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vortec exhaust manifolds


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Anything above 87 will not be the best choice for many reasons.


75-80 400" Motor home (school bus, some 20-35 series) are 6bolt, high nickel and high flow castings.

Even the manifolds from a 69-77 chevelle, nova or caprice will work better.

80-86 Truck VIN code P, L can be six or 7 bolt and stand up well.

86 truck is almost the last of the 6 bolt early style (the early style was blended out by using the inventory up in the big fleet trucks only - i believe as late as 89 - so unless youre looking in the bus boneyard they are very hard to find above 86).


Manifolds have a tendancy to hold the heat making a thermal barrier to create a dynamic "back pressure". Thats their primary designed function (notice that "header style" manifolding did not come in to factory design until after the computer took full control of the combustion efficiency eliminating the need for a variable "safety valve" in operating parameter control)!


post 87 are low nickel content and will work for the street - but racing will glow red hot and cycle back - causing flaking and warpage. On the street one can follow the factory lead and delete the gasket (assuming a nice flat manifold surface) thus allowing more heat from the manifold to return to the head and thus be cooled by the cooling system. Racing you want to insulate the manifold from your already stressed cooling system (and thus exhaust valves/seats) with a compound gasket - thus putting even more stress on the manifold. Post 87 was made to run with no gasket and as such overheat, flake, warp and crack easily when a gasket is used.

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