[Neale]

Im no expert but here's what Wikipedia says


The TC six-cylinder models had twin 5" headlights which distinguished them from the four-cylinder cars which had single 7" sealed beam headlights on each side. To hold the larger engines, the chassis had reinforced side rails and centre pillar, and a tubular crossmember support under the transmission. In addition, the firewall panels were shaped to accommodate the longer engines and wider bell housing, and were manufactured from thicker metal. This change was spread across the Cortina range so that the four-cylinder models benefited too. But this was not enough to prevent the additional front mass of the larger engines causing roll steer, resulting in relatively unsophisticated handling by today's standards, especially on rough roads. Braking was also an issue under harsh conditions.

Both the TC and TD six-cylinder models were immediately recognised over the four-cylinder versions by the raised 'power bulge' in the center of the bonnet. Basic transmission for the six-cylinder model was originally a three-speed manual floor shift, with a four-speed Borg-Warner single rail transmission available, taken straight from the Falcon GT. Also available was a Borg-Warner M35 three-speed automatic across all models. From 1976 the six-cylinder engines featured a revised crossflow cylinder head, keeping in line with the Falcon.