I understand the benefits of EI. MY question is, if obtaining max horsepower at wide open throttle from a high performance (200 hp or more 10:1 compression etc.) io-360 is the only consideration, then how much horsepower gains can you expect vs. regular mags? Has there been any actual dyno data to support? Second question is, if you are after horsepower wot then is any Ei product doing better than the competition? I read a lot about the racers etc. using Lightspeed ignitions.
Van's Air Force
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Horsepower gains from Electronic Ignition
- Thread starter jhiggins
- Start date
ROP down low, WOT minimal if any gains with EI alone.
Up high, LOP, some reasonable gains to be had with EI compared to fixed mag timing which isn't optimized for these conditions.
Most EIs have canned timing curves which won't suit all engines (especially modified ones) under all conditions. Look for one that has easy, user adjustable timing curves if this is your quest.
There is only one system which comes standard, user programmable without add-ons and gives total flexibility for custom MAP/ RPM curves, cranking retard and easy LOP advance.
Up high, LOP, some reasonable gains to be had with EI compared to fixed mag timing which isn't optimized for these conditions.
Most EIs have canned timing curves which won't suit all engines (especially modified ones) under all conditions. Look for one that has easy, user adjustable timing curves if this is your quest.
There is only one system which comes standard, user programmable without add-ons and gives total flexibility for custom MAP/ RPM curves, cranking retard and easy LOP advance.
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Carl Froehlich
Well Known Member
Electronic igntion is not so much about HP gain. It is about having the timing advance when high and LOP to get better fuel efficiency. This week I cruised from Ocala Florida to Shannon Virginia at 180kts TAS burning 8.4 gph at 7500’ (RV-8A, 180HP IO-360, dual pMags).
Side benefits include:
- Use of much cheaper auto plugs
- Easy starting
- Little if any fouled plug issues
- Simple to install, time and maintain, with very good reliability (at least for pMag)
Carl
Side benefits include:
- Use of much cheaper auto plugs
- Easy starting
- Little if any fouled plug issues
- Simple to install, time and maintain, with very good reliability (at least for pMag)
Carl
N941WR
Legacy Member
Jim,
Ross and Carl are correct. You don't gain HP so much as an EI allows the engine to run at the most efficient timing for the power setting.
It really doesn't matter which EI you run because they all allow the timing to advance based on MAP and RPM. The goal is to have maximum cylinder pressure at 13 to 14 degrees after TDC and the advance feature allows this to happen.
An example I like to use is that if you have fixed timed magnetos and spend an hour doing takeoff's and landings and then do the same thing in the same conditions with electronic ignitions, your fuel burn should be the same.
However, if you spend an hour flying at altitude with the same power settings but with two different ignitions, the EI will get you there faster for the same fuel burn because it is more efficient (or you can go the same speed for a reduced fuel burn).
I left you a message, give me a call and I'll be happy to answer any questions you may have.
Here is a talk I gave on Electronic Ignition basics to this group earlier this year on the subject.
Ross and Carl are correct. You don't gain HP so much as an EI allows the engine to run at the most efficient timing for the power setting.
It really doesn't matter which EI you run because they all allow the timing to advance based on MAP and RPM. The goal is to have maximum cylinder pressure at 13 to 14 degrees after TDC and the advance feature allows this to happen.
An example I like to use is that if you have fixed timed magnetos and spend an hour doing takeoff's and landings and then do the same thing in the same conditions with electronic ignitions, your fuel burn should be the same.
However, if you spend an hour flying at altitude with the same power settings but with two different ignitions, the EI will get you there faster for the same fuel burn because it is more efficient (or you can go the same speed for a reduced fuel burn).
I left you a message, give me a call and I'll be happy to answer any questions you may have.
Here is a talk I gave on Electronic Ignition basics to this group earlier this year on the subject.
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N941WR
Legacy Member
The trick with getting the maximum performance is testing and configuration.
Some racers use Lightspeed, some SDS, some P-mags, and others fixed timed magnetos.
Last year I helped one Reno racer gain 20 knots with getting his timing set properly. That was a bit over the top but goes to show how setting the timing wrong can have a BIG impact on performance.
I found out that many Reno racers run fixed timed mags but they spend a LOT of time figuring out what that optimal time is for their engine and race conditions. They would adjust their mags on race day.
