Excellegions

I have a 1987 trans am and im clearing the engine bay as much as i can. Im eliminating the entire smog system and i need to plug the 4 holes on each of the two stock exhaust manifolds. On each manifold there were three on the side and one on the top all the way towards the back. It looks like a brass npt fitting would do it. Anyone know what size it couuld be?

UNCLE TOM

iTrader: (1)

1/4" NPT , available at most hardware stores . good luck .

Excellegions

Excellent, thanks, do you believe aluminum plugs will be fine?

DuffMan

iTrader: (1)

probably, but I think you'll find brass before aluminum at a hardware store. use some copper RTV on the threads if you like, just to be sure they are sealed for good

ScottyRock

iTrader: (3)

I used brass plumbing fittings, and it works very good

polygaryd

Lowes has the 1/4-18 npt drill and tap set as well as the brass plugs in the plumbing ilse just in case they break like they did on my car. Had to take the manifolds off Drilled them out, tapped em, plugged em and it works great. All so i could put some nice spark plug wire dividers on.

Tuned Performance

iTrader: (92)

[QUOTE=sofakingdom

The correct plug is not ¼" pipe, although that will usually somewhat sorta kinda almost work for the most part without leaking too bad (that is, not too much worse than most engines with this kind of "maintenance" already leak elsewhere). Correct size is 5/16" inverted flare.
[url]https://www.dormanproducts.com/p-46696-785-452.aspx[/url]

polygaryd

[QUOTE=Tuned Performance;6175055]I took a few of the un broken smog pipes with the threaded ends to lowes and they thread all the way in tight to a female 1/4" npt steel fitting by hand. Im not sure how they'd fit into a 1/4" female threaded piece of steel when they are 5/16" inverted flare... I started the car up and have 0 leaks at the plugged smog tube holes or anywhere else in the manifolds or collectors, at least none that I could see, hear, or feel. Oh and when i chased the threads of the undrilled holes that the tube ends didnt break in, the tap went in without taking metal out like thebthread pitch was different just some of the soot and wasnt loose like its the wrong size. Just saying.

sofakingdom

iTrader: (1)

Because the thread pitch is the same, or at least close enough over the short length involved; and the diameter is close enough that they go in far enough before the straight flare-nut thread bottoms out on the tapered pipe thread, or vice-versa depending on what combination of mismatched parts you're screwing together, especially with all the rust and soot and whatnot, to where they seal more or less well enough that you don't too much notice the difference. Even more so if you spoooooge em up real good with sealer.

They're 5/16" inverted flare.

polygaryd

I guess i wasnt clear, i was at lowes with a brand new steel 1/4npt female adapter with no bottom for the pipe to bottom out on and seem tight. i threaded it in by hand not a wrench, no rust, no goop. 4 of the holes that didnt get the pipes broken off into i chased the threads with the same tap and it had very little resistance vs chasing the holes that i had to drill out. Also the 1/4" plugs used arnt even close to long enough to bottom out and then tighten up because of force vs a good seal. On top of that i had my neighbor who is a machinest that measures and inspects thread pitch, diameters angles, etc all day long for over 30 years. He was the one who found that 1/4 npt would work, also he said that the end you call a flare (and i agree it looks like a flare but im not a machinest) is not tapered like npt but the female side is tapered which seems to be true in this case. Regardless other ppl in this thread have said 1/4npt and I have perfect results with it also. Youre saying it only works with a lot of force or goop or whatever but that's not true regardless of whether youre right about the diameter and thread pitch.

1/4"-18 npt doesnt just kinda sorta work as you stated, it works perfectly with no leaks, no extra sealing provisions needed. Im trying to help other ppl know where to get the tools and materials they need to do this job, youre telling them it doesnt work well when it does work just fine.

sofakingdom

iTrader: (1)

They're 5/16" inverted flare. PERIOD. That's the reality.

¼" pipe is close enough that it will screw in... it's not "right", but it's usually "close enough".

I didn't "tell them it doesn't work well"; what I DID say was, the right size is 5/16" inverted flare (that being what the tubing is), but that ¼" pipe is "close enough" to work in most cases. Please don't put words in my keyboard that I never typed.

There's a difference between RIGHT, REALITY, etc. on the one hand, and "close enough to work" on the other. I'm a bit of a perfectionist myself, I prefer to get things RIGHT when practical.

In this case, RIGHT is 5/16" inverted flare, but ¼" pipe is "close enough to work most of the time". If that worked for you, then, great.

Drew

iTrader: (58)

Why do people bump a six year old thread just to post some dumb stuff?

Yes, you can cram any old garbage in the hole. If you want a fitting that exactly and properly replaces the AIR fitting and seals on the flare instead of the threads, it's an inverted flare fitting.

polygaryd

[QUOTE=Tuned Performance;6175055]
That isnt telling ppl it works its telling them it doesn't work well like i said you said