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i know more power, and torq. i mud. cold water, and mud. seems to brake headers all the time. i use my stock manafold. i saw this, and i need new gaskets for the manafolds anyway.
i have a set of heddman headers never used because im swapping a 460 . its comes with gaskets 60$ plus shipping-my email is [email protected] if anyone is intersted
it seems like a great deal, but do they crack/brake in water, and mud?
On a stock or mild 351M headers will give you no performance gain whatsoever. They are literally not worth the hassle.
 

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So how is it that they produce more heat? I know they tend to leak, but if I rebuild my motor I want more flow.
Compared to cast iron exhaust mannys, headers are a bigger source of engine compartment heat because they are thin metal and have a LOT more surface area..AND are often closer to the starter motor to boot. That is why they make header wrap..to keep the heat 'in' the headers.

The power gains from headers compared to the relatively high-performance castings found on the 351m/400 engines to start with are barely measurable in the RPM range of interest for a truck. Claims of 10-20HP improvement from 'just' headers apply to engines like the FE (360/390) or 302/351W, which had crappy exhaust manifold designs in most cases. The 335 and 385 series engines have pretty decent factory exhaust manifold designs, which is why headers are not worth all the hassles they bring to the party, IMHO.

Even the built Aussie-400 EFI in my trail rig has the stock cast iron mannys..
 

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Compared to cast iron exhaust mannys, headers are a bigger source of engine compartment heat because they are thin metal and have a LOT more surface area..AND are often closer to the starter motor to boot. That is why they make header wrap..to keep the heat 'in' the headers.

The power gains from headers compared to the relatively high-performance castings found on the 351m/400 engines to start with are barely measurable in the RPM range of interest for a truck. Claims of 10-20HP improvement from 'just' headers apply to engines like the FE (360/390) or 302/351W, which had crappy exhaust manifold designs in most cases. The 335 and 385 series engines have pretty decent factory exhaust manifold designs, which is why headers are not worth all the hassles they bring to the party, IMHO.

Even the built Aussie-400 EFI in my trail rig has the stock cast iron mannys..
Exactley!

My Aussie headed 400 TBI is also wearing the stock manifolds. Why change a good thing? :beer

If you are looking for more power from a 351M; start with a decent cam, a 4 barrel carb, and a mild dual plane intake like the edelbrock or weiand. For future mods, consider a 400 with higher compression pistons like those from tmeyer or Aussie heads....Or go 460!
 

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Discussion Starter #10
that was pretty much what i thought after doing the search. i hust thought i would ask. . i will just keep the manifolds. thank you.
 
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