Additional fuel tanks were added either side of the cockpit to allow the car to run a full Grand Prix distance, and the rear end of the car was cut away to accommodate a 2.0 litre BRM type 56-2 V8, an enlarged and updated version of the engine with which Graham Hill had won the World Championship in 1962.

The car made its debut in the 1967 Race of Champions at Brands Hatch, showing promise with fourth and sixth places in the heats before a missed gear by McLaren in the final race put him out with engine failure.

The M4B's Grand Prix debut came at Monaco,[3] where its short wheelbase made it surprisingly competitive.

At the next event, the Dutch Grand Prix,[4] Bruce McLaren finished 14th in qualifying.

The car was later repaired, but caught fire during a test at Goodwood and was written off.