Effect of Ignition Timing on TAS/EGT/CHT when WOT & LOP

I am trying to set the record for the most TLA in a thread title.

I have dual PMags and an EI Commander. Today I did a cheap and cheerful test to look at the effect of ignition timing in the cruise. All testing was done at 10,000' PA, 5 deg C OAT, WOT, Prop 2500 RPM and leaned to 25F LOP. After this the only thing I changed was the maximum allowed advance.

The way the engine has been configured to date is Max RPM 3072, Max Advance 35 deg, 0 deg advance shift.


I made a change to max advance (reduced in 2.8 deg steps) and sent the change to both PMag simultaneously. My engine has been happy with 36 deg advance till now so I was not concerned about sending it less advance.

The actual advance reported is always 1.4 deg more than the Max Advance you program in the EI Commander map. What I show below is the advance as displayed by the EI Commander, which is 1.4 deg more than I asked for.

At the very left of the picture you see the fuel flow reducing as I lean the engine. From this point on throttle prop and mixture are fixed and all changes are a function of advance only.

Effect of ignition timing, reading left to right, the step changes in EGT on the top graph are where the timing changes are made.

36.4 deg, 182 KTAS, time 28 - 31
33.6 deg, 180 KTAS, time 31 - 34:30
30.8 deg, 176 KTAS, time 34:30 - 38
28.0 deg, 173 KTAS, time 38 - 42
25.2 deg, 171 KTAS, time 42 - 44:30
22.4 deg, 170 KTAS, time 44:30 - 48
36.4 deg, 182 KTAS, time 48 -

Timing is then reset back to 36.4 deg and this is shown where the EGT rapidly drop again on the right hand side of the graph.

The CHT's on my aircraft always take about 5 minutes to stabilize after a power/mixture change and I did not wait that long, so the exact effect on CHT could be a little different to what I summarize below.

In general as I reduce advance from 36.4 deg I get the following changes:

KTAS reduces by ~ 1 KTAS / deg advance
EGT increases by ~ 10 F / deg advance
CHT reduces by ~1 F / deg advance

If you get the ignition timing badly wrong it can hurt the engine. If you feel like experimenting I suggest you buy a bore scope before hand and take photos of all your pistons and valves so you have a baseline. This way if anything goes wrong you will be able to make a better determination of potential damage done. Do any timing changes high enough and close enough to a nice long runway so that you can easily conduct a power off landing. Make sure you are proficient in power off landings. Educate yourself as to the likely/expected outcomes of any ignition timing change so you can judge if the outcome of a change is normal. Be proficient in the use of the device that you are using to make changes so that you don't spend too much time eyes inside. Try to preserve a proven map/setting that you can return to quickly if the one you just tried turns out to be inappropriate. Although your engine might be broadly similar to mine there are no doubt subtle differences, so what works for mine might kill yours. The data shown is just meant to be one of many ways to do an ignition timing test, it is not a suggested setting for your engine.

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Cheers
Nige

Your results are as expected. As timing advance increases towards optimum, more of the energy (i.e. Heat) remains in The chamber doing work instead of going out the exhaust. This reduces eGT and increases CHT. The increased work increases HP and ultimately TAS.

nigelspeedy said:

The actual advance reported is always 1.4 deg more than the Max Advance you program in the EI Commander map. What I show below is the advance as displayed by the EI Commander, which is 1.4 deg more than I asked for.

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Awesome info, many thanks for it. Would you also have the fuel flow for each of those settings to see who the speed reduction is reflected in the fuel consumption?
I have recently got a second PMAG and EIC but still working out some bugs. One thing that I saw after installing the second PMAG and now both on version 40 and timed right at TDC, I noticed higher CHT as well as EGT. I programmed my EIC to reduce the timing it by -1.4 (not max advanced) and that seem to have helped.

Can you please elaborate on the above statement as why that is?

Nigel, this is a 180 horse parallel valve?

