A further programme to fit a specially modified, big valve, 6 port cylinder head to the R-Type Continental engine was developed in 1955. This modification was designated OPWAS. The first head was fitted at Crewe by the experimental department. Power at the flywheel was raised to 178 BHP. Further conversions were carried out at the Hythe Road. Additional cylinder head kits were sent to regional service depots. This modification has caused confusion, as the modified engines are sometimes mistakenly identified as S-1 type replacement engines.