Hi Mikael,
my car is number 2061 so the early build before the motors were moved back in the series 2. My original headers looked like a special fabrication - mild steel flange and short pipework.
I had exhaust leaks from the time I got the car. Because of the 4V heads, there is very little area around the ports to allow much pressure on the gaskets. With a 10mm thick flange the 2 studs would not apply enough pressure on the opposite corners of each port. As a result the car used to develop manifold leaks frequently.
And as you know it is very testing to access the manifold bolts in this vehicle. After many times removing and replacing the gaskets I needed a much stiffer manifold. Fabricating new headers would still rely on a 10mm flat flange, with no additional stiffness contributed by the pipework. What I needed was a cast iron assembly, which is much stiffer and less prone to deform when bolted up. The flanges are about 30mm thick.
There were no cast iron manifolded 4V clevelands sold in Australia, so with my exhaust guy we modified a set of 2V manifolds (very cheaply available 2nd hand). They have the same bolt pattern but the exhaust outlet on the right hand bank needed to be cut and turned to point out to the side. The cast iron was cut and carefully tig welded into the new position.
Obviously the ports on the 2V manifold were smaller than the 4V heads, so we took a standard mild steel 2V header flange (10mm thick) and I port matched it to the head side.
This flange is used like a thick gasket. The work took many hours with a die grinder, but I ended up with an arrangement that has not leaked and has been on the car for around 15 years. Instead of gaskets I used RTV silicon.
The LHS photo shows the flange clearly, and that there is plenty of room for the pipe joint. The RHS photo shows there was no room for the pipe which is why we welded it up.
hope this helps
Peter
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