Pmag conversion numbers

[Kokemiller]

I am considering converting a mag to a Pmag. I've seen a lot of posts indicating a decreased fuel flow of .5 to 1.0 gph by doing so. That would indicate to me that throttle is being pulled some due to more power being made. If that is the case I would assume that static and or WOT rpm would also increase. I haven't been able to find this info in the archives so if anyone has some real world mag to EI performance number I would appreciate.

[Bavafa]

I would very much be interested in the same info as well from the users who have switched from mag to Pmag as I am considering changing one mag as well. It is just that my engine is running well and worried of 'why fix some thing when is not broken' thing.

[humptybump]

I'm hoping some first-hand feedback. All I have is what I've read...

... I had read that th fuel burn at sea level is about the same as a regular MAG. The difference being the P-MAG has a longer duration spark to maximize fuel burn. Things start to change with altitude. A MAG has a fixed spark advance of 20 degrees before top dead center (BTDC). However, the P-MAG has a spark advance profile (actually two of them) and can time the spark more efficiently as engine RPM and manifold pressure change (typical with altitude increases).

Here is a good reference to the timing profiles elsewhere in the forums ...
http://www.vansairforce.com/communit...ad.php?t=62158

[N459RC]

My o320e2d increased about 30 rpm static. About 4 mph increase in speed.

[SebsRV7A]

My two cents...
I've always had dual PMags on my RV-7A. I went up with a friend of mine several months ago. His airplane is basically the same, with the same engine but dual mags. We were working on running lean of peak. He was initially leaning too quickly and wasn't able to get lean before it got rough. I had him lean MUCH slower. He was able to get just lean at a low power setting without getting rough. On my engine, I can lean it until all cylinders quit working at the same time (at 150-200 LOP). You won't want to run that lean because you lose too much speed, but the combination of spark advance and much higher voltage of EI allow the plugs to fire with a leaner mixture. This gives reduced fuel burn. LOP ops give up a small amount of speed for a large decrease in fuel burn. I don't have fuel flow, but I give up about 10 knots for 3 gal/hour (based on lots of 2 hour flights and a fillup after landing).
I'm sold on the combo of electronic ignition and LOP operations.
I have a CS prop, so no RPM change...
Hope that helps.

Seb Trost
RV-7A
Boulder City, NV

[Kokemiller]

Thanks for the replies. Just had Catto repitch and add Nickel leading edge and now can only turn 2010 RPM static. Before I repitch again I wanted to find out how much EI might change things.

[N941WR]

Originally Posted by Kokemiller

Thanks for the replies. Just had Catto repitch and add Nickel leading edge and now can only turn 2010 RPM static. Before I repitch again I wanted to find out how much EI might change things.

You won't notice much difference on a static run on the ground. The P-mags are designed to recognize full power (High MAP and RPM) and set the timing at the bottom of the scale, close to a standard mag. It is up high, in cruise, where they make a real difference. (High RPM and low MAP)

That said, you might notice a difference on the ground due to the better spark. Not to mention the plane will be easier to start.

[Toobuilder]

The -8 used to have dual Bendix mags and trying to go LOP would produce noticable roughness at only 30 LOP, and the fire out almost completely (engine quits) at 50. With the dual Pmags, I can get all the way to 100 LOP without any stumble at all. That's incredible! And that is where the fuel savings comes into play- it's the ability to make the same power on a leaner mixture than without. If you run everywher at full rich, you're not going to realize any GPH change (but you might be faster).