The Honda engine deal was signed late, in August 1987, forcing a rushed design process for the 1988 car.
Here is the detailed story of the car often designated in engineering studies: 1. Origins and Design Philosophy (1987-1988)
In 1988, F1 was transitioning away from turbos, imposing strict fuel limitations. The MP4/4 was built specifically to work within these constraints.
If you are interested in a different McLaren model (e.g., the MP4-12C road car or the MP4/11), let me know! I can also provide more details on the technical specs of the MP4/4's Honda engine.