Electronic ignitions (I'm writing this so as to avoid recommending one EI over another, lest this thread drop into another brand X is best) all work pretty much the same. They allow for advance as power drops off with altitude and throttle setting. Full throttle with high manifold pressure and they should all run the timing configured to give the best performance at the current density altitude and engine configuration.
Beyond that, it comes down to what you want; full access to the timing map, internal generator vs. battery backup, etc. This is like the Chevy, Ford, Dodge, Toyota, Nissan argument.
In short, any of the available ignitions will give you good service, if installed and configured correctly. There is no "Plug and Play" EI system.
FasGlas
Well Known Member
There's more to this story. Timing is not the entire story for producing horse power. How efficient the spark is also creates horse power. A faster and more complete the air/fuel charge is burnt by the spark the more horse power will be created. If the piston is already heading down while the fuel is burning you are not creating horse power. Energy, duration and accuracy will make a big difference. I've never put my engine on a dyno but when I removed one Bendix mag and replaced it with one ElectroAir I saw a dramatic increase in WOT performance. That was many years ago. Now I'm running two ElectroAir's but no real performance increase, mostly smoother. Low energy EI's are just mags with variable timing. EI's are not all the same, this is a fact.
You don't know what advance the EI was delivering and the spark either ignites the mixture or it doesn't. Ignition probability is superior with most EIs because there is more spark energy especially sick rich and at low rpms where mag spark is weaker but this has little to no effect on naturally aspirated, low rpm, low specific output and low CR Lycomings running near best power mixture in cruise or full power. People like to talk of a "hotter spark" but in reality, that doesn't matter much on a typical Lycoming.
Mags produce a decent spark above 2000 rpm and work just fine there, in fact, some super high power turbocharged Reno Sport Class racers still use mags.
If you're looking to pick up power WOT down low, you're not going to see much with an EI over a properly timed mag which is in good working order.
N941WR
Legacy Member
Exactly and well said!
EI's really help our engines run more efficiently as manifold pressure drops off with an increase in altitude. Because of this, our engines can put our more HP for the flight conditions with an EI that is advancing properly than with a fixed timed mag. They will not put out more HP than the engine is capable of but will run more efficiently but I think I already said that.
The other thing that helps a lot, and you don't see much written about it is that we run auto plugs that typically have much larger gaps (.032 to .035) than when running aviation plugs. This helps light very lean fuel-air mixtures and is probably why I can run well LoP with a carb.
Another tick that many EI's have is that at low RPM's and power, such as at idle, they will retard the timing (move the ignition event closer to TDC) so that the slow turning engine is not fighting against the expanding gases as the cylinders approach TDC. That is one reason many users of EI's report they can get much lower idle RPM's than when they ran mags. When the throttle is advance and MAP comes up, the EI will move the timing to the optimal timing for high power and high MAP operation without the pilot being aware of what is happening.
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FasGlas
Well Known Member
The fact is I do know what that my advance is at all times, I monitor the timing in both EI's. And if you think it's just "Spark, bang" and the gas is burnt you really need to study up on how ignitions and how fuel mixtures burn. If that were the case you'd notice no difference with one plug or two plugs firing in your planes engine. If that were the case racing engines wouldn't bother with dual plugs and extreme high energy ignitions. If burning the mixture at the exact right time didn't matter we wouldn't need accurate timing. The fact is the faster the fuel burns the more power it makes. Why do you think timing is set Before Top Dead Center? It's to start burning the mixture just before the piston hits top dead center, to get the most bang just as the piston heads back down. Low energy spark lights less mixture than a high energy spark, fact! Hence, the complete mixture takes longer to burn. Hence the piston is already heading down as the complete mixture is burnt. Next fact, a longer duration spark the more efficient the mixture is lit, the faster more complete the mixture is lit the more power is created from that charge. Low energy ignitions like mags and pmags do not burn the mixture as efficiently as high energy ignitions, fact.
And I don't care what you think, I know for a FACT that my Lancair 360 gained a good 15 knots when I removed one Bendix mag and replaced it with one ElectroAir ignition. BTW, the mags had a fresh overhaul. I tried a pair of pmags some years ago and lost a few knots (not to mention all the trouble they were), went back to ElectroAir and there were those missing knots back again. I really can't believe how little some people know about how ignitions work yet they have no problem installing them with little expectations. A good quality ignition, installed properly, WILL increase an engines horse power and overall performance.
