[phoenix]

Thanks once again Rob.

That's really interesting.

I read that one of the final developments of the FJ engines was the XVII for which Cosworth converted the head to 'downdraught' from sidedraught by boring the head and brazing in more vertical replacement inlet ports. This was the first Cosworth to develop over 100 BHP/Litre and it looks like the SCA-C engines were a further development of the ideas explore with that engine.

Downdraughting the ports to the vertically installed inlet valve shallows the angle between the valve and the port and in doing so opens up the 'short side radius' which will improve flow through the port, delaying the onset of turbulence in the port and allowing higher inlet gas speeds to be achieved. The inlet valve size (1.45") in a sidedraught head would flow a maximum of about 128 BHP. In a 'hemi' style crossflow head the same sized valves would flow closer to 142 BHP due to the better port/valve angle and the better position of the valve exit relative to the cylinder wall. It would appear that on the SC engines the head can flow 5-8% more than the best side draught port arrangement could achieve.

I imagine the inlet port sizes are quite large due to peak torque being at 8000 rpm in the 997 cc engine. If this is the case it might have made it necessary to reduce the exhaust port diameter as a compromise in order to fit the large inlet ports into the space available. The plus side of this might have been improved scavenging; the peak torque of 76 lb/ft suggests a VE of around 114% was achieved, and that would not be possible without excellent inlet and exhaust manifold tuning.