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Pmag fuel saving?

ndotreppe

Member
Hi, I have been told that Pmag will give a 10% reduction in fuel burn compared to the standard magnetos. I need to order the engine for my RV7A and the choice is between the Lycoming IO-360 from Van's with standard magnetos and the Aerosport Power IO-375 with Pmag: will the reduction in fuel burn offset the higher price of the engine? Anybody has changed the standard magnetos to Pmag who could confirm that there is a fuel consumption reduction? Thanks, Nicolas
 
Try using the search function to find your answer.

The numbers typically reported are a one gallon (3.8L) per hour savings with one electronic ignition and a 1.5 gallon (5.7L) per hour savings with two installed.

You can ask Van's to delete the P-mags and if they say no, you can always order an IO-360 from someone else with P-mags.
 
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Maths or efficiency?

You can do the maths based on what Bill has told you and see how many hours would even up the spend.

Other tHings to think about are:

Smoother running engine
Easier starts
Lower tick over
More power

Dependent on the state of tune of each engine the 375 should give more power and will probably increase desirability and resale price.

As Bill says negotiate to buy the 360 without mags, find another supplier.... Titan supply the 360 with


As you have prob I love the PMags on my 4. I initially ran with 1 but could actually feel the extra power when I switched to two.
 
I've been down this road several times. This is my take:
- pMags are simply a superior igntion to mags. For me, I'm LOP 90% of the time and that is where the pMag advantage for engine efficiency comes in.
- Van's will sell you a new, stock Lycoming engine - you get it with mags or you don't get an engine from them.
- Everytime I crunch the numbers, getting an engine from anyone else just so it comes with pMags is a lot more expensive.

So - get the Van's airshow special with Hartzell BA prop bundled deal discount, pull the mags and replace with pMags, then sell the mags to those who still like flying behind them. This is a sure fire approach to getting the best deal out there.

Carl
Keeping an eye on Sun N Fun for the Van's show special announcement - the new RV-8 project needs an engine!
 
Its not the Pmags that give you a better fuel burn- its ANY electronic ignition with an advance curve that will give you better fuel burn. And there are a bunch of them out there now. That said, you need to evaluate how you fly. The higher and leaner you fly, the bigger the benefit. If your typical mission is down low and full rich, then there will be little fuel savings regardless of ignition choice.

I have dual Pmags on one airplane, and also had dual Pmags on a prior and as Bill said above, my fuel burn reduction was right on the money. They have been great to me, but if I had to do it over, I'd go CPI. Much more adjustable, and much less money.
 
Pmags

I've been down this road several times. This is my take:
- pMags are simply a superior igntion to mags. For me, I'm LOP 90% of the time and that is where the pMag advantage for engine efficiency comes in.
- Van's will sell you a new, stock Lycoming engine - you get it with mags or you don't get an engine from them.
- Everytime I crunch the numbers, getting an engine from anyone else just so it comes with pMags is a lot more expensive.

So - get the Van's airshow special with Hartzell BA prop bundled deal discount, pull the mags and replace with pMags, then sell the mags to those who still like flying behind them. This is a sure fire approach to getting the best deal out there.

Carl
Keeping an eye on Sun N Fun for the Van's show special announcement - the new RV-8 project needs an engine!

If you go this route, mags will sell for more if new. The downside is it most likely will invalidate the warranty. I asked Lycomming and got a really vague answer.
 
Hi, thanks for all your answers. My preference goes to the Aerosport Power however I have already the cowl (without scoop) and the firewall forward kit (for the Lycoming) is on the boat to France.
Has anybody installed the Aerosport Power and use the standard van's cowl and exhaust? Any feedback on installation problem? It seems that they are identical in size so there should be no problem to adapt?
Thanks, Nicolas
 
I have the IO-375 in my RV-7. I think the fuse is the same or very similar. I have the standard Vans cowl without the scoop, so forward induction with a Superior cold air sump. Can?t comment on the exhaust as I got one from Vetterman which fits nicely.
The IO-375 has the exact same dimensions as the IO-360, so no modification required.
 
Hi, I have been told that Pmag will give a 10% reduction in fuel burn compared to the standard magnetos. I need to order the engine for my RV7A and the choice is between the Lycoming IO-360 from Van's with standard magnetos and the Aerosport Power IO-375 with Pmag: will the reduction in fuel burn offset the higher price of the engine? Anybody has changed the standard magnetos to Pmag who could confirm that there is a fuel consumption reduction? Thanks, Nicolas

I never had standard mags on this airplane. I routinely get 155-160KTAS cruise at 7.0 - 7.7gph once leaned out at 9500'-12500'. EFIS usually showing 60-65% power.