Fuel Flow

The Fuel Flow was constant at 8.4 gph, shown as the slightly noisy but essentially flat blue line on the top graph, scale on the right hand side. All changes are due to timing only.

Putting in a - offset reduces the advance across the whole map. Think of offset as sliding the sloping line left/right. The max advance sets how high the slope can go. Unfortunately you cant change the slope though.

The engine is a parallel valve IO-360 stroked to 380, 10:1 compression, dual PMags, and the heads were ported/polished. Really feels as though it likes a good bit of advance. Down around 25 deg it just feels sluggish and subjectively feels ever so slightly less smooth but I don't have any data to support that.

I also did a test on the advance on idle quality but I haven't crunched that yet.

Cheers

Nige

Timing Offset Effect

By changing the offset in a negative way you have less advance. I.e. the spark happens latter, so peak pressure happens further after TDC. Less work inside the cylinders so lower CHT, more wasted out the exhaust so higher EGT.

Was your idle smoother?

Cheers

Nige

Interesting data. With this and what TooBuilder published when testing timing on his Rocket a couple months back, I hope people can now see the real benefits of EIs with adjustable timing curves compared to running 24-25 degrees fixed timing across the board.

Thanks for posting!

Our customers are seeing a similar sweet spot at altitude with similar engine specs at around 35 degrees true timing.

nigelspeedy said:

By changing the offset in a negative way you have less advance. I.e. the spark happens latter, so peak pressure happens further after TDC. Less work inside the cylinders so lower CHT, more wasted out the exhaust so higher EGT.

Was your idle smoother?

Cheers

Nige

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I could not detect any effect on my idle and/or smoothness. Prior to V40, I had set my timing a couple of degrees aft TDC and this was just to duplicate that. I was really surprised that both my CHT and EGT were higher, compared to the past, without the -1.4 degree (A Curve) and set at TDC. Also, the way I understood the EIC, which I still need to read more on it, setting this way does not effect the max advance. Feel free to set me right here

V 40 changes

My understanding is that one of the changes in the V40 software update to the PMags was a retard to timing when the engine was at very low RPM when being turned over on the starter motor. So with V40 the plugs should fire a few (unsure how many, but I think about 4 deg) deg ATDC to avoid any issues of kickback with a light weight flywheel and/or prop. Once the engine is running faster than a couple of hundred RPM (again unsure exactly how fast) the timing then transitions to BTD and at idle speed gives about 19.6 deg BTDC.

Putting in an advance shift indirectly affects the maximum advance under some circumstances. For example if you wanted to allow 40 degrees of maximum advance but you also put in -10 deg of advance shift you may never be able to get to a MAP & RPM condition that would provide 40 deg total. This is because you can't adjust the sensitivity of the PMag advance curve to MAP & RPM, or put another way you can't adjust the steepness of the slope of the advance curve. If you have a maximum advance set, changing the timing shift will not result in an exceedance of the maximum you have set, but a negative offset may result in never being able to reach the maximum.

My engine with 0 deg timing shift idles at 700 RPM and 23.8 deg advance. If I put in a -1.4 deg shift the idle quality improves with 21.0 deg advance. The down side is that inflight at altitude I can't get as much as 36 deg maximum advance which the engine likes for best LOP cruise performance. So given that it spends much more time cruising than idling I may have to sacrifice a little smoothness at idle to allow the PMags to give the large advance necessary for best cruise performance. The ability to fully control the timing curve would be an advantage over the current PMag with EI Commander configuration.

Cheers

Nige

I am impressed, thanks for posting.

Great info. Thanks for sharing.

Nigel,
Thanks again for a good write up and explanation. I shall start experiment with different setting to see where the sweet spot is for my engine.

I echo the thanks of others. This quantifies beautifully what many of us have believed for some time .... the very reason we opted for EI.

