L6 250 Exhaust Manifold to Downpipe Question

[John in OH]

I’m currently replacing the intake/exhaust manifold gasket on a 1972 GMC C10 with the 250 L6 engine.

The exhaust manifold to downpipe connection is giving me fits. When I bought the manifold gasket kit it came with a doughnut gasket, but from other postings here, I don’t think my connection requires the doughnut. And after several hours of trying, there is NO WAY this connection can be made to work with a doughnut! My pipe looks kinda like this:



The cast face of the exhaust manifold has two studs and an internal chamfer so it “appears” that the downpipe may fit directly into the manifold without the doughnut. There is a clamp flange that slides on the downpipe and pulls the downpipe up against the manifold face via the two studs.

But I can’t believe that this metal-to-metal contact won’t leak! Am I correct? Will it probably leak? The old studs are questionable so I hesitate to torque them too much. Has anyone used a gasket of any kind, or high-temp sealant to assure a leak-free connection?

[Gmc.guy]

I am putting my 250 together as well and I have to find a down pipe and flange. So I'm watching this one It might seal Try to get it as square to the opening as you can

With that style flare you might have to trim the end halfway in the "bubble" so that it's a trumpet tip or flare for the donut to fit

[Grumpy old man]

While you have it apart remove the old exhaust manifold studs and replace them , if they snap off grind them flat and drill and retap them to install the new studs , oriellys carries the 3 stud package for small blocks and the drills and tap all of it less than $20.00 with new exhaust manifold gaskets , the replacement pipe you have pictured doesn't use a donut but must be torqued up tight to prevent leaks .

[old Chevy guy]

Like grumpy said. New studs,here's your chance while its apart. That is not the same type of pipe as the origanal. While it's off clean up where it seats with a wire wheel or some sandpaper. New studs and crank her up tight and it should be fine.