0-360 with Precision fuel injection with dual P-mags.

Bevan
 
Nicolas,

If you go with P-mags (or any other electronic ignition), make sure they are configured properly for your IO-375.

The P-mag default timing with either the jumper in (A curve) or out (B curve) may not be correct for your engine.

You can always tune them to your engine manufacture's recommended timing with a PC using the EICAD program available free from the Emag website or with the EICommander.

Feel free to contact me off list with any questions regarding the configuration. (I'm one of the two guys behind the EICommander and will be more than happy to answer any of your questions, regardless if you have an EICommander or not.)
 
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I have the IO-375 with dual P-MAGs. I run LOP everywhere. My fuel flow is 7.5 gph up to about 11,000 MSL. Above that, I am around 6.5 gph.

I'm approaching 5 years and 700 hours on my RV-8. If you figure I've saved one gallon per hour at $4.50 per gallon of avgas, then I have saved $3,150 in 5 years. This engine will probably go 20 years before overhaul, and the cumulative fuel savings during this period will make me feel better about the large overhaul expense someday.

Of course, the reality is that I spend my fuel savings on more fuel to go flying even more. But it's fun trying to convince myself that aviation is somehow more economical! :)
 
maybe...

There is some additional efficiency that can be exchanged for lower fuel flow... mostly through smooth running lean of peak. For me, I look at mpg as the most relevant metric and shoot for the fastest speed that I can get at a reasonably efficient mpg. Could be anywhere from 8 to 12 gph in cruise. I use less in formation and can dial back to lower flows but they generally don't result in a significant improvement in mpg until the airspeed falls below 150 mph.
 
I believe electronic ignition allows for smoother running Lycoming engines at lean of peak mixture settings, allows smoother running at low rpm and maybe easier starting. But the CAFE reports seem to indicate higher horspower with magnetos. My experience is I can get excellant mileage with magnetos running rich of peak. I have a screen shot from 2014 of my RV8 powered by a Superior IO360 getting 5.85 gph rich of peak at 11,859 feet density altitude at 158 ktas.

11sdlyu.jpg
 
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I like Christo's approach, looking at the overall nm/gal. I should do that too. I have a nm/gal readout on my Dynon Skyview. I'm usually around 21 nm/gal when lean of peak, 7.5 gph and 170 ktas. I've had it up around 25 nm/gal with good tailwinds.
 
The dirty little secret of electronic ignitions is they don't really improve "power".

If you have mags and stay in the pattern doing touch and goes for two hours and then switch to EI and do the exact same flight again, your fuel burn will be very close to identical. The reason is the EI should set the timing close to, if not exactly, the same as the mag.

At altitude is where the EI shines because they let the timing advance and since we typically run auto plugs with a much larger gap (which gives a bigger spark) allows for more aggressive leaning. The advance allows for more efficient combustion at altitude, which we see as reduced fuel consumption at a given speed or higher speed at a given fuel consumption; your choice.

If an EI and a mag are set for the same timing, I'm not sure you could measure the difference.

All that ssid, I will take my P-mags over a mag any day!
 
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I recommend reading the CAFE Foundation studies on electronic ignition published in three articles titled "Ignition Dynamics I, II and III" for a scientific comparison of electronic and magneto ignition in aircraft.
 
I began flying my 9A with mags. Don't recall exactly how long it was before I switched to a P-Mag on the right, maybe about 75 hours. (Don't have the logbook here in front of me.) That swap saved me an even gallon per hour, and made for easier starting. No noticeable increase in speed. About 50 hours later, I added the second P-mag. I didn't get much fuel savings from that, about .2 gph, but I was able to idle down to get more braking on landing, and gained 3-4 knots at 8000' The engine is a bit smoother also. It is a 160 hp O-320 with a three blade Catto that Craig set up for P-Mags from the start. I can't give numbers on climb, but it did improve when I put on the second one. Didn't have good numbers about climb with two Slicks. BTW, I have set the idle as low as 400 rpm, and it is very smooth on final, with almost as much braking as CS. I don't pull it all the way back on the ground as it needs a little more there to be smooth.

