at a solid 173. At a mild 52 OAT, the HOTTEST cylinder was 312, with 285 the coldest. Climb temps after a quick turn fuel stop were no higher than 385 on the hottest. This SEEMS to be an improvement, but I didn't climb all the way back up to cruise altitude.

More flights are absolutely required to draw any real conclusions, but the results seem to be encouraging. I didn't think the PMags could get better, but it appears everything about this change is positive. Can't wait to get a pair on my Rocket!
 
Interesting that you picked up speed on the A curve. I would have guessed it would be the other way around.
 
Ryan,
The sweet spot is for the combustion pressure to be highest at 14 degrees after TDC. Deviation away from that (in either direction) reduces power transfer to the crank. Too early and the high combustion pressure is wasted againsts a vertical column of crank, rod and piston (The energy goes into CHT instead). Too late and the piston is falling away too fast to use the expanding gasses properly.

It is pretty obvious (high T.O. CHT and speed improvement from retard) that Toolbuilders engine was advanced too far in both takeoff and cruise configuration, but to his point, more testing is warranted to find his engines sweet spot.
 
Toobuilder said:
My normal fuel flow of 8.5 now yields no less than 172KTAS. The air was a little bumpy so I did see up to 177 at times, but it seems to settle in at a solid 173. At a mild 52 OAT, the HOTTEST cylinder was 312, with 285 the coldest. Climb temps after a quick turn fuel stop were no higher than 385 on the hottest. This SEEMS to be an improvement, but I didn't climb all the way back up to cruise altitude.

More flights are absolutely required to draw any real conclusions, but the results seem to be encouraging. I didn't think the PMags could get better, but it appears everything about this change is positive. Can't wait to get a pair on my Rocket!
Click to expand...

SWEET!!! Is #3 cyl your hottest Michael?? Just curious.
 
I know one data point does is not the final word but I bet David Brown loves Michael's post! I look forward to hearing more about his testing.
 
Brantel said:
I know one data point does is not the final word but I bet David Brown loves Michael's post! I look forward to hearing more about his testing.
Click to expand...

Well, the point remains that variable timing is a good thing in an internal combustion engine. Any engine will respond to "optimal" timing... But the "one size fits all" method of blindly setting a magneto to factory settings can be just as wrong as a poorly set electronic unit.

Car people have been routinely recurving distributors for a half century, and today you can trade digital ignition maps for your motorcycle via email. As airplane people just emerging from the dark ages of locked out magnetos, we just don't have the knowledge base yet.
 
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Michael,

Just a point with the high ambients, the DA goes up with temperature and the engine develops less HP, it does not know the difference, so a really hot day only has part of the effect people think it does.

While your posting is data collected in a less than ideal controlled environment, I am sure that what you observed was not a fluke and you will continue to get similar results.

Your engine longevity will improve also. Whether that matters or not is very hard to know, but it should help in the long term.


Interesting that you picked up speed on the A curve. I would have guessed it would be the other way around.
Click to expand...

You are not the first to be fooled by the OWT of more advance equals more power. The appropriate amount is the appropriate amount. But, like all of us who as a kid thought this was true, you have learned something.
 
Toobuilder said:
Well, the point remains that variable timing is a good thing in an internal combustion engine. Any engine will respond to "optimal" timing... But the "one size fits all" method of blindly setting a magneto to factory settings can be just as wrong as a poorly set electronic unit.

Car people have been routinely recurving distributors for a half century, and today you can trade digital ignition maps for your motorcycle via email. As airplane people just emerging from the dark ages of locked out magnetos, we just don't have the knowledge base yet.
Click to expand...

Michael,

The one size fits all is not a bad way to do it in a aircraft engine. We take off at 2700 (bit less if FP) and we cruise at 2500 and about the same with FP, so the one size is there already.

While LOP operation benefits from a bit of advance, the concept has to be truly understood. I am not sure how many of the folk on VAF have seen PRISM run in real life, but this is the answer we all want. And what is more, it is cylinder independent! Even better!! But it will not be cheap. Success does not bargain with the price however.

Car type and motorcycle ignition maps are for radically different engine applications, 1000-15,000RPM with small diameter pistons etc. Yes they are engines too, but it is like using a hammer as a screwdriver.

