Warped exhaust manifolds

[DanAR]

I’m sure if I guy went through the old threads enough I could find the answer to this but the threads seem voluminous. Cast iron exhaust manifolds have always been subject to warping as long as I can remember. I got an exhaust tic from one in my first car, a 64 Sport Fury in the late 60s. A lot of the time it was due to manifold bolts loosening and backing out - sometimes simply retorquing the bolts would take care of it. If not then, machining the manifold, adding a gasket (most manufacturers did not use them) or some red, high temp RTV solved the issue. But I keep reading about seized and broken bolts when I read threads on the RAM bout warped manifolds. That’s new to me. If a bolt breaks and clamping force is lost on a portion of the manifold I can understand the manifold warping. But why are the bolts breaking. Are they just plain using weak bolts? Over- torquing during assembly? What’s going on here?

 

[chrisbh17]

I’m sure if I guy went through the old threads enough I could find the answer to this but the threads seem voluminous. Cast iron exhaust manifolds have always been subject to warping as long as I can remember. I got an exhaust tic from one in my first car, a 64 Sport Fury in the late 60s. A lot of the time it was due to manifold bolts loosening and backing out - sometimes simply retorquing the bolts would take care of it. If not then, matching the manifold, adding a gasket (most manufacturers did not use them) or some red, high temp RTV solved the issue. But I keep reading about seized and broken bolts when I read threads on the RAM bout warped manifolds. That’s new to me. If a bolt breaks and clamping force is lost on a portion of the manifold I can understand the manifold warping. But why are the bolts breaking. Are they just plain using weak bolts? Over- torquing during assembly? What’s going on here?

Weak bolts and not necessarily large enough diameter.

OTOH, at least they aren't strong enough to rip out of the head.

 

[Torqued]

I’m sure if I guy went through the old threads enough I could find the answer to this but the threads seem voluminous. Cast iron exhaust manifolds have always been subject to warping as long as I can remember. I got an exhaust tic from one in my first car, a 64 Sport Fury in the late 60s. A lot of the time it was due to manifold bolts loosening and backing out - sometimes simply retorquing the bolts would take care of it. If not then, machining the manifold, adding a gasket (most manufacturers did not use them) or some red, high temp RTV solved the issue. But I keep reading about seized and broken bolts when I read threads on the RAM bout warped manifolds. That’s new to me. If a bolt breaks and clamping force is lost on a portion of the manifold I can understand the manifold warping. But why are the bolts breaking. Are they just plain using weak bolts? Over- torquing during assembly? What’s going on here?

From what I’ve read is that the design of the Manifolds is the problem. Where the exhaust gases exit out of one side, the temperature is much higher at the cylinder 7, 8 ports, than the previous ports. The different expansion rates of cast iron, and Aluminum is one thing, add in the temperature difference across the manifold. That makes for a lot uneven expansion. From what I put together after reading multiple threads, and posts from different forums is that the bolts that are most likely to break are the ones for cylinders 7, 8 the hottest section , so likely the excess heat, and the force from the expansion and contraction weakens the bolts. Many Hemi owners are going with a good quality set of shorty headers and remflex gaskets. I hesitated going this route because I remember my father telling me that back in his youth working on the Novas and Chevelles that keeping headers from leaking was near impossible. So I currently have a set of BD Power Exhaust Manifolds being shipped to my house. I ordered them before I started reading into people using headers, and how far headers have come since my Dad’s Hot Rod Days. The headers make sense to me as they don’t combine the heat to one part of the sealing surface. I guess if the beefier manifolds don’t workout , Ill. Go the way of the header. I hope this helps answer you question. I’m by no means any kind of an expert.