False air
For a lot of cars you can buy spaghetti manifolds. They are mounted instead of the standard exhaust manifold. That provides extra power and at least a better sound. The car will in most cases also run better through.
When converting MG B's from American to European specifications, I often used those manifolds because standard manifolds were not always available. But at some point the new sports manifolds turned out to be crooked. After assembly it was almost impossible to get them mounted tightly against the cylinder head. As a result, false air was drawn in and the engine no longer ran on four cylinders. It turned out to be a production error and therefore the problem occurred several times. It was therefore not surprising when there was another car with a freshly mounted manifold that did not run smoothly, that the blame was again shifted to the new exhaust part. When everything had cooled down, dismantling was quickly started to find out that a body washer had come over the stud between the manifold and the cylinder head. Nobody knew what that ring did there or how it had come about. But it was obvious that it did not belong there. Why did this bodywork ring have such a disruptive effect? Because both the exhaust manifold and the intake manifold could not be pressed together against the cylinder head by a thick ring. As a result, a lot of false air was drawn in and the engine no longer ran on four cylinders. When everything was mounted again, without the disturbing factor, the engine ran perfectly.
Text and photo: Jacques van den Bergh
Fake air through the exhaust manifold?
When converting from US version to EU Specs, it is usually a new intake manifold with a double carburetor and there may be false air (between the gas valve and inlet valve) leakage.
A leakage from the exhaust manifold blows exhaust gas out at a non-designated area but does not suck when the valves work.
Peter thanks for the explanation! Because the newly mounted exhaust manifolds were bent, the intake manifold was also not pressed properly against the cylinder head. As a result, false air could be drawn in.