Let's see. I built my own engine dyno (brake type) back in the late '80s and did thousands of pulls on a couple hundred engines of all types I built professionally running many different types of ignition systems from mags to inductive discharge to CDIs and multi spark CDIs. I did hundreds of pulls on another friend's engine dyno (inertial type). Never saw an appreciable hp gain from one properly functioning and timed ignition to the next outside of the experimental error in the dynos.
For the last 24 years, my company has designed and manufactured EIs for automotive and aviation- many thousands of them, many used for racing with high revving, high boost, turbo engines.
I've assisted two teams at Reno win Sport Class Gold using our equipment in 2010 and 2018.
I might, just might, know a little bit about the subject.
I never disputed that lighting off the mixture at the correct time is very important to make max hp but once it lights off, the ignition system is out of the picture for that combustion event.
As I stated before here, ignitions either light the mixture or not and a good EI with a wider plug gap increases Ignition Probability at high cylinder pressure levels and especially so when sick rich but you shouldn't be sick rich to make best power anyway, you should be around 12.5 AFR. I don't know anything about Pmag spark energy. If it's weaker than a mag, that's not good under certain conditions but an atmo Lycoming is an easy thing to light off compared to one running 3200 rpm and 85+ inches or a drag car running 9000 and 120 inches- we've done both.
The ElectroAir is nothing magical, it's a standard inductive discharge setup like SDS. Some other factor was involved with your speed increase. Either it was missing many combustion events with the mag or it was timed incorrectly- only those 2 possibilities. Lighting off EVERY power stroke at the correct time is the key to making maximum power.
You might want to brush up on ignition theory. Sounds like you have have many misconceptions based on your post above.
We don't advertise power increases from our ignition systems because based on my 35+ years experience building and testing race engines, there isn't any. You go on believing whatever you want but I wouldn't want to mislead anyone that's a good reason to buy an EI system.
15 knots on a 200+ knot Lancair or RV is a lot of power, like maybe 15%. I don't know anyone else who claims to gain 30hp on a 200hp Lyc using EI.
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Physician heal thyself.
FasGlas
Well Known Member
Well, I'll tell ya what.. I may not know what makes a woman happy or if the light goes out when I close my refrigerator door but I do know how to go fast. I don't like bloviating nor do I find it relevant but I think I can prove my point. You let me know when you get your parallel valve 360 to 300 mph, then we'll talk. I've been doing this a long time and I have nothing to promote.
rocketman1988
Well Known Member
Following
Following this discussion. A 15 knot gain would require a substantial increase in HP, no doubt.
That being said, I'm quite sure that while a 253 kt GS is impressive, that it absolutely no proof of the HP gain. With a strong tailwind, a C-172 could go that fast...
Following this discussion. A 15 knot gain would require a substantial increase in HP, no doubt.
That being said, I'm quite sure that while a 253 kt GS is impressive, that it absolutely no proof of the HP gain. With a strong tailwind, a C-172 could go that fast...
N941WR
Legacy Member
No it doesn't mean a HP gain. All it means is he finally got his timing set correctly for his engine and it is putting out it's rated HP. That coupled with an efficient airframe will easily gain you 15 knots. (He is not flying an RV.)
The same change in a 172 will gain you maybe 5 knots, maybe more, because it is a larger and dirtier airframe.
Returning to reality...
When EI is discussed, all too often folks conflate two separate subjects, (1) the methods of producing spark, and (2) the timing of that spark. Without separating the two subjects, students will not understand ignition systems...of any kind.
BTW, in reference to methods, here in the EAB world we confuse students right from the beginning by dividing the world into magneto vs electronic. In truth, "magneto" describes a method of generating electrical potential. The resulting electron flow to the coil's primary windings is controlled by a switch. "Electronic" merely tells us a solid state device was used as that switch, rather than mechanical contacts. All the other electronic feature/benefits are add-ons.
When EI is discussed, all too often folks conflate two separate subjects, (1) the methods of producing spark, and (2) the timing of that spark. Without separating the two subjects, students will not understand ignition systems...of any kind.