Nigel,

Your testing jives with mine, and it is no surprise that you are slower when you pull timing out in a LOP condition. However, as my testing also indicates, the slope of the “HP/Timing curve” (for lack of a better name) gets steeper as the mixture gets leaner. This indicates to me that you should try to advance the timing a few degrees as well. If it slows down, then you have established your optimum timing advance for LOP. If it picks up some speed then falls off, at least you know where the engine wants to be.

Now, there are a couple of issues with a “locked” advance curve scenario which I did not realize until I started playing with total adjustability of the CPI system:

1. Even if you are correct and your current max advance is “optimum” for your LOP condition, then it is going to be about 3-4 degrees TOO advanced for anything richer than LOP.

2. If you drag the whole curve far enough advanced to run LOP efficiently, then you also can’t pull timing out for TO. As I have found, you can actually RETARD timing from the data plate value at high power settings with no loss of power. If you are running in high ambient temps and/or big compression, pulling timing out at TO power buys you a bunch of detonation margin.

EI in general buys you a performance advantage over magnetos. There are very few who will dispute this. But what our testing is just bringing to light is how wide and varied the actual advance curve requirements are for each engine configuration and mission. I predict that the ability to independently manipulate timing for start retard, idle, RPM, MP and yes, even mixture (ROP/LOP) is going to become the new minimum requirement for aircraft ignition systems.

Toobuilder said:

. . .But what our testing is just bringing to light is how wide and varied the actual advance curve requirements are for each engine configuration and mission. I predict that the ability to independently manipulate timing for start retard, idle, RPM, MP and yes, even mixture (ROP/LOP) is going to become the new minimum requirement for aircraft ignition systems.

Click to expand...

Well now! Sign me up for one of these! Of course, the auto industry has been running this type of EI for 20-30 years now and they continue to get more and more detailed in their configurations with every new iteration. Of course in that world they are doing this with computers and specific F/A ratio computer code configurations. Something the aviator world has balked at emphatically:

"THE ONLY COMPUTER I TRUST AROUND MY AIRPLANE IS THE ONE BETWEEN MY EARS!"

Is an attitude I have heard every since I started flying. The reality is, reliability not withstanding, this is where we should be heading.

Flame suit on.

Live Long and Prosper!

Thanks for input Mike

Mike I agree with your points.

As I look closer it seems that the Mags and EI Commander is still going to be a compromise solution. Albeit a much better compromise than traditional mags with fixed timing. A 7% TAS advantage on the same fuel flow is nothing to be sneezed at when coupled with the other advantages of electronic ignition. But you are right it would be nice to have better control/authority over the ignition timing map to be able to lower the advance for idle and high power conditions and still be able to get the large advance needed for LOP. To do the ROP/LOP adjustments I guess we will have to follow the automotive path and use exhaust oxygen sensors.

If I can get some good data it will be interesting to see if Brad at PMags is open to the idea of altering the base map to allow a greater spread of advance across the operating range.

You are right about not knowing if 36 deg is the best until I try more and see that it gets worse. Out of interest what is the maximum timing advance you have given your engine?

I am planning on repeating the test ROP and also using a series of level accels to test the affect of timing at high power ROP and low altitude in addition to using the max speed as the measure.

Cheers

Nige

since you're being scientific, you should do some tests of WOT cruise vs reduced manifold cruise

showing temps/TAS- we still have a lot of guys on here dropping the power for a climb

nigelspeedy said:

You are right about not knowing if 36 deg is the best until I try more and see that it gets worse. Out of interest what is the maximum timing advance you have given your engine...

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In my typical cruise condition (which approximates your testing here), my engine peaked at 33. I went out to 35, but the declining HP trend was clear so I saw no need to go further.

That said, my RPM and MP settings will allow up to 40 degrees in some low power high RPM circumstances (such as a descent into the pattern). The 40 degrees is neither desired nor harmful, it's simply a byproduct of the composite (RPM and MP) timing. That aspect can be tuned out with map manipulation, but I'm still focusing on the more critical areas of the envelope.

RVbySDI said:

Well now! Sign me up for one of these!...

