Boost gauge fitting - what size tap?

[Spooled-up]

I got stuck on my boost gauge install before I started today. The local hardware store couldn't help with the tap for the fittings I have.



Are they npt threads? If so, how do I tap the hole I drill in the intake? I was thinking of just tapping a hole for the smaller fitting to go into and not using the larger nipple.



Is there a special tap for this type of fitting?



Here's a pic:

 

[Thomas]

I'm betting on 1/8 NPT for the smaller fitting. Take the fitting to your local hardware store, check the thread size, and get a tap to match. Also get the appropriate size tap drill.



Be aware that pipe threads are tapered—the further in the tap is turned, the further in the fitting will go.

 

[Evan A. Beck]

The smaller fitting you have is 1/8" NPT, and uses an 11/32" drill. The larger fitting you have is a 1/4" NPT to 1/8" NPT bushing. You won't need it--just drill & tap for the 1/8" NPT.

 

[SlyBones]

Use Piers turbo boost fitting, and dont drill and tap anything.

www.piersdiesel.com checkout the products page. Click on the link to see one installed.

 

[Turbo Thom]

What? I didn't know you had to tap for the boost gauge. I just went in at the side of the block. What in the world am I reading on the gauge ? There was a little plug that had to be taken out.



Whats going on?



. . Preston. .

 

[dalton4]

Preston, our air intake manifolds had a plug that we removed for boost gauge connecting. The 24 valve intake has different size plugs and plug locations (someone correct me if I'm wrong). I'm sure you're seeing boost pressure.



Jerry

 

[dresslered]

DMKelley-

Looks like you are showing the fittings similar to the VDO boost gauge. As Evan says, you've got 1/8" NPT and 1/4" NPT. Go for the 1/8" tap and if you mess it up, then you can step up to the 1/4".

 

[Spooled-up]

So a tap for npt is different than a tap for a regular machine screw?

Where's the most common place I can find one of these taps?

 

[SLang]

NPT taps are different from regular bolt taps. As stated before they are tapered. The fitting does not get tight because it bottoms out such as a bolt or nut. It tightens into the threads so that it does not leak.



You can get the taps anywhere. Lowe's, Home Depot, or go to a auto parts store. They are very easy to find, just ask for one.



Scott

 

[illflem]

Sometimes in hardware stores they are in the plumbing dept. If all else fails try Grainger

 

[BigDaddy]

DMKelley,



You can use a 1/8" or 1/4” to 3/4” bushing with your current parts and install at the manifold, instead of tapping the intake horn.



See Diesel Injection Service’s instructions for Installing Boost Gauge on the 24 valve Engine.

 

[me4osu]

Boost pressure tap

If the tubing is hooking up to a mechanical gauge, I recommend tapping the backside of the air horn. The mechanical gauges have been reported to vibrate due to pulsation when mounted in the intake plenum. The air horn is further away from the valves (so less pulsation) and will still give an accurate reading of boost pressure, because there is no restriction between it and the plenum. Also, remove the air horn when you drill and tap, so you don't get shavings in the engine. All I did was buy an new gasket for where it mounts to the grid heater, but mine came off without ripping the old one.



dresslered has a good idea. You have to be careful tapping aluminum, its like buttah.