BTW, in reference to methods, here in the EAB world we confuse students right from the beginning by dividing the world into magneto vs electronic. In truth, "magneto" describes a method of generating electrical potential. The resulting electron flow to the coil's primary windings is controlled by a switch. "Electronic" merely tells us a solid state device was used as that switch, rather than mechanical contacts. All the other electronic feature/benefits are add-ons.
Good stuff
Been following the thread good read for us mere mortals as large as our pistons are not sure I understand how lighting off one side of the charge before the other side (one mag one EI)helps a great deal.
On another note on my right mag I installed NGK spark plugs on the slick harness 125hrs ago running them out of the box gap@ 25 and have been pleased .
Bob
Been following the thread good read for us mere mortals as large as our pistons are not sure I understand how lighting off one side of the charge before the other side (one mag one EI)helps a great deal.
On another note on my right mag I installed NGK spark plugs on the slick harness 125hrs ago running them out of the box gap@ 25 and have been pleased .
Bob
rocketman1988
Well Known Member
Or, in other words, a HP gain.
In this case, the "gain" would be from the lower HP being produced from an incorrectly timed ignition...assuming it was indeed incorrectly timed...
N941WR
Legacy Member
Bob, gain over what? If the mags were set properly for the flight conditions, then there would be no HP gain at all.
N941WR
Legacy Member
Gain over what? If the mags were set properly for the flight conditions then there would little to no gain by replacing them with an EI.
If someone has a 180 hp engine that is designed to have the optimal timing set to 25 degrees BTC but have their mags set to 18* BTC, then they are giving up a lot of power. If they set their timing to 25* BTC, the engine puts out 180 hp. That is not considered a power gain.
In talking with the OP (we used to be based at the same airport), he assumed "HP gain" meant getting more than rated power.
rocketman1988
Well Known Member
Gain
The "gain" in this case, is the difference from the reduced HP available due to the incorrect timing and the correctly timed engine (rated HP).
It is really only semantics because, as you stated, the engine was capable of the higher rated horsepower anyway.
Getting more than rated HP just due to a change in properly functioning ignition systems? Well, I would love to see some concrete data on that...
The "gain" in this case, is the difference from the reduced HP available due to the incorrect timing and the correctly timed engine (rated HP).
It is really only semantics because, as you stated, the engine was capable of the higher rated horsepower anyway.
Getting more than rated HP just due to a change in properly functioning ignition systems? Well, I would love to see some concrete data on that...
Mike S
Senior Curmudgeon
Ah yesss....
Assumed.
I, (and I suspect quite a few others) interpreted his statement as being an increase of HP over what the engine was producing at the lower airspeed.
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Are you bragging about ground speed? LOL
Well, I'll tell ya what.. I may not know what makes a woman happy or if the light goes out when I close my refrigerator door but I do know how to go fast. I don't like bloviating nor do I find it relevant but I think I can prove my point. You let me know when you get your parallel valve 360 to 300 mph, then we'll talk. I've been doing this a long time and I have nothing to promote.
I was actually asking about horsepower gained from the better spark. IN other words comparing a properly timed mag vs a properly timed EI does the hotter, longer spark actually gain any horsepower when wot at same conditions assume sea level? And if so, who's got the best spark?
Jim, if we assume identical timing, best power mixture, and good mags, I think any peak HP difference will be in the noise.
Setting timing advance aside, a crank triggered EI may deliver slightly better peak HP due to accuracy. I say "may" because personally I don't think the 2 degrees or so found in gear lash actually shows up in operation at 2700 RPM. I have been able to detect what I think is a little lash oscillation down in the low teens RPM on a 390. It's a function of torsional vibration, and will be different on a 6-cyl.
An EI arguably delivers reduced cycle-to-cycle variation, the real benefit of a wide plug gap and (typically, but not always) higher energy spark. If you dig deep into the research, the big spark shortens the tiny fraction of time between spark initiation and flame propagation to 10% burned, and tends to make that time more consistent cross a number of cycles. Beyond 10% burn there is little difference; lit is lit. If a higher percentage of cycles reach 10% at the same desired crankshaft position, there is a potential for HP increase as compared to a system which may throw in a few late burns due to non-homogeneous mixture. Note that given a quality magneto and well homogenized mixture, the only difference between the ignition schemes might be a degree or two less advance required with the EI.