As for emerging from the dark ages and having the knowledge base, that exists, it is still experimental, and when the unleaded avgas project is complete, work can then get back to PRISM. By the way the work is not on the technology, its getting the rest of everything sorted, certification too, and spark plugs that need to be a lot less than $1000 each.
 
RV10inOz said:
The one size fits all is not a bad way to do it in a aircraft engine. We take off at 2700 (bit less if FP) and we cruise at 2500 and about the same with FP, so the one size is there already...
Click to expand...

Be careful of using sweeping, simplistic generalizations to make your point. We are talking about optimizing the engine configuration here. The guy who runs his bone stock Lycoming behind a fixed pitch prop is going to have different ignition requirements than the guy with a big bore, high compression engine with ported heads, tuned exhaust and induction mods.

The goal, after all, is to reach peak cylinder pressure a few degrees after TDC. There are many variables involved as you work backward through the combustion process and figure out where to initiate the ignition event to achieve that goal.

Yes, one size fits all magneto timing "works", but so apparently does a PMag with too much advance. And the fact that a mis-timed PMag will STILL significantly outperform a magneto makes it clear there is much to be learned about our simple aircraft engines if we want to optimize our performance.
 
Toobuilder said:
I submit to you that while I'm but one data point, my experience is perhaps one of the most severe you are likely to find. Your caution about owners going into ANY engine modification with their eyes wide open is valid, but in this case, the properly functioning PMag even with the "B curve" is not going to melt the engine down.
Click to expand...

Sitting right in front of me on my desk is a piston from a 300 hour O-360 that has some detonation damage around the crown, and that happened with stock Slicks and mogas. Long story short there was some operator error involved but its still very possible to hurt your motor and not know it until things start snowballing.
 
Pics

Bob,

Can you link to a pic? Would be great to see what it looks like.

I found one: http://flytheengine.blogspot.com/2007_10_01_archive.html

rocketbob said:
Sitting right in front of me on my desk is a piston from a 300 hour O-360 that has some detonation damage around the crown, and that happened with stock Slicks and mogas. Long story short there was some operator error involved but its still very possible to hurt your motor and not know it until things start snowballing.
Click to expand...
 
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rocketbob said:
Sitting right in front of me on my desk is a piston from a 300 hour O-360 that has some detonation damage around the crown, and that happened with stock Slicks and mogas. Long story short there was some operator error involved but its still very possible to hurt your motor and not know it until things start snowballing.
Click to expand...

I don't doubt you for a second Bob, but we also don't seem to have PMag equipped aircraft falling out of the skies, either. Has there ever been a report of PMag induced detonation damage? If there has, it can't be very widespread. And considering the nearly total ignorance many of us are operating these engines, they are still pretty forgiving.
 
rzbill said:
Ryan,
The sweet spot is for the combustion pressure to be highest at 14 degrees after TDC. Deviation away from that (in either direction) reduces power transfer to the crank. Too early and the high combustion pressure is wasted againsts a vertical column of crank, rod and piston (The energy goes into CHT instead). Too late and the piston is falling away too fast to use the expanding gasses properly.

It is pretty obvious (high T.O. CHT and speed improvement from retard) that Toolbuilders engine was advanced too far in both takeoff and cruise configuration, but to his point, more testing is warranted to find his engines sweet spot.
Click to expand...


I see... Well I have been happily running the A curve for nearly 200 hrs. Think I will stay there. Not sure how to find the exact optimal sweet spot...?, perhaps I could pick up a few knots if I did.
 
Toobuilder said:
Be careful of using sweeping, simplistic generalizations to make your point. We are talking about optimizing the engine configuration here. The guy who runs his bone stock Lycoming behind a fixed pitch prop is going to have different ignition requirements than the guy with a big bore, high compression engine with ported heads, tuned exhaust and induction mods.

The goal, after all, is to reach peak cylinder pressure a few degrees after TDC. There are many variables involved as you work backward through the combustion process and figure out where to initiate the ignition event to achieve that goal.

Yes, one size fits all magneto timing "works", but so apparently does a PMag with too much advance. And the fact that a mis-timed PMag will STILL significantly outperform a magneto makes it clear there is much to be learned about our simple aircraft engines if we want to optimize our performance.
Click to expand...

