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Old 08-23-2017, 01:51 PM
JHartline JHartline is offline
Join Date: Dec 2012
Location: Carrollton, GA 5GA2
Posts: 173
Default Dual P-Mags on an IO-390


I know someone is already running this set-up, but I don't know who. Therefore this post. My MAP hose, which is braided metal, runs up to the Garmin MAP transducer. Not an option to tap into that for the MAP signal for the P-mags. So I'll be using one or more primer ports. If someone has already successfully done this I would love to peek at your notes. The points I'm pondering are:

Did you tap into one port and split the line to the left and right mags? Or would a dedicated line to each mag provide a better signal?

The manual says to use a short length of "high temp" material and transition to the 1/4" (1/8" ID) silicone tubing. What did you use for the short length and what did you use to connect it to the silicone tube?

Thanks in advance, James
James Hartline
Carrollton, GA 5GA2
RV-14 - Finish and FWF in progress
T-Bolt IO-390
Maule MX7-180
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Old 08-23-2017, 02:33 PM
TS Flightlines TS Flightlines is offline
Join Date: Apr 2010
Location: Ridgeland, SC
Posts: 1,996

James---you certainly CAN tap into your braided teflon hose, with a tee to plumb the PMags!

Tom Swearengen, TS Flightlines LLC
Teflon Hose Assemblies for Experimentals
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Old 08-23-2017, 02:55 PM
Canadian_JOY Canadian_JOY is offline
Join Date: Aug 2007
Location: Ontario, Canada
Posts: 1,606

Not specific to the IO-390, but rather a more Lycoming-generic response. I found it easier to pull MAP sensing off the #3 primer port via braided stainless conductive Teflon line, then run that line to the Vans manifold. The manifold has three ports on each of three manifold cavities. This allows for a separate line to come in from the MAP sensing on the engine, then, depending on your selection of fittings, one could install a Tee with hose barbs to run the flexible black silicone rubber hose to each of the P-mags and from the third port run another braided line to the MAP sensor. The other two manifold sections on this triple manifold provide junction points for oil pressure sensing (oil pressure sensor, oil pressure switch) and fuel pressure in our particular installation. It makes for a very neat (and safe) way to get multiple sensor connections to a single sensor port on the engine.
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Old 08-24-2017, 07:59 AM
JHartline JHartline is offline
Join Date: Dec 2012
Location: Carrollton, GA 5GA2
Posts: 173


Vans has that multi-port manifold on the top left of the firewall and they only use two of the ports - oil and fuel pressure. The map transducer mounts top right and the braided hose runs from the #3 cyl up to it. I only know the -14 so cannot comment on other installations.

I think the best place to capture a signal off the MAP hose would be 3-4" from the cylinder fitting with either one or two tees depending on what works best. Emagair is sending me a couple of tees so I'll have a better idea on a solution when I can see them.

Thanks for the insight guys!
James Hartline
Carrollton, GA 5GA2
RV-14 - Finish and FWF in progress
T-Bolt IO-390
Maule MX7-180
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Old 08-24-2017, 09:25 AM
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Raymo Raymo is offline
Join Date: Nov 2014
Location: Richmond Hill, GA (KLHW)
Posts: 1,604

I only have 1 P-Mag but plumbed and wired for two. Tom (TS Flightlines) set me up with a braided teflon hose from the #3 cyl primer port, which then goes to a double T fitting where the rubber tubes attach. One is currently plugged on my setup.
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Old 08-24-2017, 09:45 AM
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N941WR N941WR is offline
Join Date: Jan 2005
Location: SC
Posts: 11,232


Most people come off of cylinder #3, Tee off to the P-mags and the MAP sensor.

Then on the line leading the P-mags, they split it again, one for the left and one for the right P-mags.

The key to the installation is to install some type of restrictor in the line, before the first Tee so that the manifold pressure is stable.

While the MAP is a net vacuum, there are high intensity positive pressure pulses that occur when the intake valve slams shut. Some type of restrictor helps eliminate these.

PS. Check your email.
Bill R.
RV-9 (Yes, it's a dragon tail)
O-360 w/ dual P-mags
Build the plane you want, not the plane others want you to build!
SC86 - Easley, SC

Last edited by N941WR : 08-24-2017 at 09:56 AM.
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