The big advantage to the currently available EI's is the availability of variable advance coupled to MAP and RPM, and the ability to consistently light very rich and very lean mixtures. They also deliver the same spark energy at 100 RPM cranking speed as they do at 2700, while a mag is weaker at low RPM.
Well stated Dan.
Burn rates, peak cylinder pressure (PCP) and PCP vs. crank angle vary somewhat with each combustion event as you can see on a cylinder pressure trace. No two events are exactly the same.
Fuel injection and EI can help reduce the variability of these two parameters somewhat over a carb and mag, especially at the extreme ends of the operational AFR range, say 10 to 17 to 1.
Burn rates, peak cylinder pressure (PCP) and PCP vs. crank angle vary somewhat with each combustion event as you can see on a cylinder pressure trace. No two events are exactly the same.
Fuel injection and EI can help reduce the variability of these two parameters somewhat over a carb and mag, especially at the extreme ends of the operational AFR range, say 10 to 17 to 1.
Toobuilder
Well Known Member
The flame speed of a given mixture is governed by it's chemical composition and oxygen content. The intensity of the spark will not change the resulting flame speed. A "hot" spark will burn through oil or fuel fouling, will jump a gap under higher cylinder pressure and will ignite a very lean mixture, yes, but those are secondary considerations to flame speed. These are the edge cases where EI holds an advantage over a lower output ignition, but don't "increase" performance as used in the context of your question.
Just for fun....
Previously I said:
How about a magneto with solid state switching and programmable advance/retard, capable of lighting off 13 lbs of nitromethane fuel mix per second?
https://www.enginelabs.com/news/msd-keeping-eye-on-top-fuel-speeds-with-new-power-grid-system/
Previously I said:
How about a magneto with solid state switching and programmable advance/retard, capable of lighting off 13 lbs of nitromethane fuel mix per second?
https://www.enginelabs.com/news/msd-keeping-eye-on-top-fuel-speeds-with-new-power-grid-system/
smokyray
Well Known Member
Juicing...
Many years ago I was contemplating "improving" my garage overhauled 0-320A in my RV4. Both Slick Mags had an AD and one had a significant drop during checks. This was in the days of pre-VAF, pre internet, pre pre-drilled kits and any RV number higher than the "new" RV6.
I saw an ad in Kitplanes from Jeff Rose for his relatively new Electroair Electronic Ignition system for Experimental airplanes. Of course Klaus had his first generation LS system available at that time as well. Both systems had their merits over Mags, most of which were previously discussed on this thread.
What sold me on the Electroair was Jeff's simple explanation of his systems advantages, the best of which being, spark advance at altitude, fewer moving parts, higher millijoule spark for a longer duration across the top of the piston at the crucial time for a more efficient volumetric efficiency burn of fuel and I could use automotive spark plugs (which are much cheaper) Jeff being a Southerner helped also...SOLD! I overhauled one of my Slick Mags, removed the ailing, AD infested brother and installed a single Electroair system using Autolite 386 plugs (needing no inserts).
Performance noted? In the early 90's most RV's (including my RV4) were equipped with fixed pitch, mostly wood props. A FP prop is a fairly good measurement of HP gains as MAX RPM at a given altitude can be compared before and after a modification. Additionally, fuel efficiency at higher cruising altitudes where spark advance at reduced power can be also be easily compared. I noticed measurable improvements in all three categories, including MAX RPM at both Sea Level and at 12,500'.
Twenty Eight years, Three different Electroair systems, 3000 hours on two RV's and a HR2 later, I'm still convinced of their advantage over Mags, if nothing more than reliability. I will add that my current RV6"X" has a Electroair system and a single P-Mag which both complement each other exceptionally well.
Klaus wrote this many years ago but it does say alot for the advantages of E.I.
http://acversailles.free.fr/documen...ering/Electronic_ignition_for_aircraft_02.pdf
V/R
Smokey
Jim,
Many years ago I was contemplating "improving" my garage overhauled 0-320A in my RV4. Both Slick Mags had an AD and one had a significant drop during checks. This was in the days of pre-VAF, pre internet, pre pre-drilled kits and any RV number higher than the "new" RV6.