Hang on a minute, in one breath you chastise me for "sweeping simplistic and generalisations" when I was being rather specific about the typical flight regime, and then you go on to say "The guy who runs his bone stock Lycoming behind a fixed pitch prop is going to have different ignition requirements than the guy with a big bore, high compression engine with ported heads, tuned exhaust and induction mods."

All I said was the one size fits all is not a bad way to go when we basically have a static engine parameter being RPM. A small amount of advance at varying powers and LOP is helpful. But think of it this way. Assume a OEM static magneto setting is 25DBTDC is the nominal setting for our imaginary engine. This is a compromise of say (plucking numbers out of a hat) 28 for a LOP cruise at low power and say 22 degrees for takeoff. That is static, the actual will be retarded a few more. So maybe the ideal actual spark firing is say 20 degrees. Along comes another identical engine and let us call the engine BRANTELSLYCOMING for the want of a name, and this engine has an EI that is firing at 30 DBTDC and with not a lot of lag in that electronic number. Where are the sparks firing now compared to where it should.

Just refer back to your own data point.

As for the difference between a compression ratio or turbocharging, well that is why Lycoming and TCM use 25 or 22 or 20 degrees when "static timing" the mags. The TAT TNIO550 found in thousands of Cirrus and Bonanza aircraft are 8.5:1 and hold 30" all the way to FL250 and are timed at 22 degrees. The variables you are thinking are so significant really are not.

The idea of a few degrees after TDC being ideal is the problem you have discovered yourself and so has Brian, generally speaking it is quite a few more than that. Theta PP is best in a range of 14-18 degrees ATDC. When you have an EI that does that for every combustion event on every cylinder you have it nailed. Now where have I seen that before? ;)

Maybe it is a misunderstanding of mine, written posts on the internet do this, but it seems like you are arguing against the logic your data point has provided.
 
One of the funniest threads I've read in here was the 4 or 5 page argument on torque wrenches and how to use them. Pure magic watching obviously smart people with their first torque wrench go tooth and nail over equations and theory...on how to twist a bolt. This thread...is running a close second.

It was said that one size fits all with a standard mag isn't a bad way to go. Then pointed out that Pmag's, even poorly setup outperform mags pretty handily with many flying examples doing just fine. Then it's pointed out that detonation damage has been done to a piston sitting on a desk...though that damage was done by slicks, mogas and pilot abuse...which is supposed to make us worry about Pmags somehow. Add in a very pretty chart that is wrong, a professor selling his classes, competitors buddies trying to steer them some market share and a few "just buy my stuff instead" types and wow this thread really is starting to rival the torque wrench thread. It's not approaching the primer wars yet...but I see potential. This is Internet theatre at its best. Bring on the next chart!
 
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ColoRv said:
Then it's pointed out that detonation damage has been done to a piston sitting on a desk...though that damage was done by slicks, mogas and pilot abuse...which is supposed to make us worry about Pmags somehow.
Click to expand...

Its far more likely for damage to occur with a too far advanced ignition.

Boy Bill you offer some sage advice. Thanks. Glad to know you know so much more than the rest of us.
 
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Please keep it civil guys. Nobody is throwing spears here. This thread is about good civil debate. We are all on the same team, good argument is healthy but there is a fine line between healthy and falling off the edge.

That is where the Internet and forums break down, it seems most threads eventually fall off the edge due to people that are passionate about their point of view cannot communicate in a forum like they can face to face. So much is lost with non face to face communication.

Its all good....and fun, lets just keep it that way, please!
 
Toobuilder said:
we also don't seem to have PMag equipped aircraft falling out of the skies, either.
Click to expand...

That appears to be true. We have moved from earlier catastrophic failures due to sudden addition of high advance (documented here on VAF) to insidious misapplication of too much advance that is possibly (likely?) detrimental over long periods of engine operation. A definite improvement........

While the early failures are now gone, it appears to me as an external observer that the Pmag is entirely too easy for a layman user to misapply. It appears that it CAN be applied properly and work VERY well, but not all users are gearheads that can do it.
 
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Brantel said:
Bob,

Unless EmagAir clears this up before I can get around to it, I am going to build a test cell. The mystery is too great to resist!

I need a good working mechanical MAP gauge to make it happen. Anyone want to loan one for the job?

