Olds intake manifolds have huge crossover exhaust passages right next to a
cold fresh air/fuel passage. Other GM cars have crossover exhaust passages
but, they are much smaller than the olds. The olds has what is commonly
called a siamese center exhaust port with a huge passage through the center
of the cylinder head that connects to the intake manifold. I have several
NON TORONADO intake manifolds in my shop that are not dropped carb flange
intakes. They show cracks on the floor of the manifold just like the
toronado manifolds do. One of them I used for welding practice using
different methods and from that futile experiment (unsuccessful )
determined that they are generally NOT WELDABLE. So, block off plates are a
workable solution.
Other GM intake manifolds that are made of the same alloy of cast iron
(low nickel, low molybdenum, high carbon content) are also prone to
cracking. The high nickel content of the engine blocks themselves provides
some protection against cracks, in my experience. Just the way it is, I
guess.
Jim Hupy
Salem, Or
78 GMC ROYALE 403
> favor and stop reading the "hot rod Oldsmobile forum".
> 455 Oldsmobiles used in GMC"S have a huge load on them compared to a
> 4-4-2 or a Cutlass Supreme or a Toronado.
> The exhaust gasses from a GMC are much greater in volume as well as
> temperature, due to the 12,000 pound weight of the coach. The coolant and
> oil temperatures are much hotter as well. These extremes are what Crack
> manifolds.
> Jim Hupy
>
>
> I don't.
> I agree its a far higher load. However , I dont recall a problem with
> cracked intakes on SOBs with chevy 454s which have even heavier loads and
> far
> worse aerodynamics. Do they have a heavier cast manifold?
> I dont recall them looking much different than passenger or truck manifods
> other than the 'Peanut port' size.
> Exhuaust manifolds are another story entirely.
> --
> 76 Glenbrook
>
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> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
cold fresh air/fuel passage. Other GM cars have crossover exhaust passages
but, they are much smaller than the olds. The olds has what is commonly
called a siamese center exhaust port with a huge passage through the center
of the cylinder head that connects to the intake manifold. I have several
NON TORONADO intake manifolds in my shop that are not dropped carb flange
intakes. They show cracks on the floor of the manifold just like the
toronado manifolds do. One of them I used for welding practice using
different methods and from that futile experiment (unsuccessful )
determined that they are generally NOT WELDABLE. So, block off plates are a
workable solution.
Other GM intake manifolds that are made of the same alloy of cast iron
(low nickel, low molybdenum, high carbon content) are also prone to
cracking. The high nickel content of the engine blocks themselves provides
some protection against cracks, in my experience. Just the way it is, I
guess.
Jim Hupy
Salem, Or
78 GMC ROYALE 403
> favor and stop reading the "hot rod Oldsmobile forum".
> 455 Oldsmobiles used in GMC"S have a huge load on them compared to a
> 4-4-2 or a Cutlass Supreme or a Toronado.
> The exhaust gasses from a GMC are much greater in volume as well as
> temperature, due to the 12,000 pound weight of the coach. The coolant and
> oil temperatures are much hotter as well. These extremes are what Crack
> manifolds.
> Jim Hupy
>
>
> I don't.
> I agree its a far higher load. However , I dont recall a problem with
> cracked intakes on SOBs with chevy 454s which have even heavier loads and
> far
> worse aerodynamics. Do they have a heavier cast manifold?
> I dont recall them looking much different than passenger or truck manifods
> other than the 'Peanut port' size.
> Exhuaust manifolds are another story entirely.
> --
> 76 Glenbrook
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
