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JeffreyNMemphis 07-06-2007 04:20 PM

Carrera throttle body - manifold pressure signal
Hello pelicans,

Can you please tell me what size tubing I would need to connect the throttle body "boost gauge signal" to my boost gauge?

Thank you Jerry for the picture below.

This is my gauge:

hobieboy 07-06-2007 04:38 PM

Going from memory, I think that is a 1/4" inch

jbrinkley 07-06-2007 05:29 PM

those labels on there have changed for me. i wouldn't know what size tubing that gauge uses. but here's a pic of what I've done, this is below the plate so i can see vaccume also. if you just want to see positive press, you can take the signal anywhere inbetween the plate and the turbo. Like this tee off the WG signal. regular autometer uses 1/8 inch tube
there are no threads anywhere on the TB, it's all improvised.
you just don't want any leaks, and remember, it's LP so really not critical unless you use something that would melt
easier to put pics in a thread than a PM, otherwise I would have

mb911 07-06-2007 07:27 PM

you are useing a vacum gauge off of a cessna(or similar)? Where you going with that? What Brand UMA or westach? it is 1/8 inch hose

Jim2 07-06-2007 07:32 PM

Jeff, you can buy bulk 5/32" rubber vacuum tubing from most auto parts stores. I pay little under $20 for a 50 foot roll. It takes a good number feet to nicely route the line from the rear of the dash to the engine bay. This tubing is near the size of the rubber "T" shown in Jerry's picture.

The auto parts stores also sell small plastic "Ts" and unions which come several to a package for $2-3. They are commonly used for connecting vacuum tubing or window washer tubing. (There is a white one in Jerry's picture) Use one of these plastic "Ts" on the factory rubber T shown in the pic, then you can split to both the fuel pressure regulator and your boost gauge. Use small nylon zip ties on all these rubber connections to try and prevent any hoses from coming off.

Your boost gauge uses 1/8" NPT (national pipe thread). Your auto parts store should have selection bins of brass fittings and hardware including hose nipples from 1/8 npt to 3/16" hose barb.

Edit: you can skip the T which I described above and hook onto the gauge port which is labeled in Jerry's picture, but this port is adjacent to the edge of the butterfly plate at idle, and might display something a little higher in vacuum than actual manifold vac. Boost will be reflected accurately though.

JeffreyNMemphis 07-06-2007 09:28 PM

Thank you all. Hobieboy, Jerry, Jim2...


That is an aircraft gauge from a twin cessna. I bought it on Ebay for $35.00. I got the idea from Jim2. Thanks again Jim! You can see it in his track video where the VDO clock used to be. It is 3 1/8 and fits perfectly in there. With 2 needles, I can get 2 readings... will come in handy to check my plumbing for leaks.

Jerry, the first picture is the fitting into your intercooler?

Jim2, will the 3/16" hose barb give me a tight fit on 5/32 hose? Will the 5/32 hose fit the guage port or will I need a reducer? I am trying to get the pieces together to install in one shot without running back and forth to the auto parts store..

I don't have the BEGI fuel pressure regulator hooked up yet. I want to install the manifold pressure gauge and an LM1/AFR guage before I start putting the turbo kit together.

Jim2 07-06-2007 10:21 PM

Jeff, again, you need a 1/8 npt by 3/16 hose barb fitting for the back of the gauge. You might recall the other thread you posted showing the rear of one of these gauges, will refresh your memory of what you are dealing with. The 5/32 tubing works well with 3/16 barb fittings. Not gospel here, do as you see fit.

My aircraft gauge needed about two wraps of electrical tape to friction fit into the clock opening.

Ben, apparently the actual Cessna gauges don't go to 75 inches, they only go to about 55. I'm told Cessnas and equivalent planes only try to recover pressure loss at altitude, and minimal added boost. In my EFI converion thread someone pointed out that these 75 inch gauges were from DC-6s or other supercharged radial engines from the 50s era. The one I'm using is borrowed, I should probably returm it and locate my own.

JeffreyNMemphis 07-07-2007 12:25 AM


Thank you again. I found many of these gauges to choose from on Ebay from low price of $30 up to $150.

I will take the gauge with me to the parts store. The only part that I am not entirely sure of is the fitment at the throttle body. Venture a guess what size the hose that is hooked on there now is? I guess I can take it off and bring it with me to the autoparts store to be sure... I am going to have to play contortionist to get back there aren't I? <smiles>

JeffreyNMemphis 07-07-2007 12:34 AM

When my engine was apart for rebuild. I took super high resolution photographs of everything from every angle. It has come in very handy for studying things.

David 07-07-2007 04:36 AM

Since the TB has flow through it, it will read a lower pressure (one of the Bernoulli equations.) I read boost for the gauge off the vacuum port:

mb911 07-07-2007 05:43 AM

well if you guys need guages in the future let me know. I use to work for 1 of the largest aircraft parts suppliers in the US and probably the world. This was a former life but One of my best friends got my old job per my request so I still have the good deal option..

jbrinkley 07-07-2007 06:10 AM

Dave, you have me thinking........ below the throttle plate and where your arrow is......... won't they read the same?

mb911 07-07-2007 06:14 AM


Originally posted by jbrinkley
Dave, you have me thinking........ below the throttle plate and where your arrow is......... won't they read the same?
yes they should or very very close.. hey are you home? I was going to give you a call

jbrinkley 07-07-2007 06:18 AM

i am, till tomorrow, laurie took the cable modem though, and the phone with her, call the cell

mb911 07-07-2007 06:45 AM

how long are you gone for?

JeffreyNMemphis 07-09-2007 03:46 PM

Hey Guys,

I got the fittings for the back of the gauge and the tubing... I pulled the clock out.

How do I route the tubing back to the engine? I tried to find a hole to get the tubing down to the floor, but there seems to be some kind of panel that only has a few grommet holes that were not large enough to get my tubing through. Do you drill a hole?

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