Here is my proposed test cell:

1ea Pmag
1ea Power supply
1ea MAP gauge
1ea Handheld vacuum pump
1ea Variable speed motor with good speed regulation
1ea Handheld tach
1ea Degree wheel
1ea Inductive timing light
1ea Jig to mount this and the plugs to keep from burning out the coils
1ea Computer to run EICAD for serial data monitoring/tweaking settings/etc

What did I miss? Would you change anything?

I think this will be easier than in flight due to not wasting gas, easier to get accurate with the RPM and MAP etc, and it can be video'ed for whoever wants to see it.

My only problem is that I won't be able to do this for at least a month due to having surgery on Monday.....
Click to expand...

Your list is complete.

I have done these tests with, LSE, Pmag, Electromotive, with an ignition simulator that allows every scenario and degree of testing. All test are base off of crankshaft RPM (4 or 6cyl.).
Here's a pic of the SC-2 display that I was assembling for the show in KOSH/2010. This display provide the information that you are looking for. Timing advance curve and how it is affected by RPM and MAP pressure based off of field elevation in (KOSH) along with other ignition attributes.

IMG_3212_zps110ea379.jpg
 
Thomas,

Well that is way more pretty than anything that I would build....

Cool setup!

I imagine it would be bad form to ask you for your data on a competitors system so I won't do that.

That is an awesome rig however!
 
Thomas you should post a video of your rig, so folks can see what the difference in spark energy is between your product and the EMag which uses a Ford EDIS-4 coilpack. The same coilpacks used on early 90's Ford Escorts.
 
G3i Ignition said:
Here's a pic of the SC-2 display that I was assembling for the show in KOSH/2010.
Click to expand...

My compliments Tom...that's the kind of display that brings me to OSH.

rocketbob said:
Thomas you should post a video of your rig, so folks can see what the difference in spark energy is between your product and the EMag which uses a Ford EDIS-4 coilpack. The same coilpacks used on early 90's Ford Escorts.
Click to expand...

The one in the photo may be an EDIS coil, Standard Motor Products FD487 or equivalent. Recent P-Mags seem to use the EIS coil, SMP FD501 or equivalent. The difference is post style at the high voltage connection. They are, I think, otherwise interchangable.

Let's be fair. They are very reliable coils, and they are used on a wide range of FMC models, worldwide. The only reason I could see to knock the choice would be if E-Mag was sourcing one of the cheap Chinese copies...which I doubt.

I am sure the MSD-based system will display a long stream of sparks. It's what MSD (Multiple Spark Discharge) does, and it is a good thing. Maximum voltage would be limited by the insulation quality of the stock Slick or Bendix coil (they do burn through from time to time, yes?) or breakdown voltage at the plug gap, which is generally a lot lower.

BTW, if I recall correctly the stock Ford EDIS multi-sparks at low RPM for better idle.

ColoRv said:
This is Internet theatre at its best. Bring on the next chart!
Click to expand...

Frankly, I've learned a lot so far. Your results may vary.
 
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For low-revving engines, the larger the coilpack the better. Like cubic inches there's no substitute for more copper in the coil. Of course there are limitations to how much dwell angle it takes to charge a larger coil but at 2700 RPM this isn't a problem for us. Almost all other systems available to us put out at least 2X the spark energy than the Emag coilpack does. That system was simply chosen for the convenience of being able to mount a coilpack in place of the mag.
 
Density altitude

Toobuilder said:
So the RV has been flying with PMags for several hundred hours in the advanced "B curve" configuration. In fact, I have never run the "A curve" in this airplane. In that time I have come to expect a reliable 165KTAS on 8.5 GPH at my normal cruise altitude of 7500MSL. I have many, many hours seeing these numbers. I have battled with CHT in climb with this airplane, but have largely overcome that problem with baffle mods discussed many times on this forum. Once LOP, CHT's drop to the low 300's, with my hottest up in the mid 300's. Not a great spread, but I'm still working on it.
Toobuilder said:
Seems to me to do an accurate cruise comparison with different timing settings you need to compare at the same DENSITY altitude. Air temp can make a big difference.
I'm going to try the same thing ASAP, I've always run the "B" curve (set 2 degrees ATDC) on my 0-360/Cozy IV with good results.
Tim
Click to expand...
Click to expand...
 