I saw an ad in Kitplanes from Jeff Rose for his relatively new Electroair Electronic Ignition system for Experimental airplanes. Of course Klaus had his first generation LS system available at that time as well. Both systems had their merits over Mags, most of which were previously discussed on this thread.
What sold me on the Electroair was Jeff's simple explanation of his systems advantages, the best of which being, spark advance at altitude, fewer moving parts, higher millijoule spark for a longer duration across the top of the piston at the crucial time for a more efficient volumetric efficiency burn of fuel and I could use automotive spark plugs (which are much cheaper) Jeff being a Southerner helped also...SOLD! I overhauled one of my Slick Mags, removed the ailing, AD infested brother and installed a single Electroair system using Autolite 386 plugs (needing no inserts).
Performance noted? In the early 90's most RV's (including my RV4) were equipped with fixed pitch, mostly wood props. A FP prop is a fairly good measurement of HP gains as MAX RPM at a given altitude can be compared before and after a modification. Additionally, fuel efficiency at higher cruising altitudes where spark advance at reduced power can be also be easily compared. I noticed measurable improvements in all three categories, including MAX RPM at both Sea Level and at 12,500'.
Twenty Eight years, Three different Electroair systems, 3000 hours on two RV's and a HR2 later, I'm still convinced of their advantage over Mags, if nothing more than reliability. I will add that my current RV6"X" has a Electroair system and a single P-Mag which both complement each other exceptionally well.
Klaus wrote this many years ago but it does say alot for the advantages of E.I.
http://acversailles.free.fr/documen...ering/Electronic_ignition_for_aircraft_02.pdf
V/R
Smokey
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I'll venture Klaus wouldn't write the same article today.
If one interprets "HP gain" as simply being the difference between the previous HP and the new HP, *regardless of reason*, he's correct.
Airspeed increases as the *cube root* of the increase in HP. Doesn't matter whether the lower initial HP is because of poor timing, lower mass airflow, poor air-fuel mixture, or anything else. There's no term in the equation for "timing".
N941WR
Legacy Member
If one interprets "HP gain" as simply being the difference between the previous HP and the new HP, *regardless of reason*, he's correct.
Airspeed increases as the *cube root* of the increase in HP. Doesn't matter whether the lower initial HP is because of poor timing, lower mass airflow, poor air-fuel mixture, or anything else. There's no term in the equation for "timing".
OK, let's make this easier.
If Jim has mags and they are set properly; will a properly set EI give him more HP?
The answer is: Not a measurable amount.
You guys are a rough crowd.
Concur. And given the claimed increase in speed, the previously installed mags must have been pretty poorly timed, as I calculate he would have needed around a 20% increase in HP to achieve that kind of increase in speed (all other things being equal, i.e., no change in airframe, drag, etc.).
There is no point in making up an alternate reality to sell stuff. You'll be found out soon enough and that will damage your credibility and future sales. BS is a short term marketing strategy which won't serve one well in the long term.
I noticed that as well. Good on 'em.
RV10inOz
Well Known Member
I hate to break more bad news to you, but ALL of the usable HP (usable by the prop/you) is all created on the way down. The way up is sucking power from other previous events.
Ross, Dan and a few others have covered everything else. Spending many hours on a really well instrumented dyno, really sorts the stories from facts. It might pay not understand what Ross is trying to teach you.
N941WR
Legacy Member
Ditto. The couldn't agree more.
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N941WR
Legacy Member
I have worked with people who installed their EI out of the box and the engine ran and ran smoothly. However, when properly set, their CHT's came down and speeds went up.
The Amount of the speed gain was based on the efficiency of the airframe and how far out the timing was. I did see a 20 knot gain on a Reno racer LancAir that was way out. Typical RV gains are a few to five knots with a 10 to 20 degree drop in CHT's.
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rv7charlie
Well Known Member
I wonder if the differences of opinion are the result of talking 'past' one another. I'd be skeptical of 20 kt speed gains over properly set up mags (at any altitude), but I wonder if some of the differences in perspective on power gain are the result of talking about different environments. If operating at sea level max power, neither system will have any advance, so any HP improvement would have to come from hotter and/or longer duration spark (minimal advantage).