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Give Ross a call. He's leading the pack right now.

EIC T/O & Climb as well as Cruise Map

In hindsight it would not be that hard to meet the dual requirements of takeoff/climb/ROP and cruise/LOP operations.

Define one map with -2.8 deg timing shift and a max of 30 deg, and another with 0 deg timing shift and a max of 35 deg. Numbers here just as an example not a recommendation.

On the EICommander it takes about 6 button presses to select and load a new map, so a little clumsy but you would only have to do it twice per flight (top of climb and top of descent). A single switch would be nicer and having it done automatically would be ideal.

Certainly more testing to be done as time allows.

Cheers
Nige

Why drop power for a climb?

Brian,
What do you mean by guys dropping power for a climb? Do you mean reducing the throttle to prevent being over square?

My home airport it 4000' so WOT I only just get a little over 25" MAP on takeoff and my general mode of operation is to open the throttle fully on takeoff and I leave it there until top of descent. Even when I takeoff at lower altitude airports I leave the throttle fully open and pull the prop back to 2500 RPM. So for the first few thousand feet I will be a couple of inches over square. A quick look at a Lycoming power chart shows that there is quite a large region of over square operations within the area marked as acceptable for continuous operations.

Cheers
Nige

nigelspeedy said:

...In hindsight it would not be that hard to meet the dual requirements of takeoff/climb/ROP and cruise/LOP operations...

Click to expand...

Well, I think you can get closer with this scheme, but most EI's are looking to give data plate value at takeoff. And I think that is likely too much advance.

I believe that the fixed value established by the engine OEM (25 degrees, for example) is a compromise setting. It provides acceptable idle and takeoff, but the real target is ROP cruise. Since the OEM is looking to optimize the most significant operating condition (cruise) and can only pick one timing value, then all other conditions suffer somewhat.

My testing indicates that you can significantly retard the timing (compared to the data plate) at high power settings with no discernible loss in power. As a result, my map now retards timing at high MP settings. My data plate specifies 25 degrees, but I'm now seeing 21 or so up here in the high desert, and even less down at sea level. I'm simply trying to buy back some detonation margin. Probably not much of a chance of detonation with my 8.5 CR, but certainly something to pay attention to for the guys running big compression.

nigelspeedy said:

Brian,
What do you mean by guys dropping power for a climb? Do you mean reducing the throttle to prevent being over square?

My home airport it 4000' so WOT I only just get a little over 25" MAP on takeoff and my general mode of operation is to open the throttle fully on takeoff and I leave it there until top of descent. Even when I takeoff at lower altitude airports I leave the throttle fully open and pull the prop back to 2500 RPM. So for the first few thousand feet I will be a couple of inches over square. A quick look at a Lycoming power chart shows that there is quite a large region of over square operations within the area marked as acceptable for continuous operations.

Cheers
Nige

Click to expand...

Not answering for Brian, but outside of "over square" there is also an issue of over heating during climbs. Many have to throttle back due to over heating cylinders during extended climbs. It could be this is the issue instead of running "over squared".

Personally, I believe any discussion about operating "over square" should be left to the round engine forums and does not relate very much to our horizontally opposed "small" engines.

Toobuilder said:

I'm simply trying to buy back some detonation margin. Probably not much of a chance of detonation with my 8.5 CR, but certainly something to pay attention to for the guys running big compression.

Click to expand...

Just as a datapoint, running 91 premium with ethanol for testing purposes, I'm fairly certain I experienced one episode of detonation lasting a few seconds until I pulled it back. I saw my #4 CHT rising at a rate of 8-10 degrees per second through 425, got it stopped at 437 with full rich and pulling power back to 18" MAP, this occurred on a max performance hot climb at about 4000' with 80F OAT. I have not had anything like this occur on 100LL, I'm running 8.5CR with one mag and one Lightspeed II, Bendix injection and C/S prop at 2650 rpm.

