Following the demise of Group 7 racing in England McLaren decided to build a car for the new 1600cc F2 class. The Robin Herd designed M4A F2 car was announced in February 1967 and was to be built by Lambretta-Trojan. While the M4A was built for Formula 2, the M4B was the Trojan production car for American Formula B racing.

In total, twenty five M4 cars were built in 1967 and 1968. The M4A/B was built from comparatively simple constant diameter bathtub monocoque, formed from aluminum paneling which was bonded and riveted to four steel bulkheads. The M4A/B's suspension is double wishbones located by long radius arms front and rear with conventional outboard springs. Fuel is carried in two 10 gallon tanks on either side of the cockpit with a further 5 gallons in a seat back tank. The lower body is formed by the Monocoque, the nose and the cockpit surround being fiberglass. The car ran on McLaren Elva cast magnesium wheels, thirteen inch high with seven inch wide rims at the front and ten inch rims at the rear. The M4B is an extremely light car weighing jut over the F2 minimum weight.

One of the M4As was developed for Bruce McLaren to race as an interim Formula 1 car ad this was also given the M4B title. McLaren used his M4B between the demise of the M2B and the appearance of the new BRM powered M5. The F1 McLaren M4B was a modified production car, the rear end cut away to hold a RM 2.1 litre V8 which could give about 280 bhp. It also ran with additional fuel tanks prominent on its sides to provide for the GP distance range. Bruce debuted the M4B at the Brands Hatch Race of Champions, where he competed well in Heat 1, but in Heat 2 he missed a gear, over revved and blew up the engine. In total, Bruce drove the F1 M4B in five races with his best finish in the Monaco GP on the 7th May 1967. The M4B's size meant it was exceptional at taking on the winding street circuit course of Monte Carlo, but during the course of the race its battery ran flat and the resulting pit stop for a new one meant he fell from a possible second place to fourth. Bruce went on to crash the M4B at the Dutch GP and then, while testing the repaired car at Goodwood in England, the car caught fire and was totally destroyed.

The M4B in the Mathews Collection is one of the Trojan production cars and was originally raced by American Chuck Dietrich. In 1968 Dietrich won seven races in this car, five in Formula , and two in SCCA GP Formula races.