npt thread size on chevy 350 TBI?

Boonie Buster · Feb 7, 2008

Ok, I am trying to figure out what size NPT, for the fuel lines coming on/off the TBI carb are on a '91 Chevy 350 ???:eeek: I just want to buy a couple straight forward AN to NPT adapters, but i'm not sure what size the threads are on the TBI system. Anyone know or can point me in the right direction, I'm trying to complete an order, but i'm not sure what to get:corn: I want to say 3/8" but i think that is wrong...:eeek:

Crash? you're the GM guy:kiss:

Blueleader · Feb 8, 2008

It's not a NPT into the regulator body. Normally, the line has a special flare with a funky plastic o-ring seal and a retaining nut. I think it's called a Saginaw fitting?

I tore apart a mid 80's caddy one time with factory adapters on the feed and return lines. It threaded into the regulator on one end and had an inverted flare fitting on the other. It worked great for my setup but have never managed to find another set.

Boonie Buster · Feb 16, 2008

UGH! OK, so it's an oddball size then? anyone else have any input? or experience...?

I am just curious if they make an -8AN to Saginaw/whatever adapter piece for it... I know there are a ton of -8AN to NPT and whatnot thread adapters out there...

Trevor · Feb 16, 2008

http://www.russellperformance.com/mc/adapt_fit/fuel.shtml

go to this link. Scroll down till you see "RUSSELL GM TBI ADAPTER FITTINGS" (the adapter next to it is silver). Those are what you need. I have never seen them in -8 though. Doesn't mean they don't exist, I just haven't seen em.

The russell part numbers are 640800 for the return, and 640810 for the pressure.

Boonie Buster · Feb 16, 2008

AWESOME! thanks, i MIGHT be able to adapt the two...kinda hokey though in my opinion, but at least that gives me a starting point...:awesomework:

edit: after looking at them I could just get a different size (as in -6AN fitting) for the connecting ends of my fuel system, make it all -6AN as I can't imagine it needing to be -8AN if it's -6AN from the TBI, so I can just step down the size right off the gas tank from -8AN to -6AN and run -6AN stuff to the front...cheapeer and easier...