Bob
 
Hi All,

I'm just finalizing my engine settings for my POH and had a question regarding the fuel flow settings for given engine powers. My engine is an IO-360M1B (8.5:1 CR) modified only with dual PMAGS and and EI-Commander. For a power setting of 22"MP and 2200RPM according to Lycoming power charts (mixture set for best economy) I should be seeing a fuel flow of 49lb/hr, or 7.9GPH. This is assuming a stock standard engine. If I add PMAGS to this equation should I really be expecting a 1GPH saving, for exactly the same power output and subsequent airspeed?
The reason ask is that I'm trying to work out were to set the target EGT's, because how many degrees lean of peak you should be at will be dependant upon power setting, and if I'm off by 1GPH (6lb/hr), this would take the engine output according to the Lycoming fuel consumption chart to almost exactly 75% power, where according the David Brown and the APS crowd I should be operating at 40degF lean of peak, rather than at peak as you would at 65% power.
Quite humbling displaying your fundamental ICE misunderstandings for the world to see, but I need to get my head around this as I really don't want to be screwing things up.
Cheers,
Tom.
2zxw9vm.jpg
 
Tom,

LOP at that 22? and 2200 RPM with pMags I?d expect fuel flow at around 7GPH or perhaps a little less. In the 8A standard 170kt+ LOP cruise is 23.5-24? and 2350-2400 RPM @ 7.5 - 7.8 gph (altitude dependent)

On target EGTs, I offer trying to figure that out with a sharp pencil may be an interesting exercise, but of little practical value. Once flying you will know fuel flow to get the desired LOP conditions for the altitude and power setting (I find 20-30 degrees works well for me at all cruise settings).

Carl
 
I'm with Carl here. The charts are an OK starting point, but in reality you are going to have to see what your particular configuration likes. There is no magic EGT target nor a universal advance figure. Some days you may find peak EGT is best (to push through a headwind, for example), while other times you might pull it back to 50-60 LOP to really stretch the endurance. And BTW, the "optimum" advance setting will be different between those two EGT readings too, despite the fact that you might have identical MP and RPM settings. That's why it helps to have the ability to adjust advance in the cockpit.
 
FWF fit

Hi, thanks for all your answers. My preference goes to the Aerosport Power however I have already the cowl (without scoop) and the firewall forward kit (for the Lycoming) is on the boat to France.
Has anybody installed the Aerosport Power and use the standard van's cowl and exhaust? Any feedback on installation problem? It seems that they are identical in size so there should be no problem to adapt?
Thanks, Nicolas

Nicolas,

The engine will fit the stock Vans cowl just fine. Since you mentioned you already ordered the FWF kit and asked about fit, there may be some potential issues with some of the bits in that kit fitting the Aerosport engine depending on your install.

If you end up with a Superior Air Parts Horizontal induction sump, the throttle and mixture cable brackets will not fit. I also had to order the next size up for the throttle cable for it to fit with the custom bracket I made. Also check the length of the fuel and oil lines supplied with the kit. Again, depending on how close you stay to the 'stock' Vans plans, one or more may not fit. I was able to use all but one fuel hose due to the FWF mounted fuel flow sender. Finally, if you have not already, confirm with Vetterman that the exhaust in the FWF kit will fit the engine. I had to order mine directly from Vetterman due to the engine choice I made with the nose gear plane.
 
Thanks guys. After my break in period is over, I think I'll shoot for around 7 to 7.5gph for my first LOP operation to guarantee I'm out of the high power danger zone and then see how things go from there.
I just hope I hit the Van's performance numbers, else I'll be bitterly disappointed.
Cheers,
Tom.
 
Thanks guys. After my break in period is over, I think I'll shoot for around 7 to 7.5gph for my first LOP operation to guarantee I'm out of the high power danger zone and then see how things go from there.
I just hope I hit the Van's performance numbers, else I'll be bitterly disappointed.
Cheers,
Tom.

As has been said many times: "There is no such thing as a free lunch."

With more than 20-years and 3,300+ hours of RV flying, you cannot get the speed without the horsepower AND to get the horsepower, you need to feed the horses fuel. In other words, reducing fuel burn will reduce horsepower and the reduced horsepower will reduce the speed.
 
As has been said many times: "There is no such thing as a free lunch."

With more than 20-years and 3,300+ hours of RV flying, you cannot get the speed without the horsepower AND to get the horsepower, you need to feed the horses fuel. In other words, reducing fuel burn will reduce horsepower and the reduced horsepower will reduce the speed.

That's assuming all things are equal. And in the case of a magneto with fixed timing compared to an EI with an advance, they are NOT equal. It is very easy to get the same speed at a lower fuel burn and/or more speed with the same fuel burn with an EI. This is particularily true the leaner and higher you go. I have demonstrated this many times (every cross country, in fact) with the LOP advance feature of my SDS ignition. When I go LOP and get the 9 knot sag in TAS, the flip of a switch which activates the additional advance gives me back almost half of the loss... With no change in MAP, RPM or FF. And its noteworthy that this 3-4 knot spike is in addition to the substantial speed increase I see over the same airplane with magnetos.

No, there is no free lunch, but the fact remains that the default standard in aviation engines (magnetos) are so bad at high altitude, lean flight that there is ample opportunity for improvement.
 
