Manifold pressure t question

[RickWoodall]

I have been searching the archives and cant find the info that I recall seeing a while back.
I have the vans MAP hose and firewall kit but am using both Dynon skyview and Lightspeed EI plasma 2 which BOTH need MAP plumbing.

Does anyone have a good link to show how others have split it and where they mounted the dynon map kit? I have heard you can restrict it...dont want to restrict it, just use a 1/4 t etc? Anyone have the skinny on best practices to do this neat and efficiently?

I am thinking of using the vans firewall pass through, and then, inside the cabin mounting the dynon manifold pressure sensor and t'ing off to feed the lightspeed box. Good idea or bad? Most seem to mount sensor on the engine side of firewall..not sure why.

Thanks.

 

[Rockyjs]

Rick,
I'm guessing that your LSE control box is mounted on a rib or backside of the sub-panel. In that case you may as well install the MAP sensor inside near the unit.
I just finished up a another aircraft not RV with a Skyview and dual Lightspeeds. I used a bulkhead fitting for the MAP hose and mounted the MAP sensor near the Lightspeed control boxes inside behind the panel. On the backside of the bulkhead fitting I adapted to vinyl hose and placed a "T" just prior to the MAP sensor to supply the LSEs with manifold pressure. If you have two LSEs the line gets split again.
As a data point without a restricter the MAP fluctuated (pulsed) in my FD180 in my RV-7 so I placed a restricter in the MAP line. I also used one in this other aircraft and the Dynon has rock steady MAP indications.

 

[RickWoodall]

Thanks

Thanks Rocky, that was what I was thinking(inside, less weather etc). I just dont really "get" the map pressure thing. I have read about the restrictor.....is that ONLY for dynon, or for lightspeed feed two? What did you use for that?

Funny, how simple and straightforward some of this stuff is and other stuff...just doesnt make sense to my little brain.

 

[N941WR]

Thanks Rocky, that was what I was thinking(inside, less weather etc). I just dont really "get" the map pressure thing. I have read about the restrictor.....is that ONLY for dynon, or for lightspeed feed two? What did you use for that?

Funny, how simple and straightforward some of this stuff is and other stuff...just doesnt make sense to my little brain.

Rick,

You will need a restrictor installed prior to the MAP sensor. The reason is that the pressure coming off of cylinder #3 rises and falls with the opening and closing of the intake valve. The restrictor smooths out those pressure waves so the Dynon (or any other EMS) can display a smooth MAP.

Here are some links for you to read through:
http://www.vansairforce.com/community/showthread.php?t=28812
http://www.vansairforce.com/community/showthread.php?t=28959

 

[elippse]

Rick,

You will need a restrictor installed prior to the MAP sensor. The reason is that the pressure coming off of cylinder #3 rises and falls with the opening and closing of the intake valve. The restrictor smooths out those pressure waves so the Dynon (or any other EMS) can display a smooth MAP.

QUOTE]

Actually, it's not just the #3 pressure fluctuating but all of the cylinders which are attached to the manifold. But you may see slightly more variation at #3 time since it is closer to the tap. The LSE has filtering after its MAP sensor, so it doesn't need a restriction. But it doesn't hurt, either!

 

[elippse]

Another consideration: What you are trying to accomplish with the restriction is to filter-out pressure variations to make the reading smoother. It is basically the same as an R-C low pass filter that uses a series resistor-the restrictor, and a capacitor-the tubing volume. The more tubing you have following the restriction the less restriction you need to use, but with less tubing, more restriction is required.

 

[breister]

I have the same setup - Dynon plus Lightspeed.

The Lightspeed tube is a lot smaller in diameter than the Dynon MAP sensor. We used a Tee before the sensor and a reducer.

We also put a restrictor (a diaphram with a pinhole in it) in the line between the tee and the engine - this prevents the MAP reading from jumping up and down. All you need is steady-state value, and the small bit of lag between throttle movement and Lightspeed timing change won't hurt anything even if you slam the throttle from stop to stop.

 

[Rockyjs]

Rick,
In addition to using a rivet that Bill used or the copper line soldered closed.

I made my restrictor by tapping the hose side of the AN fitting to 10-32 and using an old AN3 bolt screwed in about 3 threads. I then used a cutoff wheel to cut the rest of the bolt flush with the fitting and drilled a #60 .040" hole through the bolt. Make sure you clean the fitting and flush it out. I've made several of these for MAP, oil and fuel pressure indications since we don't need much flow to register the pressures.

Good Luck

 

[DakotaHawk]

Check out P/N 5670K35 on the McMaster Carr website for a Tee fitting that will work. This P/N is stainless steel, but you can buy a nylon version as well from McMaster Carr. I used the nylon Tee fitting on my RV-7.

I ran a steel braided hose with appropriate AN fittings from the #3 Cylinder to the firewall passthrough.

On the Cabin side of the firewall, I ran a couple of inches of Tygon tubing from the FW passthrough to the Tee. Then Tygon from the Tee to the Dynon MAP sensor and to the LSE brain.

(NOTE: I think the tubing sizes are 1/4" and 1/8", but measure before ordering!)

 

[Alibi]

Manifold Press T fitting

I have the same setup as u Scott. I placed an order on line with McMaster-Carr. I had to order a pack which contained 10 of the Nylon "T"'s. $10.18. I usually have all my parts shipped to Lynden W.A. This time i gave them my address in Langley .B.C. I got an email back stateing "Thank you for your order. Unfortunately, due to the ever increasing complexity of United States export regulations, McMaster-Carr will only process orders from a few long-established customers in Canada". Maggie Timmons McMaster-Carr Supply. Seems kinda proculuar that the RV builders here have most of their products shipped to their home address without a problem.