It's good to know where the edges are.

nigelspeedy said:

My home airport it 4000' so WOT I only just get a little over 25" MAP on takeoff and my general mode of operation is to open the throttle fully on takeoff and I leave it there until top of descent. Even when I takeoff at lower altitude airports I leave the throttle fully open and pull the prop back to 2500 RPM. So for the first few thousand feet I will be a couple of inches over square. A quick look at a Lycoming power chart shows that there is quite a large region of over square operations within the area marked as acceptable for continuous operations.

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Example below (We now return you to an excellent conversation).

Thanks Dan

Exactly the chart I was referring to.

If you are reducing power during takeoff to keep the cylinders cool (I use 400F as a maximum) I think in the long run you would be better off perusing better cooling/baffling and or climbing at a higher airspeed. The typical RV mission does not have a get to altitude as fast as possible requirement (Vy) so try climbing at a higher airspeed. About 1.2 Vy will maximize climb rate and airspeed and keep cylinders cooler.

Cheers

Nige

airguy said:

Just as a datapoint, running 91 premium with ethanol for testing purposes, I'm fairly certain I experienced one episode of detonation lasting a few seconds until I pulled it back...

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Interesting you bring this up as I would like to look into mogas, and the adjustability of the CPI makes it a more viable option.

Toobuilder said:

Interesting you bring this up as I would like to look into mogas, and the adjustability of the CPI makes it a more viable option.

Click to expand...

I second this! It seems that with enough timing pulled in the right places, this should be possible.

Would it be possible to run 93 oct mogas with a 9:1 CR with a CPI mapped to retard timing somewhat at high power and take off at high MP and appx 2400 rpm and still advance it for high altitude LOP cruse?

wilddog said:

Would it be possible to run 93 oct mogas with a 9:1 CR with a CPI mapped to retard timing somewhat at high power and take off at high MP and appx 2400 rpm and still advance it for high altitude LOP cruse?

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Yes, no problem, simply enter retard values at the higher manifold pressures and set your advance switch window to whatever you want. Throw the switch after you set up LOP cruise at altitude. After setup, it's all automatic except for throwing the advance switch when you run LOP and turning it off when you descend and go ROP.

This strategy will allow you to make good power down low and maximize efficiency up high LOP with maximum detonation margins on mogas.

wilddog said:

Would it be possible to run 93 oct mogas with a 9:1 CR with a CPI mapped to retard timing somewhat at high power and take off at high MP and appx 2400 rpm and still advance it for high altitude LOP cruse?

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I think there are two questions here: One is "Will a 9:1 aircraft engine run on 93 octane"?

and the other is

"Can the CPI support a custom advance schedule to both retard and advance based on RPM/MAP"?

I don't know the answer to the first, but the second one is an easy "YES".

We talk about "advance curves", but I'd like to point out that the CPI is programmed in 100 RPM increments AND .6 (IIRC) inch MP increments. At the end of the day, you have a "curve", but if (for some reason) you wanted to program it with 25 degrees of advance at 2400RPM and then drop it back to 25 degrees of RETARD at 2600RPM, and then 0 at 2700, it will do exactly that. Same with MP. if you want it advancing 5 degrees at 23.4 inches, then retard 10 degrees at 24 and then back to 10 degrees advance at 24.6 inches, it will comply with your request. And then there is the advance switch which will simply add any preset value right on top of the current RPM/MP composite.

In short, there is no preset curve that you "shift" slightly with the CPI - you plug in the requirements right from the face of the brain box. If you want a curve that looks like a sine wave, saw tooth, a copy of the other manufacturers curve, or perfectly flat, that's what the CPI will give you.

rv6ejguy said:

Yes, no problem, simply enter retard values at the higher manifold pressures and set your advance switch window to whatever you want. Throw the switch after you set up LOP cruise at altitude. After setup, it's all automatic except for throwing the advance switch when you run LOP and turning it off when you descend and go ROP.

This strategy will allow you to make good power down low and maximize efficiency up high LOP with maximum detonation margins on mogas.