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RV10inOz said:
Hang on a minute, in one breath you chastise me for "sweeping simplistic and generalisations" when I was being rather specific about the typical flight regime, and then you go on to say "The guy who runs his bone stock Lycoming behind a fixed pitch prop is going to have different ignition requirements than the guy with a big bore, high compression engine with ported heads, tuned exhaust and induction mods."

All I said was the one size fits all is not a bad way to go when we basically have a static engine parameter being RPM...
Click to expand...

I'm not chastising you David. The problem is that your "typical" flight regime is not all that typical. There are plenty of fixed pitch guys running around at 1500 feet MSL wide open and 2700 RPM, which contrasts sharply with my 8-9k and 22-2300RPM. And yes, fixed magneto timing is a functional compromise between idle, takeoff and cruise. It does work, but variable timing works better.

I will agree that when it comes to ignition timing, "more" is not "better". An engine needs what it needs, period. And further, at one fixed RPM, there will not be a substantial timing difference between a stock and a custom modified Lycoming, but there will definately be a difference. Finding and characterizing that difference is the goal.

It should be obvious that any ignition system running open loop is going to have a fairly crude timing map. We can't possibly optimize every possible operating situation, but we shouldn't reject mere excellence because perfection isn't readily at hand.

I think we're all in agreement that incorrect timing is bad; but it should also be abundantly clear that variable timing is good. IMHO, the answer is to move forward and figure out this new challenge rather than retreat back into the primordial soup clinging to magnetos.
 
Michael,

I think we're all in agreement that incorrect timing is bad; but it should also be abundantly clear that variable timing is good. IMHO, the answer is to move forward and figure out this new challenge rather than retreat back into the primordial soup clinging to magnetos.
Click to expand...

I am glad you said that....it prompted me to recall something, but it is funny how full circle this is. The fixed magneto being old fashioned, what we really need is the pre-historic, the old radials that had a spark shift for in the cruise, and coincidently LOP. One timing or the other.

Funny how old is new again some times. :)
 
RV10inOz said:
I am glad you said that....it prompted me to recall something, but it is funny how full circle this is. The fixed magneto being old fashioned, what we really need is the pre-historic, the old radials that had a spark shift for in the cruise, and coincidently LOP. One timing or the other.
Click to expand...

But also recall they did it to return peak pressure to the mid-teens ATDC, rather than the delayed point of peak pressure typical of current LOP practice.

An EI with the same ability would require two timing maps, switchable in flight, just like the big radial, OR would need to include fuel-air ratio as an ignition map input, meaning electronic fuel injection.

Nice description of operating an R-4360:

http://www.enginehistory.org/r-4360ops1.shtml
 
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REVISED NOTES 1542 hrs, 1/6/2014:
1. Line two of the data chart notes should read ",,,finally settle at 28..." not 35 as it is written.
2. No I don't typically fly a half ball out of trim; only when wrestling with my iPhone camera.

I took a few data points today and present the data below. I limited the collection when it became apparent that the Pmag advance is relatively flat over a nominal range which is easily identified during a data sweep. If you interpret that as I got bored taking data you are correct. This was baseline data as I intend to modify the curve to see if I can do better than the “A” curve. Note that MAP seems to be the dominant driver for the Advance. Also see the Note below the data chart.

Typically you develop a “Purpose of test” statement and then set up your scope/method of test etc to conform with that purpose. My “purpose” was to satisfy my curiosity activated by Brian’s first post and a gentlemanly poke from DanH.


CONDITIONS
Hp 3500' BPE IO-390
OAT 18C AFP fuel injeciton
Pmag Curve "A" Mixture Full Rich
Dual Pmag - -
Data Source: EIC(1) Advance data
GRT EIS(2) MAP/RPM data


30ix852.jpg


1Electronic Ignition Commander (EI Commander, LLC)
2 Grand Rapids Technologies Engine Information System

Below is a shot of the EIC at a low power setting. This device makes data collection and Pmag curve changes a relatively easy task.

