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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 exhaust leak.

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 Land Cruiser.


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