hey, i got a boost gauge today, its the kind with the threaded fitting that i need to put into a vacuum source. does anyone else have this kind? is there a plug that can be unscrewed on the intake manifold or will i have to drill?

 

My boost gauge, a Stewart-Warner, came out to a 1/8" NPT as you descibe. ACE Hardware (or similar) can provide you with a brass adapter to go from 1/8" NPT to a 1/8 or 3/16 hose barb. This is a fairly common specialty plumbing fitting. Forget Home Depot or Lowes for this, you need a proper Hardware Store.

 

well if i get that with the hose barb, how will it work with the very small diameter nylon tubing that came with the gauge?

 

typically there is only one threaded boss for the gauge itself, then the tubing just gets teed into a vacuum line off the manifold.

If yours has a female threaded end for the source, then get a 1/8" (assuming) brass slip-on fitting so you can put a vacuum line directly on it.

or cut it off and tee like normal.

or post a pic so i can see exactly what you are talking about.

 

The narrow plastic tubing uses compression fittings (a little brass cheerio that gets smooshed between the nut and the fitting, in technical terms).

You probably cannot put an NPT threaded nipple on the gauge, though sometimes the compression/pipe/flare stuff happens to work out okay.

My boost gauge kit came with an compression->NPT adapter. Unscrew an unused vacuum nipple from the intake manifold, screw the adapter in the hole, and use the compression fitting.

 

heres pics and how they connect, yea its the compression fitting. I was thinking tho, if i unscrew the unused nipple behind the throttle body, will that be big enough for the threaded fitting?

 

You want to plumb into the plenum for accurate readings. Immediately post TB might not be the best spot. I'll defer to people who actually do more under the hood than dream (me) tell you about that though.

The fitting dead center in the middle pic with threads on both ends and a hex in the middle is the one you want to screw into the manifold.

However, I bet you could just cut the white tubing someplace convenient and just slip/shove/force some normal vacuum line over it. Secure it with a small zip tie (red of course) in lieu of a hose clamp. Then you can T into whatever line you choose.

 

Do yourself a huge favor and ditch that crappy tubing it came with. Go buy yourself 10feet of 5/32" ID silicone tubing and a hose barb (I think the thread size is 1/4" for the back of most gauges). Use the tubing for the boost gauge, wastegate, MBC, MAP sensor, AFPR, and anything else you need to run a vacuum line to. Check out the pic of where you tap into the manifold for a source. https://www.miataturbo.net/forums/at...8&d=1156711298
On the front of the manifold there should be two taps right on top of the throttle body. If you've got cruise control, one of them is used for that, and the other is used for (I believe something to do with cold idle)... but you can see in the pic that he's tapped off one of those feeds and is T'ing it several times to run lines to various things. You can also see his boost gauge using the stock gauge hardware is tapped on the actual charge pipe just be for the TB.

There is also another small tap on the back of the intake mani that is used for the stock AFPR. The large tap in the middle of the mani is used for the PVC valve source. The very large tap on the very back of the mani is used for the Brake master cylinder.

This pic shows tapping off the source for the brake MC using the stock hardware. https://www.miataturbo.net/forums/at...0&d=1158374647

Here are a couple more pics I made for another post:
https://www.miataturbo.net/forums/at...0&d=1156995178
https://www.miataturbo.net/forums/at...1&d=1156995187

My setup will utilize a tap built into the compressor housing of the turbo for the MBC and Wastegate. But you can see the spare tap (I don't have CC) in both of those pics.

 

Very helpful! Thanks samnavy!!

 

i just took the plastic tube end for the source, ziptied a vacuum line on it, and teed that into the intake manifold.

 

Sorry about this old thread revival, but how well does slipping rubber vacuum line over the harder nylon line hold up? does it not slip off?

 

In my experience it has slipped off. You can always use brass t's. They always worked for me with the nylon lines

 

it wont slip off if you clamp it. or put some silicone/sealant on it before you slip it in then clamp it.

this of course assumes you get the right silicone line to plug this into. if the ID is much larger then the hardlines OD then you need to rethink things