Straight Port Cylinder Head (SP) project for a Jaguar XK engine
Recently we were contacted by a new client in South Africa to order one of our race spec Jaguar XK Straight Port Cylinder Heads (SP). The Jaguar XK engine was produced in various iterations from 1949 to 1992, with several different cylinder head designs used throughout the years. One of the most popular high-performance cylinder heads for the XK engine is the "SP" (Straight port) head, which was developed by Jaguar in the 1950s for racing and high-performance applications. The SP head features larger valves, revised port shapes, and a more efficient combustion chamber design compared to the standard XK head. The straight Port cylinder head allows for better airflow and performance compared to some early cylinder head designs. This cylinder head will be used on our client’s D-Type replica pictured here at Simola Hillclimb.
To begin, we agree to bring the donor cylinder head up to a race-spec configuration. This was achieved by aqua blasting the cylinder head to deep clean it and this ensured any Carbon, Oxidation and Corrosion was removed and ready for rebuilding. After the aqua blast, we began by fulfilling a large list of updates to the cylinder head such as replacing the valve seats for inlet and exhaust with a new lead-free version to ensure it doesn’t wear out as much in the future. This matched the new high-performance competition spec valves which are larger than the standard ones, improving airflow and engine performance. We cut all 12 valve seats to ensure a precise fit for these bigger valves.
After replacing the valve seats, we also replaced the tappet guides with new bronze ones to ensure its durable and provides a smoother operation. During the project, we had to complete some adjustments and repairs to the old exhaust studs. Additionally, some of the spark plug threads were damaged, so Time-Sert inserts were used to repair them. These are strong thread replacements that ensure the spark plugs fit securely and prevent future issues.
Some other adjustments we made to the cylinder head include improvements to the camshafts which were upgraded to high-lift camshafts, so the valves open higher and for longer durations, improving airflow into and out of the engine, increasing the amount of power produced. One of our top restoration technicians carefully installed the valves and assembled the cylinder head, following the correct procedures to ensure everything fits and functions properly. After the valves were installed, we adjusted the valve clearance to match the race specifications.
Before it was installed the cylinder head face was skimmed flat to ensure a perfect seal and prevent head gasket leaks and the front of the aluminium head was polished for a clean look. After that, the head was painted gold, which is the standard colour for 4.2L Jaguar XK cylinder heads. This keeps it historically accurate and gives it a factory-fresh appearance. Once all the necessary studs were installed, the SP head was fully assembled and ready for installation on the engine.
The SP head is a relatively rare and sought-after component, as classic Jaguar specialists at P&K Thornton Restorations we have reconditioned hundreds of XK engines over the years and have used the same experience and expertise to recondition this XK SP Head for improved performance and reliability. For any other enquiries around the world for our Jaguar XK cylinder heads please contact us with confidence. Call us on 0115 9262266 or email us at info@thorntonrestorations.com.