With the 90° TAG V6 at their disposal and a fuel tank size of 195 litres (down from 220 litres), McLaren proved that the concept did work, with redesigned side pods also getting the treatment (only the nose section remained as a visual reminder of the MP4/2C, though it too was lower and approximately 10% smaller). The improved aerodynamics helped Prost and Stefan Johansson to be closer to the more powerful Honda-powered cars than they might have been with the older MP4/2 design, although the team was hampered by unreliability which had crept into the TAG engines which had been redesigned in 1987 to cope with the lower fuel limit and the FIA's controversial pop-off valve which restricted turbo boost to just 4.0 Bar. The team was able to build on this and, with the smaller 80° Honda V6, and a reduction in fuel tank size from 195 to 150 litres, the sleek-looking MP4/4 was produced and first appeared early in 1988. It was one of the few competing cars that year that was an all-new car; Ferrari, Lotus, Arrows, Tyrrell, and others were using updated or developed versions of their previous years' cars in order to build new cars for the 1989 season when turbocharged engines would be outlawed altogether.