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Thanks guys. After my break in period is over, I think I'll shoot for around 7 to 7.5gph for my first LOP operation to guarantee I'm out of the high power danger zone and then see how things go from there.
I just hope I hit the Van's performance numbers, else I'll be bitterly disappointed.
Cheers,
Tom.

Fuel flow is a result, not a indicator. Use peak EGT as your key reference point. Initially ballpark 150F~175F ROP for climb, 100F~125F ROP for best power cruise, and as far LOP as you like for economy cruise. "Like" is mostly a matter of acceptable speed loss. At altitude (meaning lower available MP) you can put mixture almost anywhere.

Later, you'll know what fuel flow to expect at your typical power settings and altitudes. Record those in your POH, if you feel the need.

You mention the "high power danger zone". I suspect you're speaking of the popular red box or red fin or whatever. It's not bad as a concept, but the given numbers appear to be ultra conservative for a NA Lycoming. With fixed timing, worst case (pro-detonation) temperatures, and ham-handed management (like 28.5 MP and 2400 RPM), the detonation range is roughly 100F ROP to 60F LOP. That range is painless at lower MP, i.e. with enough altitude. I suspect variable timing does not extend the range, as timing doesn't advance unless MP drops. I don't know of any published data on that score.

I suggest reviewing the "target EGT" method for climb.

Most will not make Vans book numbers while running LOP.
 
Thanks Dan. Yes, you are correct in that I was talking about the red box.
I guess I'd just been looking for a way of setting the engine up without having to rely on finding the peak EGT, hence the reliance on the fuel flow. I guess I've had a bit of an aversion to finding the peak EGT as I'm always concerned about doing damage to the engine whilst finding this peak, thus in the past for aircraft without engine monitoring, I've always done a big mixture pull, then richened enough to run smooth. How long do I really have to find this peak EGT, and in this regard, are the CHT's are substantially slower to follow (and subsequent risk of any issues) because of the increased thermal mass in the cylinder/piston assembly v's the air alone in the cylinder? Until now I've never flown an aircraft before with full CHT/EGT monitoring, so I'm a little naive on these things, but this G3X setup I'm just finalizing will have the full monty from a monitoring perspective.
Tom.
 
Tom,

While there is a natural hesitation to explore the edges of limits (peak), the fact is in this case, most of us have done it many times without even knowing it. The long held standard of "...lean to rough, then enrichen to smooth..." we were taught from the early days of training actually goes right past peak (rough), and more often than not, the "smooth" is actually peak or very close to it, depending on the health of the magnetos.

The BMP, followed by enrichment to peak is generally a very safe method. Also, CHT's will be reduced from best power with a leaner mixture, though as you suspect, they will react much slower than EGT to mixture changes.
 
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Thanks Michael. Sounds like I need to stop thinking about it and just get in and have a crack at it.

Tom.
 
Dual P-mag real world fuel usage (IO-320)

I keep a spreadsheet for all of my fuel expenses that tracks everything.

Last year I flew 149 hours and averaged 6 gallons per hour at a cost of $26 per hour for gas. This is mostly cruising at altitudes around 7-10,000' going 147-150 Knots True airspeed. The previous year was basically the same. Flew 141 hours, averaged 6 gph, fuel costs were slightly lower at $25.50 per hour. Same cruising speeds/altitudes.

I always fly Lean of Peak unless I'm taking off.
 
I guess I've had a bit of an aversion to finding the peak EGT as I'm always concerned about doing damage to the engine whilst finding this peak, thus in the past for aircraft without engine monitoring, I've always done a big mixture pull, then richened enough to run smooth. How long do I really have to find this peak EGT, and in this regard, are the CHT's are substantially slower to follow (and subsequent risk of any issues) because of the increased thermal mass in the cylinder/piston assembly

As Mike said, you've been finding peak your whole flying career, and haven't hurt one yet.

Lycoming recommends cruising (<65%) at peak EGT for maximum economy (SI-1094D). I routinely run my 390 at peak with fixed 23 degree timing, as it offers a good balance of speed vs economy, about 9 GPH at ~183 KTAS. Or I can burn less and go slower, or more and go faster. Or I can advance the ignition timing and pick up some speed at the same fuel burn, with higher CHT. There is no "one way" to do it.

As for high power, like climb, take a look at the "Maximum Manifold Pressure for Continuous Operation" line on the lower left side of your standard Lyc power chart. Stay to the left of that line with mixture at best power, 100~150 F ROP range. As a rough rule of thumb, the line is 4" oversquare, so even with advanced timing (the p-mag), it would be hard to get in trouble if you give yourself a very conservative rule and maintain square operation.
 
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