Rover launched the 2300 and 2600 models in late 1977, finally laying to rest the P6 and Triumph 2500 models after their long and distinguished service. As explained before, these inline six cylinder engines were very loosely based on the old Triumph straight six, but with changes to the cylinder heads, new cylinder blocks, crankshafts, carburetion and just about everything else, thereby bringing them up to date. The new models were warmly received by the press, especially the 2600 model, being viewed as a car that could do 95 percent of what the V8 engined model could do, but at a lower cost. Production of the new engines was slow to build up and again BL were left with the situation of not being able to supply the cars that customers wanted. It was not until the spring of 1978 that one could actually obtain a 2300 without wait: that was an unforgivable crime for the company to commit yet again. There was demand for the 2300 and 2600 models and the factory at Solihull was not producing enough to satisfy this demand.

Buyers remained faithful to the 3500 and the range of 2300/2600 started to sell reasonably well, with the 2600 especially doing well on the continent. The second oil crisis of 1979 affected the Rover range along with all other large cars, but sales held-up relatively well and the arrival of the smaller engined cars meant that Rover could change the marketing emphasis of the SD1, pushing the 2300 and 2600 models, making sure that customers were well aware that there was a path for former 3500 buyers to downgrade to.

1979 also brought the first changes to the SD1 range, with the addition of the V8-S model. This was the first attempt by Rover to move the model further upmarket in an attempt to expand the range’s sales potential. The V8-S basically included all options available to the 3500 model as standard, with the addition of such toys as air conditioning and electric sunroof. In effect, this was a test-bed for the North American version of the 3500, which then undergoing preparation work in readiness of its launch the following year. Despite this, sales continued to fall in line with all other large cars due to the global recession that was now biting very hard. The expansion of the range continued into 1980 with the release of the even more lavish Vanden Plas model, to replace the V8-S, offering even more interior opulence – having every possible optional extra included as standard. Further running improvements were made across the range, and the array of models was expanded and build quality was considerably tightened-up