Is it 3/8"? I want to buy a couple of cooling fan switches and 70 amp relays for my 88.

 

This figure lists the diameter at the top of the hole, which you should be able to measure. A little under 3/4" will be 3/8 NPT. A little over 3/4" will be 1/2 NPT.

 

Mine are 1/2" NPT on an Edelbrock Performer 455.

 

 

I Imagine the SBO version is the same.

 

Some Teflon tape or Paste needs to be installed on any of the NPT fittings that thread into the intake manifold. Use the Teflon tape/paste on the first couple threads of the NPT fitting before the fitting is installed.

Do not use a torque wrench on NPT fittings. Use some Teflon tape/paste on the first couple threads of the NPT fitting. Install fittings into the intake manifold hand tight, then with a couple fingers on a box end wrench lightly snug up fitting. Use caution when tightening up NPT fittings, they have tapered threads and if over tightened can crack the intake manifold.

 

Thanks for the pic. I have had 0 issues with leaks on the fittings. Just need to find a thermal temp sensor for the electric fans that don't constantly die. As said teflon tape and acceptable torque is the answer for leaks.