Reworking the existing AEC AV760 engine into the turbocharged TL12 accounted for a large part of the Marathon’s development costs. The TL12 had the same bore and stroke dimensions as the AV760 but, following extensive development under AEC’s engine design team led by Keith Roberts, it was launched as a new power unit. The aim of the development programme was to produce a turbocharged engine with top reliability, long service life and sound environmental credentials.
While the naturally-aspirated AV760 typically produced 206bhp net at 2000rpm and 585lb.ft of torque