Click to expand...

Thanks,Ross,
Could This be done with a single CPI and one mag with the mag timing set the same as the CPI at high power ,say 22 BTDC. Then at LOP it would have CPI spark way before the mag spark?? I guess it would be better to run dual electronic ignition, but I would like to avoid a back-up battery.
Bill

wilddog said:

Thanks,Ross,
Could This be done with a single CPI and one mag with the mag timing set the same as the CPI at high power ,say 22 BTDC. Then at LOP it would have CPI spark way before the mag spark?? I guess it would be better to run dual electronic ignition, but I would like to avoid a back-up battery.
Bill

Click to expand...

Yup. A number of our customers still want to run one mag. Just have to run a few more degrees advance on the CPI to get roughly the same effect.

A 4 cylinder CPI draws only about 2 amps at 2500 rpm.

And I measured my 6 cylinder at less than 1.7 amps at takeoff power (2700)

nigelspeedy said:

I am trying to set the record for the most TLA in a thread title.

I have dual PMags and an EI Commander. Today I did a cheap and cheerful test to look at the effect of ignition timing in the cruise. All testing was done at 10,000' PA, 5 deg C OAT, WOT, Prop 2500 RPM and leaned to 25F LOP. After this the only thing I changed was the maximum allowed advance.

The way the engine has been configured to date is Max RPM 3072, Max Advance 35 deg, 0 deg advance shift.


I made a change to max advance (reduced in 2.8 deg steps) and sent the change to both PMag simultaneously. My engine has been happy with 36 deg advance till now so I was not concerned about sending it less advance.

The actual advance reported is always 1.4 deg more than the Max Advance you program in the EI Commander map. What I show below is the advance as displayed by the EI Commander, which is 1.4 deg more than I asked for.

At the very left of the picture you see the fuel flow reducing as I lean the engine. From this point on throttle prop and mixture are fixed and all changes are a function of advance only.

Effect of ignition timing, reading left to right, the step changes in EGT on the top graph are where the timing changes are made.

36.4 deg, 182 KTAS, time 28 - 31
33.6 deg, 180 KTAS, time 31 - 34:30
30.8 deg, 176 KTAS, time 34:30 - 38
28.0 deg, 173 KTAS, time 38 - 42
25.2 deg, 171 KTAS, time 42 - 44:30
22.4 deg, 170 KTAS, time 44:30 - 48
36.4 deg, 182 KTAS, time 48 -

Timing is then reset back to 36.4 deg and this is shown where the EGT rapidly drop again on the right hand side of the graph.

The CHT's on my aircraft always take about 5 minutes to stabilize after a power/mixture change and I did not wait that long, so the exact effect on CHT could be a little different to what I summarize below.

In general as I reduce advance from 36.4 deg I get the following changes:

KTAS reduces by ~ 1 KTAS / deg advance
EGT increases by ~ 10 F / deg advance
CHT reduces by ~1 F / deg advance

If you get the ignition timing badly wrong it can hurt the engine. If you feel like experimenting I suggest you buy a bore scope before hand and take photos of all your pistons and valves so you have a baseline. This way if anything goes wrong you will be able to make a better determination of potential damage done. Do any timing changes high enough and close enough to a nice long runway so that you can easily conduct a power off landing. Make sure you are proficient in power off landings. Educate yourself as to the likely/expected outcomes of any ignition timing change so you can judge if the outcome of a change is normal. Be proficient in the use of the device that you are using to make changes so that you don't spend too much time eyes inside. Try to preserve a proven map/setting that you can return to quickly if the one you just tried turns out to be inappropriate. Although your engine might be broadly similar to mine there are no doubt subtle differences, so what works for mine might kill yours. The data shown is just meant to be one of many ways to do an ignition timing test, it is not a suggested setting for your engine.

[/URL][/IMG]

Cheers
Nige

Click to expand...