2m79je0.jpg


Below is a shot of a relatively high power setting to show the cyl head temps. Since it was only 19 degrees C at 3500' Hp the head temps are not particularly stressed. Note that the altitude on the EFIS is not the Hp used during the data collection.
2ev9qpl.jpg


I didn’t buy the Pmag because of the ability to modify its settings rather I liked its simplicity of installation, operation and self-excitation. I am now becoming more aware and appreciative of what Brad Dement has achieved by providing a tailorable device to a market that has been served exclusively by a single point design. To the Pmags detractors I would say that people like me may have done the system a disservice by treating the Pmag as a plug-and-play device rather than a tailor-to-your-engine system. It is PnP but I don’t think that was the developers’ major objective. To my mind the EIC is indispensable if you like to play around with the systems tailorable features.
 
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Don,

Thanks for doing this with the EI Commander.

Strange how familiar your numbers look when you add the default Adv Shift value of the "B" curve back to your numbers....
 
Don, a question about your data notes, please.

The note says when moving from 24" to 26" the advance values would vary, apparently starting at 28 degrees and eventually settling in at 35 degrees? That seems to be at odds with the 28 degree value recorded in the grid. Could you expand?
 
I would really like to learn more about engine performance and timing theory. Is there a book or something I can purchase. I am running dual pmags happily for 200 hrs as the plug n play mode curve A. From this thread, the one thing I have learned is I may not be achieving the best performance I could be getting. I have also learned I know very little...

I may even break down and buy the EI commander so I can fine turn my timing, but before fine tuning I do want to make sure I have a good crasp of what I am doing. So again, I am interested in trying to learn more..what books,DVDs...etc should I look for or are recommended.?..or is it just experience is the best teacher.
 
Ryan,

There is plenty of info about tuning automotive engines out there to help with the theory. But in the real (automotive) world, many of us learned by making some changes and then making a quarter mile pass at the dragstrip. True, you could get close to the baseline by copying what others have done, but in the end, the car would pick up or lay down based on what it liked or didn't like. The "rich" guys would use a dyno to tune, but the dragstrip was the best in situ tuning aid we had available.

In contrast, we have very little data to go on in the aviation world, but in the end it will still come down to in situ testing. Dyno time is still expensive, and we can't fly and test with the same accuracy as a car on a dragstrip, but we're going to have to work with what we have. Its going to take a bunch of collective avgas, but eventually we will be able to find our individual engine's "happy place".

If I did indeed pick up some power by going from the advanced curve back to the baseline, then a slight further retard should show a benefit or a detrement. If it picks up or lays down, that tells you which way to go.
 
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DanH said:
Don, a question about your data notes, please.

The note says when moving from 24" to 26" the advance values would vary, apparently starting at 28 degrees and eventually settling in at 35 degrees? That seems to be at odds with the 28 degree value recorded in the grid. Could you expand?
Click to expand...

Good catch Dan. It should read "settling in at 28..." Also please note that I don't typically fly out of trim only when wrestling with my iPhone camera in the cockpit. Thank you for not mentioning it although I am confident it didn't go unnoticed.
 
APACHE 56 said:
Good catch Dan. It should read "settling in at 28..." Also please note that I don't typically fly out of trim only when wrestling with my iPhone camera in the cockpit. Thank you for not mentioning it although I am confident it didn't go unnoticed.
Click to expand...

Thanks Don.

It's an interesting set of timing values in three areas.

The high manifold pressure, high RPM range is 3 degrees more advanced than the OEM compromise fixed timing for an parallel valve, and 8 more than the OEM timing for an angle valve. For that reason alone I would again suggest a modified B map to get a 20 degree base or less for your angle valve 390.

The timing values for these upper power settings vary with manifold pressure while ignoring the effect of RPM. Lightspeed does it the same way. Electroair does the opposite; they ignore manifold pressure and vary timing with RPM. All three switch to a matrix at lower power settings.

The P-Mag 24" Hg values are quite advanced compared to the others. For example, check it against the Electroair map in post #105:

24" Hg P-Mag vs Electroair
@2200 RPM 36 vs 23.4
@2300 RPM 35 vs 23.9
@2450 RPM 35 vs 24.5 (aprox)
@2700 RPM 35 vs 25.7

Same is true, to a lesser degree, for the 22" line.

Observations only, no conclusions.
 
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The Electroair is certified/STC'd for 4 cyl lycs so it must have passed some kind of "certification" process?
 
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