The Porsche board objected as this engine would give rise to a rumour of a new 911 with a front-mounted Volkswagen-based engine, but also it is theorized that the board wanted to maintain some distance from the Volkswagen group. Ferdinand Piëch proposed the use of a 4.6-litre 90 degree V10 engine with 88 mm bore spacing, a derivative of the Audi 5 cylinder engine (used to power the Lamborghini Gallardo), which in turn is based upon the Volkswagen EA827 unit. Porsche engineers wanted a large-displacement engine to power the 928, and prototype units were built with a 5-litre V8 engine rated at 300 PS (220 kW 300 hp).

After deciding that the mid-engine layout did not allow enough room in the passenger compartment, a front-engine, rear-wheel drive layout was chosen. Having the engine, transmission, catalytic converter(s) and exhaust all cramped into a small rear engine bay made emission and noise control difficult which were the problems Porsche had with the 911. Several drivetrain layouts were considered during early development, including rear- and mid-engine, but most were dismissed because of technical and legislative difficulties. Ordered by Ferdinand Porsche to design a production-feasible concept for the new model, Fuhrmann initiated a design study in 1971, eventually yielding the 928 which was the first clean sheet design by the company for its own model the 356 was a similar design to the Volkswagen Beetle, the 911 was an evolution of the 356, the 914 was a joint effort intended as a replacement for the Volkswagen Karmann Ghia and 912, and the 924 was the result of abandoned project by Volkswagen and Audi. The targets were that the car had to compete on par with offerings from Mercedes-Benz and BMW while also being successful in the United States, Porsche's main market at the time. This would set it apart from the 911, with its relatively spartan interior and true sports car performance. Fuhrmann envisioned the new range-topping grand tourer model as being the best possible combination of a sports coupé and a luxury sedan. Slumping sales of the 911 in the mid-1970s seemed to confirm that the model was approaching the end of its economic life cycle. Fuhrmann believed that the future of the company relied upon grand touring cars with conventional engines rather than unconventional sports cars.

Managing director Ernst Fuhrmann was pressuring Ferdinand to approve development of the new model due to concerns that the then-current flagship model, the 911, was reaching the limits of its potential. In the wake of the 1970s oil crisis, executives, including owner Ferdinand Porsche, were beginning to consider adding a more fuel-efficient luxury touring car to the line-up. By the late 1960s, Porsche had firmly established itself as a manufacturer of high-performance sports cars.

4.7 engine exploded view