What I have observed over some years, not just with exhaust manifolds, what the factory or OEM did or didn't do, their procedures or what they could get away with are not necessarily going to work for the DIYer for several reasons.

Another factor is the way some approach tightening fasteners, (nuts and bolts, wheel lug nuts, flanges, water pumps, intakes, carburetors, etc) and here we very often see the real problem. When everything is nice and new, mating surfaces are clean, and true and flat, or near enough. Fast forward 30 or 50 or 70 years, surfaces aren't "true" anymore. The tendency with something that leaks is to reef it down a little more. Or a LOT more. But in the case of warped mating surfaces, it will likely leak no matter what, no matter how tight the bolts or nuts may be.

If you look at exhaust manifolds, the spec is 23 to 28 pounds.. Nice and firmly snug. Tighter is not better! A big thing people overlook with torque specs, is once the component has been properly torqued, they must be checked after so many miles (or heat cycles) and re-torqued (if necessary) to spec until they stabilize at that torque. They will often "loosen up" for a period of time, but they will stabilize. Exceeding the torque spec value, in hopes of avoiding extra time or labor, is likely just going to ultimately result in cracked or broken parts, and you won't have saved any time or money anyway. When I installed Rams Horn manifolds on my Y, I used "gaskets" insofar as the accompanying special aluminum heat shields used with Rams Horn, they stand up even with the top of the valve covers, and the reason here is (I think) to keep excess heat away from valve springs or guide seals, or maybe coking up the motor oil. But it took a while for those manifold bolts to stabilize, maybe 3 to 5 cycles.

The Shop manual has all the torque specs, it isn't a bad plan to go over everything on the engine and transmission and make sure it's snugged up. I find this oddly satisfying, but, then I'm pretty weird.

Hi all, I originally started this thread with the question “ Are exhaust manifold gaskets necessary on a 312?”. I bought a new set of EMs, had a machine shop true the flanges on a belt sander, had them ceramic coated and installed them without gaskets with a “very thin” coating of permatex orange high heat RTV silicone per Ted. I finger tightened the bolts, then snugged them up with a 3/8 ratchet, from the center out, then tighten them up with the ratchet; next it put a torque wrench on them and found I was at 20 to 22 lbs already (shop manual calls for 23 to 28 lbs) I stopped there and fired it up; no leaks, one and done. I will re-torque after a few more miles and publish my experience with the ceramic coating in a future post but when it comes to torque, as the man said “tighter is not better” it’s all about the fit 🚗.

1955 312 T-Bird Warwick, NY