As it would happen, my fears and concerns were to be unfounded.
My 4.6 retains the Rover 180 degree dual plane low rise inlet manifold, fitted with the twin SU HIF6 carburettors. Both were overhauled prior to installation, receiving new seal kits, new butterflies without poppet valves, and new floats set to 60 thou.
The inlet manifold remained as per original. Opening out the inside of the tower and the inlet runners was not attempted as the flow characteristics of the manifold would still be largely influenced by the cross sectional area of the rest of the runners which would be untouched. Any improvement in power delivery would be only evident above 4000 rpm, an area which my tall geared automatic P6b would rarely visit.
After the running in period, the original P6B needles and aircleaner were replaced by BBW needles and a new aircleaner with a substantial 3" inlet. Large free flowing K & N airfilters were also installed. Everything had been sized to ensure that there would be no impediment to the delivery of air to the engine. The exhaust system is also similarly sized, with a straight through muffler and resonator, or cannon if you prefer with a 3" outlet. Very deep and bassy.
Running on a rolling road, the needles were polished to match as closely as possible the optimum air/fuel ratio from off idle to redline. Ignition timing was also advanced. With all other variables being equal, on the dyno a 53% increase in power at the rear wheels was seen compared to the 3.5.
The outcome is fantastic,...29mph (9.8L/100km) country running,..better than I ever had with the original 3.5.
My 4.6 is a high torque Range Rover engine running a custom grind high torque cam. For my tall geared automatic P6B, it is absolutely brilliant!
The build and tuning were undertaken at Graeme Cooper Automotive, a Land Rover / Range Rover specialist here in Sydney, Australia.
Ron.
