MAP Hose Diameter?

[MrN2OBelvedere]

Hello All,

I am in the process of building my intake setup for my project and I need to know what diameter hose should I run from the vacuum port to the MAP sensor? The reason I need to know is because I need to order a weld on bung for my manifold and I need to know what size nipple to use for the bung.

Also, do you have any recommendations on MAP and IAT sensor placement? This intake is a single plenum Tunnel ram style setup for a V8. I was considering placing the IAT and MAP sensor vacuum line on the back face of the plenum to keep things looking sanitary. Is there any reason I should consider another location?

Thanks for your help!

[Matt Cramer]

1/8".

I would put the MAP sensor tee on the plenum, but the IAT before the throttle body. An IAT in the plenum is more likely to heat soak and read hotter than the incoming air temperature.

[NeedTurbo]

If you use a larger diameter line running 10 ft then reduce it's diameter just before the map could this cause a artificially high map?

[Mike_Robert]

If you use a larger diameter line running 10 ft then reduce it's diameter just before the map could this cause a artificially high map?

That's a very good question I've heard several times. Short answer: No. There is nearly zero actual gas flow in the MAP line. The only thing it's transmitting is pressure changes which move at the speed of sound. Even if it were flowing gas, the pressure on the far side of a restriction is less primarily due to friction loss. There are quite a few factors involved in the physics of compressible liquids (gasses such as air) when they are flowing in a closed volume. Since there's almost no flow in the MS MAP line case, you have negligible effect from any of them. Matt's suggestion of 1/8" works very well for many people.

-Mike

[Minami Kotaro]

I use 1/8" OD hose

[Ollie8974]

One more tip on tubing. Dont use rubber hose, especially on long runs. Rubber, over time will deteriorate. All newer cars have plastic tubing installed. Most auto parts stores will have replacment tubing.

[MrN2OBelvedere]

1/8".

I would put the MAP sensor tee on the plenum, but the IAT before the throttle body. An IAT in the plenum is more likely to heat soak and read hotter than the incoming air temperature.

So if I have a cold air tube running up to the throttle body then it is still ok to place the IAT in front of the TB?

[Matt Cramer]

Yes, it is.