I want to take my exhaust manifold apart from my muffler pipe. There is a triangular flange at the joint where they are joined and I was wondering if there is a type of donut gasket there. I think I have a lifter noise and I noticed that some of the people on the forum said that an exhaust leak sounds just like a bad lifter. Well, I did find an exhaust leak on the same side I hear the lifter noise. Thanks in advance.

 

I just yanked my manifolds and can definitely say that I did not have a donut gasket there. Just a flare type fitting. If it is leaking try to tighten up the nuts a little. May need to spray with WD 40. Good Luck.
I couldn't bring mine into the muffler shop yet as planned but the 'Bubba' Beer can exhaust isn't leaking on my vette at the moment but can't drive it anyway without an accelerator cable. First stop exhaust. Second stop upper controlarm bushings and 4 wheel alignment.

 

The stock exhaust tubular manifolds on the '81 do not use gaskets of any kind. It's a direct-mate fit between the spherical outlet from the manifold and the flared opening into the Y-pipe. If either the manifolds or the Y-pipe have been off the car, there is a chance they may have been dinged up a little, which will cause sealing problems. If no dings are apparent, simply cleaning the sealing surfaces up with some sandpaper or a wire brush (a wire wheel in your drill works very well) should make them seal adequately.

Regarding the noise you suspect as an exhaust leak: Yes, it is common to hear a noise that sounds like a bad lifter, only to discover that it is an exhaust leak. Been there, done that. However, when this happens it is probably the manifold-to-head seal that is leaking, rather than the manifold-to-Y-pipe seal. Think about it: if it sounds like a lifter, then you're hearing an event from one cylinder, not four. If your manifold-to-Y-pipe seal were leaking, you'd be hearing from all four. Besides that, it is simply much more common for the gasket between the manifold and the head to begin to leak a little and then to burn out.

To diagnose: start the engine, let it idle, and get a mechanic's stethoscope or a piece of hose about 3/8" in diameter, maybe 3 feet long. With the stethoscope or hose in your ear, move the other end around the engine, close to where the manifolds bolt onto the heads. You'll find which one is leaking pretty quickly.

If it does turn out to be that gasket, you can get a set of Fel-Pro gaskets that have slots instead of holes for the bolts, so you can slip it in between the manifold and head without completely removing the manifold. It's no big deal on the D-side, but the A/C makes dealing with the manifold on the P-side a real PITA. If your leak is on the P-side, you can loosen the bolts enough to get a thin-blade knife back there and clean the old one out. Then drop the new one onto the bolts and cinch 'er back up. Worked for me.