Manifold Pressure to the P Mag

How are people connecting to the IO 390? I would like to use the port on the #4 intake port but don't know where to order or what part number. I have 2 P Mags installed. Do both need the MAP connected?

Yes, both P-Mags require manifold pressure, which it typically off the #3 cylinder (on a 4 cylinder engine).

Tom at TSFlightLines (aka Hoser) can set you up with what you need.

Make sure to include some type of restrictor to smooth out the power pulses. Otherwise the timing will bounce around.

You can see this happen on our EICommander, so it is not just theory.

N941WR said:

Make sure to include some type of restrictor to smooth out the power pulses. Otherwise the timing will bounce around.

You can see this happen on our EICommander, so it is not just theory.

Click to expand...

Somewhat related question - I have both pmags looking at MAP from the 1/8" copper line that used to be the #4 primer. Is that enough restriction or should I put something else in place?

Or, more broadly, what size restrictor would you recommend?

CamTom12 said:

Somewhat related question - I have both pmags looking at MAP from the 1/8" copper line that used to be the #4 primer. Is that enough restriction or should I put something else in place?

Or, more broadly, what size restrictor would you recommend?

Click to expand...

My restrictor hole size is the second smallest drill size in my box of numbered drill bits. (I broke the smallest.,)

I center drilled a short AN470-4 rivet and stuck it in the fitting on my #3 cylinder and then attached my vacuum line. The rivet can't move into the cylinder or down the hose.

When we were developing the first gen EICommander, which had a manifold pressure display, we could see the MAP bouncing around AND the timing on the two P-mags differ, which caused Timing Divergence Alarms on the EIC. Putting in that drilled rivet solved both issues.

Via our customers, we discovered that some EFIS displays smooth the MAP pulses with software and some do not. So there are undamped P-mags (and other EI's) out there that are firing at different angles from each other.

Send me your email address and I will forward you our Q&A document, which will answer a lot of your P-mag questions.