Nigel,

I'm in the process of evaluating Electronic ignitions to put on my RV8 and ran across this thread, great info and thanks for posting it. My question to you is when you say "My engine has been happy with 36 deg advance till now so I was not concerned about sending it less advance" What defines "happy" I assume egt's, cht's, smoothness etc are in normal range but hate to assume so thought I would ask. Your increase in speed by advancing the timing 10 degrees in this setting is amazing and I am wondering by doing this what the internal cylinder pressure might be with the power settings you mention and the advanced timing?

agflyboy said:

Your increase in speed by advancing the timing 10 degrees in this setting is amazing and I am wondering by doing this what the internal cylinder pressure might be with the power settings you mention and the advanced timing?

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Higher than with the less advanced timing checked in this test.

Thought exercise: Let's assume we plot speed against timing for a fixed RPM with a CS prop. If Nigel had gone the other way, advancing beyond 35 BTDC, the advance line would be a simple linear upslope. The speed line may or may not upslope a bit more, but then it would curve into a flat spot with increasing advance, and with even more advance the speed line would decline.

Meanwhile, if we plotted in-cylinder pressure, it would keep rising as the speed fell off at very high advance. Peak pressure would be arriving very early, with the piston at or before top dead center. At TDC the piston has no mechanical leverage on the crank, and thus cannot produce useful power. Same energy, very small combustion space, no leverage means lots of pressure, lots of CHT, but no power.

Be sure to understand that Nigel's numbers were taken at 25 LOP, where combustion is slow. With a fast burning best power mixture (about 125-150 ROP), 35 degrees would be too advanced. That's why many of us are interested in dual map systems (flip a switch to select an optimum timing map for rich or lean operation), which currently means the SDS CPI, EDIS/Megajolt, or Megasquirt.

Happy how to know?

G'day Kevin,

I based my simple assessment of 'happy' on moderate CHT's and smooth running. I don't worry about the magnitude of my EGT's, just their relationship to peak. I am just finishing up a lengthy ignition timing experiment and one obvious outcome is that it is better to err on the side less rather than more advance. More to follow.

Cheers

Nige

G'day Kevin,

I based my simple assessment of 'happy' on moderate CHT's and smooth running. I don't worry about the magnitude of my EGT's, just their relationship to peak.

I am just finishing up a lengthy ignition timing experiment and one obvious outcome is that it is better to err on the side less rather than more advance. I cant really comment on cylinder pressure or power as I did not measure it directly. Oh to have a nicely instrumented dyno. I agree with Dan's comments on the likely changes though. More detailed analysis of experiment to follow.

Cheers

Nige

Nige,

Thanks for the reply and looking forward to the results of your experiment and additional info. I posted on Beechtalk about advanced timing LOP operation hoping one of the APS guys that have a test stand and have run these test before would reply. I received a response from George Braly, sounds like normally aspirated, up high, LOP a guy will be alright. I agree to err on the less advance side.. I went through their course a couple years ago and got to see the engine on the test stand and some of the data they can collect was pretty neat.

Thanks,

Kevin

That BeechTalk thread :http://www.beechtalk.com/forums/viewtopic.php?f=37&t=129529

rv6ejguy said:

Yes, no problem, simply enter retard values at the higher manifold pressures and set your advance switch window to whatever you want. Throw the switch after you set up LOP cruise at altitude. After setup, it's all automatic except for throwing the advance switch when you run LOP and turning it off when you descend and go ROP.

This strategy will allow you to make good power down low and maximize efficiency up high LOP with maximum detonation margins on mogas.

Click to expand...

This is a great thread.


You're at cruise altitude with the LOP switch on and you descend but for get to flip the LOP switch back to ROP. What happens?

Thank you,

Chkaharyer99 said:

This is a great thread.


You're at cruise altitude with the LOP switch on and you descend but for get to flip the LOP switch back to ROP. What happens?

Thank you,

Click to expand...

The software negates the LOP switch input above 25 inches MAP as a safety.