I am guessing 3/8 NPT if the caliper was used to measure the hole? that flared fitting will not seat, those are NPT
It's a 454 chevy. Also Squirrel once there's positive manifold pressure what happens to vacuum advance. Thanks for helping. This is nothing like my TAFC that was easy. Lean until egt got to 1200* Terry aka dirt t
there will still be vacuum at the carb because it is above the blower. hook the vac adv to a port on the carb
That looks like a flare fitting…3/8”? I’d say you need 3/8” male pipe to 3/8” female inverted flare to make that tube usable.
hmmm....vacuum controls like advance and shifting are best NOT connected to the carb. Because when it's making boost you do NOT want vacuum advance, or modulator vacuum. The best answer is use a mechanical advance only distributor, and a manual shift transmission (such as a Th400 with a manual valve body). I played with both vacuum things with my 55 for years with the blown 454, but when I built Plan II, I went full manual/mechanical, and it worked better
Before you buy a 3/8 NPT to -6 fitting try taking that fuel pump to the local hardware store and see if any 3/8 NPT fittings fit. Both the 3/8 tube fitting you showed and a 3/8 pipe fitting have 18 threads per inch but I think the pipe thread will not screw into the pump. Here’s a 3/8 tube nut screwed into its 5/8-18 threaded hole^ This 3/8 NPT x -6 AN fitting has 18 threads per inch like the tube fitting but its diameter is greater.
Not cheap but I think this does the job, my very old Earl’s catalog shows it as item number ES 8490-6-6, Holley uses a new numbering system as shown on the photos. This looks like it will work, maybe someone else will comment.
If you were measuring the internal threads on the pump, you must be aware you were measuring approximately the minor diameter of the thread. For a -6 (3/8) nominal size for both JIC (AN) and inverted flare is .563" which is close to what you measured. If it's a pipe thread, the diameter measured will depend on where you measure it at as it tapers down as you go inward. I don't see a seat for an inverted flare like what is shown in the pic of the fuel filter posted. If it is a straight thread and the surface around the hole looks machined (not just a cast surface) it may be a straight thread o-ring style like the one shown in the last post. It also almost looks like there is a small recess machined in there too (hard to tell by the pic) which would be to accommodate the o-ring. The threads will be the same size as the JIC (AN) style for a -6 size of 9/16-18.
by pic , fuel pimp looks to been cut for O ring , if so JIC , Some Pipe , some Jic A/N How is your 350 built & what mods? If not correct , you will need to look into this or one like it . & you will need to Not run Vac Avance Any thing above rooter going to pull vacuum, Theres ways to make work , requires thinking to do I honestly do not think nobody makes the part at least how I would do it. Below rotor vac , & Spring loaded popet check valve
I modified the BDS PDV, and got it to kind of work...I set it up so it would supply manifold vacuum to the modulator, until it started making boost, then it would provide atmospheric pressure. but you could try just connecting the vacuum hose to the intake manifold and see how it works. You can also put a vacuum gage between the carbs and blower, and a vacuum/boost gage at the intake, and see how the numbers look. Keep in mind that if you're making boost, and the modulator thinks there's vacuum, it will not be boosting line pressure enough to keep the clutches from slipping. Have fun.
I think you want a speedway P/N 6174033. 1/2 20 IF male to -6 AN male double verify with a TPI gauge and you calipers
Looking at that style of fuel pump on Jegs site the ones I looked had pipe threads in the body. If it doesn't have that seat for the flair on the tube to seat on it is not a flair fitting. You can usually distinguish the taper on pipe threads. D Denny's post #14 is something that a lot of us should save to the reference file. Plus pipe fittings are measured by the ID of the pipe not the OD of the threads.
Definitely looks like an "Inverted Flare" fitting ..... you can usually buy IF to JIC(AN) steel adapter fitting from hydraulics suppliers. I use them regularly to convert fuel, transmission, PS connections to JIC(AN) male. This is a sample fitting from SUMMIT, they have a wide variety of sizes and materials etc. https://www.summitracing.com/parts/aer-fbm2964
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