Since I work at a computer these days, I've been reading quite a bit on the forum to gain knowledge, make sure I haven't made any mistakes, and find better ways to do things regarding my setup. Something I've come across is to avoid running your internal map sensor vacuum line on a T because it could potentially give your map sensor faulty readings (mine is currently on a T with the boost gauge vacuum line).

Can anyone verify this information? If this is the case, where's a good place to plug in my vacuum line for the internal map sensor? Currently I have my BOV vacuum line on the first (front) nipple of the UIM and boost gauge on the second (rear) nipple. Is it more likely to find a better location for the boost gauge vacuum line and run the internal map sensor line on the rear nipple on the UIM?

After looking at all of the vacuum diagrams for single turbo FD's, there seems to be a lot of blocked off nipples that may or may not be suitable locations for either. I don't like the guessing game so I figured someone on here might have an answer for me (outside of running an external map sensor). Thanks!

 

The factory MAP sensor has its own vacuum line, on the rear (firewall side) of the upper intake manifold near the throttle body. The UIM doesn't have much of a plenum, but pulling from near the throttle body should be better than pulling from the front or rear ports on the side of the UIM (near the turbos and ABS). The pressure in each intake runners is not a perfect 10.000 psi even at full throttle, it will change as the rotor sweeps by and blocks the intake ports. Even when the ports are open the expanding chamber volume will affect the intake runner pressure. I don't know how much the pressure will change as the rotor sweeps through its normal rotation, but I do know the pressure change will be more exaggerated near the intake ports and less exaggerated near the throttle. Boost gauges tend to hide those pulses because they don't need to respond as fast as an ECU. But for a MAP sensor that the ECU might be checking 100 times per second (or faster) it's best to keep the supply vacuum line as smooth as you can.

 

For critical items like map sensors and large blow off valves its suggested they be on their own dedicated vacuum line. Does it matter? Not really. Will you get a skewed reading? No...

It's more for reliability and continuity sake. my preference is to put boost controllers and map sensors on the same T. Whatever the map sensor is seeing is all ruling period. When it comes to external boost controllers, I want it to agree with the map sensor always so I put them on a T always.

As it was mentioned so thoroughly, its possible to get different readings based on where your vacuum line is tapped in. If your map is reading one thing in one place and the boost controller is reading something similar but not the same in another place, it opens up the possibility of having some kind of issue.

So to answer your question, it doesnt matter. Its preference. I would advise testing it yourself just to see.

 

in theory the boost gauge and the Map sensor can share, but i've seen things not be happy. prefer to keep the MAP separate, and use the MAP sensor port on the intake. boost gauge and BOV can go anywhere, they care less

 

All good points. The big thing too is if you need to run a T for a vacuum line, NEVER NEVER run plastic T's. Use brass ONLY. Had a friend blow an engine after the plastic T going to his MAP sensor broke from heat, car ran crazy lean, pop went the engine.

Dale

 

I'm glad you said something because my T is plastic...that could've been bad! I decided to buy some more vacuum line and run the internal map sensor vacuum to the OEM map sensor draws from. Just seems like I'll get a lil more consistency. Thanks everyone!

 

Is there any particular reason why you wouldn't want to run a boost/vacuum block?

 

There are more than enough free ports between the upper and lower manifold that none of us should need to use one...... unless you're using something custom but even then, they have plenty of ports too. Other than the map sensor and boost gauge, how many additional things need to be ran simultaneously where you need so many vacuum ports?

Majority of modern ecus have built in map sensors, mac valves run off the turbo, fpr has a dedicated spot already on the lim, same for the booster on the uim, most run catch cans so the pcv is taken care of, single turbo removes the rats nest....

I have 3 vacuum lines not counting the mac valve. Map, fpr and boost controller since I'm using the profec 2. I can't really see why a vacuum block would be needed in any rew application unless you just want everything getting reference from the same place but even then, the deviation would be minimal. I can understand map and boost control being on the same but with a modern ecu, the map sensor and boost controller ARE the ecu so they will always agree.

 

On an FD there's really no need. There are enough nipples on the UIM to do this.

Those blocks were designed for cars that don't have enough points to tap vacuum or boost into, especially putting a turbo on a non-turbo car.

Dale

 

Some things are common sense/established, like the MAP reading right after the TB for the smoothest signal, but some of this seems overly fussy, possibly even questionable.

Like how does having a boost gauge with electronic sender short tee’d into the MAP line really matter? Especially when compared to the one suggestion of pairing the boost solenoid and MAP on the same line?

Yet if the MAP is king above all then why risk anything else at all on the same line, let alone the boost solenoid? Please don’t misunderstand, there’s not any intention on my part to pick at anyone in particular, but rather only noted to demonstrate why it’s no wonder people are confused and unsure.

A block is fine as long as it’s fed by a sufficiently sized port and supply hose between them to handle all the loads tapped into it, but you wouldn’t want to run the MAP off it as per the first sentence in this post. I’ve seen everything else run off a block successfully though; boost solenoid, boost gauge, Hobbs switch, WI controller, BOV, etc.

Because having a common point and maybe even using colored lines to help distinguish/trace what’s what makes sense to some folks including then capping/clamping/gluing caps on all those other various factory manifold ports that aren’t always so easy to see if there’s a problem there or not.

Yet as we see in this thread; that varies a lot depending on the person and intention. There’s more than one way to skin a cat and they all have pros and cons. Maybe even depending on the mood that day coupled with the position of the heavenly stars it seems.

like brass connections being heavier and more sensitive to momentum forces, so securing them from flopping around needs consideration.

then someone else says use only hard metal lines with compression fittings because even reinforced silicone vacuum hose can burst or come off the connection.

etc. 🤦‍♂️
.

 

Some of the tuners locally prefer not to run the internal sensors at the end of a few feet of hose. In the case here, just used a modern direct mount map sensor

 

For what it's worth, in my own experience with my car, JDM REW manifold, my FPR reference is not stable and does not appear to be accurate at all times coming off the front side of the intake, near the throttle cable area. I ran it off one of the rear ports for a while and everything behaved exactly as expected, but continually hit engine protection through my Haltech ECU when running fuel pressure reference off the front port. I don't think they're all created equally...

 

The stock vacuum source for FPR is the way to go there. It's down on the LIM close to the primary injectors.

Dale