Where to hook up PMag MAP tube?

Craig23 · #1 03-27-2009, 10:31 AM

Where have other PMag users hooked up the manifold pressure tube and what fittings did you use? I have the standard Van's manifold pressure line coming off the port at the back of the #3 cylinder. I thought about using a T fitting in the port, but would then need to run some sort of high temp material between the fitting and the PMag tube.

What have you guys done?

scard · #2 03-27-2009, 10:37 AM

Not that I'm a Pmag user anymore, but here is how I did it when I was living on the edge:
http://rv9a.card-net.org/archives/20...sure-fittings/

Steve Sampson · #3 03-27-2009, 01:54 PM

Craig, I took the pressure from the engine manifold to one of those manifold blocks that VANS supplies for all the transducers, using the parts VANS supplies in the MP sensor kit which include a restrictor to ensure the engine does not go excessively lean if an air leak developed downstream.

The VANS manifold block then has two empty holes that connect to the manifold line. I used two simple nylon fittings which screw in , one for the tube that goes to my AFS manifold pressure sensor, the other to a tube connecting to the P-mags. That has a T-piece in it so it connects to both.

Not the most robust fittings, but what is the downside of a leak. The P-mags would retard a little, the MP reading on the gauge would be wrong and the engine would go minutely lean.

I hope my explanation is clear. I unfortunately don't have a good picture.

penguin · #4 03-27-2009, 04:19 PM

Craig,

I'm not familiar with the Van's set up, but I have used the #3 primer port with an AN816-2D fitting installed (1/8 NPT and 1/8 37 deg flare). I then used 1/8" primer line to an 1/8" T (AN824-2D) P-clipped to the baffling. The MP hose supplied by emag fits very well on 1/8" primer line. The other end of the T can go to an MP sender, the other P-mag, or be blanked off for future expansion. I'll try to post a picture in the next few days.

Pete

N941WR · #5 03-27-2009, 07:05 PM

I used a bulkhead fitting to bring the MP line through the firewall, then rubber tube to go from there to the MP sensor.

In this picture you can see the black vacuum line come back out through the firewall and supported with adel clamps as it goes across the top of the engine mount.

All the Tee fittings came from the Aviation Drip Irrigation isle at my local big box hardware store.

Craig23 · #6 03-27-2009, 09:21 PM

I like the idea of the aviation drip irrigation aisle. I think I even have some of those parts laying around. I also like Scott's photos. A few of you have mentioned restrictors. I don't remember anything about restrictor fittings in the plans. Do I need to add that?

RV7Guy · #7 03-27-2009, 10:18 PM

I used a Stainless Steel T fitting from Petsmart, $1.79. Check the aquarium area.

Quote:

Originally Posted by N941WR

I used a bulkhead fitting to bring the MP line through the firewall, then rubber tube to go from there to the MP sensor.

In this picture you can see the black vacuum line come back out through the firewall and supported with adel clamps as it goes across the top of the engine mount.

All the Tee fittings came from the Aviation Drip Irrigation isle at my local big box hardware store.

OneCharlieKilo · #8 03-28-2009, 01:24 AM

Here's a picture showing how I did mine (worked fine for 26 hours with dual p-mag setup and last 4 hours or so with Slick mag / p-mag setup). The three port aluminum block has hose from #3 cylinder coming into the block from left side of picture (right side of firewall if looking forward) with pipe thread to barbed hose fitting coming out top going to the p-mag(s) and same type fitting/tubing coming out right side of block in picture (left side of firewall if looking forward) going to manifold pressure sense fitting on engine monitor. The tubing from top of 3-port block in this photo shows tubing going to a T-fitting to feed both p-mags when I was running dual p-mags; has since been modified to eliminate the T-fitting since only feeding to one p-mag now. I think the tubing came with either the p-mags or my engine monitor and I got tubing fittings from hardware store and pet store aquarium section. The 3-port block I ordered from Aircraft Spruce (you can custom order for number of ports you want and fitting size desired):

Side note: this picture was taken prior to first flight and yes, I did seal and protect those FW penetrations later.

http://rv6aproject.ckhand.com/panelA...Pg3.htm#photo6

Steve Sampson · #9 03-28-2009, 02:21 AM

Quote:

Originally Posted by Craig23

I don't remember anything about restrictor fittings in the plans. Do I need to add that?

Craig, without a restrictor, if the line to the primer port became 'open' the mixture would go weak. I have no idea how weak, but I do know that VANS supply a restrictor in their MP kit, so it makes sense to put one in the system to my mind. It can do no harm since if everything is working properly there is no flow in the system, just a fluctuating pressure.

N941WR · #10 03-28-2009, 07:30 AM

Quote:

Originally Posted by Craig23

... I don't remember anything about restrictor fittings in the plans. Do I need to add that?

Craig,

I flew w/o a restrictor and found it is needed. Othewise your MP will bounc all over the place, causing the timing in the P-mags to bounce as well. I drilled a VERY small hole in a an AN470-4 rivet and put it in the bulkhead fitting as the line passed through the firewall.