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Old 02-19-2006, 08:19 PM
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MAP sensor location?

Where is the best place to locate the MAP sensor in a tunnel ram intake?
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Old 02-19-2006, 09:29 PM
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Off the top of my head I would think in the interest of achieving a solid map signal I would tap a hose barb into each plenum under the throttle body and Y the two hoses into one then into the map sensor. I'd locate each hose barb right under the throttle bodies.
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Old 02-19-2006, 10:15 PM
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you want the MAP to draw vaccum from the intake manifold. So, anywhere in the intake should be sufficient....
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Old 02-20-2006, 09:13 PM
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Confused

Now I am really confused. I called the Holley (Weiand) tech line today and the 'tech' says it dosen't matter where I put it as long as it is below the throttle blades. Then I searched their website and found this diagram. Surely someone has studied the air flow in a tunnel ram.
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Old 02-20-2006, 09:36 PM
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Nothing to be confused about, see if this helps. What you are trying to do is connect the map sensor to see manifold absolute pressure, or what we normally call vacuum. To sense this the sensor bung must be located below the throttle blades. It also must/should/ highly suggested be located within the plenum so it reads all the pressure drops from all the cylinders. This gives a smooth signal and is why you don't want the sensor bung in a runner.

That diagram is for a throttle body that has multiple predrilled ports under the throttle blades to pick up the manifold pressure signal. It appears you have a manifold port in the lower center of each throttle body. When you remove the plug if that port goes all the way through the throttle body and opens under the throttle blades that's a port that you can tie in the MAP sensor to. You should be able to see this when looking under the throttle body as well of course.

The center section of your plenum, between the throttle bodies also appears to be a common area between the throttle bodies. In my mind that would be a better place to tap the hole for the hose barb and pull the map signal versus a single location at a throttle body. The reason is it's an area of the plenum that will see all cylinders. Again, a location that should give the smoothest map signal.

It's important to have a steady, smooth MAP signal if you are running a speed density EFI program logic. If the MAP signal is not steady and smooth it will be impossible to get a good idle or decent tune. The more cylinders the MAP signal is exposed to in the plenum the better. That is why I figured another option would be to Y the two throttle body ports together, then into the MAP with a single feed.

You will also need a manifold port to reference the pressure regulator if you choose to do so. That also needs to be a smooth signal otherwise pressure will fluctuate causing tuning hiccups.
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Old 02-20-2006, 09:44 PM
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Thanks Rick. My first thought was the side of the center section of the plenum. Everyone seemed to have different ideas. The throttle bodies do have the barbs but I have not checked to see if they access all four bores. I will tomorrow. If so that may work for the regulator signal.
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Old 02-21-2006, 03:25 PM
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That port should come out right under the blades, meaning that port would see the signal from all the air coming through the tbody.

All you can do is try those locations. Once you setup the mapping for startup and look at your VE table on the EFI program you will know if the MAP port location is workable. It should show a steady reading in the cell location once the idle fuel mixture and timing is dialed in. Depending on the camshaft it should idle in the 50 to 60 KPA range as a very rough ballpark.

The same situation with the fuel pressure. The pressure at idle should be stable and not wavering.
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