I have a small block chevy motor with an offenhouser manifold and running 6 97's. I need to run a vacuum line for my 350 trans. I can't find any place for a vacuum line, any one else run into this issue? I'm sure I've been thinking about it too much and it's an easy solution but any help would be great. Thank you!!
looks like you need a suitable fitting and drill and tap the manifold for it..an easy job if you have the right gear.plenty fittings available at Summit under manifold vacuum fittings.
"Normally" the factory tapped into the intake manifold for the cleanest manifold vacuum. Anything else...most obviously, you have two choices...the intake manifold or the carburetor...you pick. Mike
My older Offy manifold has the raised location as shown on the above photo. It is spot center drilled. Easy to finish drill and tap.
If you drill it while on the car have a shop vac running sucking up the chips while you drill. Get it right next to the bit when you break through.
What about one of those bolts that has been centered drilled. Saw that on an earlier thread. Said maybe for a corvette are 409.
I was thinking of a hollow stud as well. If I was to drill the manifold (348 in avatar) can I go into any 'runner', or does it need to be in a particular area?
Neil, Does the center carb have a plug in the back at the bottom? I have basically the same tri-power on my '57 Pontiac and mine has the vacuum take off there. KK
Just use a hole off the back carb. I did it on my 348. just make sure the hole goes all the way through! Don't ask me how I know.
Both of these show what we are talking about https://show-cars.com/product/3009 https://www.ebay.com/i/281141971622...kcqyWou57HjSit0OjknPauuYC4kiR1KEaArnTEALw_wcB
Drill the hole with chassis grease on the drill. There ar are attachments for vacuum cleaner hoses or tape a 5-16” tube to it. Grease the tap and check the fitting often. You do to want the threads too deal.
On a dual plane, on can drill a large strategically placed hole into the upper plane, and then go in at an angle with a smaller hole to hit the lower plane. Back to the topic.
Since it's a dead vacuum, meaning no air will be flowing thru to create a vacuum leak like a PCV valve would. Put it where you like that is feasible.
Thanks Koolkat and Tman. The center carb will be used for my PCV. Thats the stud, thanks. I think I'm no going to drill into the manifold at the back of the back carb, (theres a large vertical face on the manifold.)and tap it, assuming it goes thru, i'll be taking the manifold off anyway for an unrelated issue, so i'll check then, if not, the stud is my fall back. Thanks all.
Put a manual valve body in the transmission . No hole to drill. You are dealing with 6 carbs, shifting your trans shouldn't be a problem.
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