Manifold pressure sensor + E/P-mags

[Davepar]

As a big disclaimer, I haven't flown with this yet. It looks like it will work good, though.

I was in a quandry as to how to connect up everything that needs manifold pressure (MAP). There's a 1/8" pipe thread hole on the back of cylinder 3 that needs to connect to a MAP sensor (mine is from AFS) with a 1/4" tube fitting and two P-mags with 1/8" tube fittings. The P-mag can be run without MAP, but it won't alter the timing as aggressively and thus won't be as efficient.

The prior tried-and-true method of connection is the IE VMP install kit from Vans for $55. It uses a flexible hose from the cylinder to a firewall fitting and the sensor is thus aft of the firewall. That would be OK, except the P-mags are forward of the firewall. Either the hose needs to be cut or some other fitting attached forward of the firewall. I also had a preference for installing the sensor forward of the firewall and thus only a wire would need to go through the firewall.

Parts:
AN840-4D nipple, 1/8" pipe thread to 1/4" hose (Aircraft Spruce and others)
High-Temp Silicone Rubber Tubing, 1/4" Id, 1/2" Od, 1/8" Wall, Black (McMaster Carr part# 5236K882, $1.83/ft)
Polycarbonate Single-Barbed Tube Fitting Reducing Tee for 1/4" X 1/8" X 1/4" Tube Id (McMaster Carr part# 5117K33, $7.97 for pack of 10)
Polycarbonate Single-Barbed Tube Fitting Tee for 1/8" Tube Id (McMaster Carr part# 5117K13, $5.52 for pack of 10)

The P-mags included some 1/8" high-temp silicone rubber tube, but McMaster sells that as well if you need it. The T's come in packs of 10. If anybody near Seattle needs them, I have 9 spare sets available for one beer each.

I mounted the sensor on the front of the firewall. It's designed to be in a car engine compartment, so I see no problem with it being fw-fwd. The AN840 fitting goes in the cylinder. The 1/4" tubing goes from the AN840 to the MAP sensor via the 1/4" to 1/8" reducing T. The 1/8" tubing and T then connect to the two P-mags. The hose is very secure on the T's and P-mags. On the sensor, I might use a small hose clamp. Spruce sells a "Herbie" clamp that looks good for this. The P-mags came with some similar plastic clamps that I used on the P-mag fittings, although I doubt they are needed there.

The one remaining piece of the puzzle is flow restriction. The AN840 needs to be altered to limit the air flow. The sensors should even out the readings, but it's also a safety measure in case a hose fails. I decided to epoxy an AN426AD5-4 rivet into the engine side of the fitting with a 1/16" hole drilled in it. Another option might be to fill the non-engine side of the AN840 with JB-Weld or weld it shut and drill through that.

Dave

[frankh]

supplied in my Vans firwall FWd kit. one for MP and the other for Oil pressure.

You could also make one by visiting your local hydraulics shoppe...They have all the fittings there in steel. You could then braze the end closed and drill a hole, just like your JB weld except with real weld...You could use silver solder as well and a good blow torch.

AS an aside the 45deg fitting is a bear to take ou if you ever have to with the engine mount in the way. A straight fitting can be taken out and reinstalled with a deep socket, once again the fitting can be ourchased in steel from your local hydraulic emporium.

Frank

[MCA]

Except I used the standard Van's MP hose and ran it to the firewall. The MP sensor and Tee is inside. I then ran the single flex tubing, along with some wires, back out to the P-Mags.

Just another way to do the same thing... both ought to work fine.

[apkp777]

Need to revive this old thread. Does anyone have any updates on MAP sensor - to intake - to dual P-mag hose connections.

[N941WR]

Tony,

I've been running similar setup with no problems. However, you MUST put some type of dampener in the system, before the Tee fitting. You don't want your P-mags getting a MP reading that is jumping around.

In my installation, the MP sensor is aft of the firewall. An AN807-4D was used. Once inside the firewall, the Tee was added and the P-mag line was routed out the firewall. Once in the engine compartment small Adel clamps were used to route the line along the top of the engine mount to the P-mags.

To smooth the pressure readings I drilled a very small hole in a AN470-4 rivet, the length doesn't matter, and put it in the AN807 fitting. The head is just large enough so it won't move around and the small hole smoothes the power pulses.

Just one way to solve this problem, there are many others.

[apkp777]

Originally Posted by N941WR

Tony,

I've been running similar setup with no problems. However, you MUST put some type of dampener in the system, before the Tee fitting. You don't want your P-mags getting a MP reading that is jumping around.

In my installation, the MP sensor is aft of the firewall. An AN807-4D was used. Once inside the firewall, the Tee was added and the P-mag line was routed out the firewall. Once in the engine compartment small Adel clamps were used to route the line along the top of the engine mount to the P-mags.

To smooth the pressure readings I drilled a very small hole in a AN470-4 rivet, the length doesn't matter, and put it in the AN807 fitting. The head is just large enough so it won't move around and the small hole smoothes the power pulses.

Just one way to solve this problem, there are many others.

Thanks Bill,

That helps. Take a look at my Vetterman installation post and see if you can give me some input on that. I am not sure how much clearance I need for the tail pipes. http://www.vansairforce.com/communit...ad.php?t=57187