But what about at altitude, where MAP is the limiting factor? There are usually two sides to the efficiency coin. Is there an altitude above which the mag's fixed timing can't light the fire early enough to get max pressure at the right spot in the crank's rotation? If so, is there HP to be recovered there?
Charlie
But what about at altitude, where MAP is the limiting factor? There are usually two sides to the efficiency coin. Is there an altitude above which the mag's fixed timing can't light the fire early enough to get max pressure at the right spot in the crank's rotation? If so, is there HP to be recovered there?
Charlie
This has been covered multiple times. Of course there are useful gains in hp and economy LOP and at high altitude/ low MAP. I don't think that is what the OP was asking.
These charts are lifted right from our CPI page. The one above shows how flame speed varies with AFR which is why you need variable timing to achieve best power and efficiency running leaner than best power mixture. Stoich is at about peak EGT for reference.
The chart below shows how cylinder pressure vs. crank angle varies with ignition timing. The first 60-80 degrees of crank angle somewhat past TDC is the most critical for producing maximum torque.
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Sorry, no. The amount of speed gain, *absent any other changes than to the engine*, has nothing to do with the "efficiency" of the airframe. That's FIXED, so unless you made the airframe more "efficient" (I presume you mean lower equivalent flat plate area, or some similar measurement), the speed gain, as I said, goes as the cube root of the increase in power.
For 20 knots of speed gain, assuming approximately 200 knots cruise speed for sake of argument, you'd need somewhere around a 30% increase in power. Must have been *extremely* out of timing to get that much...surprised it would run at all
Kyle Boatright
Well Known Member
Sorry, no. The amount of speed gain, *absent any other changes than to the engine*, has nothing to do with the "efficiency" of the airframe. That's FIXED, so unless you made the airframe more "efficient" (I presume you mean lower equivalent flat plate area, or some similar measurement), the speed gain, as I said, goes as the cube root of the increase in power.
For 20 knots of speed gain, assuming approximately 200 knots cruise speed for sake of argument, you'd need somewhere around a 30% increase in power. Must have been *extremely* out of timing to get that much...surprised it would run at all
You will get more speed change (in absolute mph) on a more slippery airframe than a draggy one for the same change in HP.
Imagine a 220 HP Stearman. It is a 90 knot airplane. Now, put a 450 on the nose. It is now a 113 knot airplane. The speed increase is 23 knots.
Imagine a 220 HP RV-14. Let's say it is a 180 knot airplane. Bump the HP to 450 and you'll get a 226 knot airplane. A 46 knot increase.
Um, yeah...those are both around 26% increases in airspeed, because 450/220=2.045, and the cube root of that is around 1.26.
The amount of speed gain goes as the cube root of the gain in power, all other conditions being equal.
If we take something like a Lancair 360, it would take about 19% more power to add 15 knots which would be about 34hp more. Probably closer to what the one poster was claiming.
Nobody would be using mags at Reno if they could gain this kind of hp by adding an EI. I still see lots of mags on everything from F1 to Unlimiteds.
3 main reasons for using a good EI.
1. Better starting and idle
2. Lower fuel burn and more speed/ economy up high and LOP
3. Lower maintenance costs in time and money
Nobody would be using mags at Reno if they could gain this kind of hp by adding an EI. I still see lots of mags on everything from F1 to Unlimiteds.
3 main reasons for using a good EI.
1. Better starting and idle
2. Lower fuel burn and more speed/ economy up high and LOP
3. Lower maintenance costs in time and money
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Toobuilder
Well Known Member
4. Better detonation margin at high MP
I don't think anybody would be using mags *anywhere* if you could get this kind of increase. Cessna, Piper, Mooney...everybody would have switched to EI years ago. Imagine the sales pitch...
You're suggesting the ability to program timing retard at WOT as compared to the typical aircraft magneto's fixed compromise timing?
One of many conflations of spark generation with spark timing
con·fla·tion
/kənˈflāSH(ə)n
noun
the merging of two or more sets of information, texts, ideas, etc. into one.
Well maybe not everyone. Lots of folks don't trust EIs and they are really costly to certify. I mention the Reno guys because our poster is from that community and racers are more concerned about every last easy knot and may be willing to compromise other areas to get it.
