Hole size for vacuum port on an intake manifold

[Bird911]

I have purchase a Jenvey ITB kit for my 3.4. The intake manifold is coming with bumps that needs to be drill and taped if you elect to use a vacuum port. I understand I will need to drill two holes; a smaller one that will go all the way through the manifold for the air to be sucked in, and a larger but shallow one that will be taped to screw the vacuum nipple.

My question is what size do the small hole needs to be ? The tip of the nipple is 1/8’’ I.D. but is this too big ? I got the nipples at my local hardware store as they seem to be the good size and I could not find any specially made for this application. Feel free to tell me if I’m not using the correct nipple.








Thanks,

[Bird911]

Anyone ?

[SoyRacer]

On the last ITB setup that I did we drilled 1/8 pilot holes and then drilled for the fitting. Being that they are tapered fittings I usually drill all the way through so that I can run the tap through. Tapped all six and ran the hoses to a manifold for a MAP sensor. Have also used it as a vac port for brake booster.

[Bird911]

Thanks SoyRacer. I will also use them for MAP sensor and brake booster.

[MetalDoc]

I took the manifold down to the student machine shop and they drilled 3/16" holes for the ports, followed by drilling and tapping for the pipe threads. The engine is out of the car so I have no idea if this is the best solution. How are you going to connect the throttle linkage? I replaced the linkage in the tunnel with a cable.

Paul

[Bird911]

Thanks Paul, I will try to do the same as you. Your tapped hole also seems to be 1/8 NPT, same as my nipple tread.
My engine is also out of the car, and I still don't know how I will connect to the throttle linkage. There was a cable included in the kit but it is way to short. I will need to think about this one.

Are these copper nuts on the intake studs ? any reasons to use these ?

[MetalDoc]

Hugo,

Most of the hardware store nuts are too big 14mm? I think these are 12mm which bolts down without hitting the manifold. I chose these nuts for the size. There is not too much torque on them so copper should work. I think these nuts are copper plated?

Here is a link to the cable install. My project has dragged on so I have not put the engine back in to connect the other end.

Paul

SC Project

[Bird911]

Paul, Yes I remember seeing your thread. Great project, I am also going through all the same steps with my project.

This is another thread I found regarding the linkage replacement with a cable. I would like to go directly from the pedal to the ITBs.

Early 911: Replacing Throttle Linkage with Morse Cable?

[MetalDoc]

Hugo,

I liked the Morse cable, but I couldn't figure out what length to get. Hopefully, the cable I have installed will work. The springs on the Jenvey are pretty stiff.

Paul