Exhaust Manifold Noise
Many who own a 4.0 L V6 Petrol powered Prado complain of an
exhaust noise when accelerating - much like the sound of of an
After thorough investigation with sound probe equipment, the
noise emanates from the exhaust manifolds themselves, particularly
in the area around the point where the exhaust runners exit the
exhaust port in the head and connect to the main manifold duct.
As can be seen from the picture above, the exhaust ports spill
into the main manifold duct at right angles - resulting in a good
deal of "interference" to the flow of each exhaust
pulse. This manifests itself as the noise owners are complaining
about. It should be said that there is no detrimental affect on
the reliability or longevity of the engine.
At this point there is no ready solution. Wrapping the manifold
in header wrap material does assist in insulating the noise (and
heat) however the added heat stress on the manifold itself will
undoubtedly have a detrimental affect on manifold service life.
Most dealers are aware of the problem though at this stage are not
armed with an adequate solution.
As an aside, below is a picture of a 1948 Ford Flathead engine.
The header design of that engine is similar to that of the 1GR-FE 4.0 L V6 Petrol Prado
engine. Incidentally, the exhaust manifold design and construction
is similar to the current 2UZ-FE V8 engine found in the 100 Series