As i was searching the internet for various rotary things i found an adapter to get your MAP pressure signal from the housing instead of the intake tract. I'm curious if this would help in ITB or P-Port situations where using MAP instead of TPS to tune is much more difficult. Thoughts?

 

There are two issues that plague the MAP reading. The first is overlap, where the sensor is exposed to the positive exhaust charge. The second is the volume of air where the reading is taken and overall smoothness of the air being sucked out of that chamber beneath the throttle body. This solution will do a much better job with the first issue, but may not accomplish enough with the second issue to make the signal steady enough for smooth idle and cruising under light load. If you have a PP or large BP, it's certainly worth trying. But for ITBs on a typical street port I think you won't see much difference between the reading from the manifold.

 

Also wouldn't this air charge include some fuel tool? which would skew readings/damage sensor.

 

I'm sure it would be a bit more fuel exposure than having an intake based vacuum source. I wonder how problematic it would be. The FD has a little filter on the vac line that runs to the MAP sensor, maybe that would prevent any issue with the fuel.


I found this on rotaryeng.net which is mostly an aviation focus on the Mazda rotary. They have a couple "nifty" little parts, and a bunch of info on the website.

 

No problem, as long as the MAP sensor is elevated above the motor so that any fuel vapor will run back down the tube when it condenses. Anyone that places their vacuum lines below the injectors has the same issue, which is pretty much anyone running a Weber-style EFI system.

 

in the FC the MAP line is below the secondaries and the map sensor is about parallel in car height with this but that does not experience this issue?

 

I don't have a vehicle in front of me to verify that, but from the diagram, it looks to be connected to a single primary port on the upper manifold (meaning above the primary injector) and as stated above has a little filter on it. It won't see air with fuel mixed in it (not regularly at least) and air won't be pulsing through any portion of the line.





Using the filter that came with the FC should relieve you of any concern, but as I stated earlier, any vacuum hose leading up to that filter should have an upward trajectory, otherwise condensing fuel could end up collecting in it. I saw it happen on my REPU after only a few hundred miles of driving. The clear hose I was using had a dip in it and it was filled with fuel. Truck still ran, and there was plenty of additional hose between that dip and the MAP sensor, but once I removed the dip in the hose I never saw fuel in the line again. I need to get one of those filters...i just haven't gotten around to it.

 

Aside from the issue/non-issue of the fuel vapors. Does anyone know if the vacuum signal from that location would work well for speed density based tuning. I feel like it should give you some vacuum signal, but maybe not as strong of change between loads as the pre intake port signal. I'm honestly just guessing. I kind of want to put on in my rx8 and see what kind of signal i get from it when hooked to an analog vacuum gauge.

Matt