When the Formula One regulations changed for 1966 from a 1.5-litre limit to either 3.0 litres normally aspirated or 1.5 litres supercharged, BRM chose to develop a 32-valve, 3.0-litre H16 by effectively doubling up their existing V8. The initial version produced 395 horsepower at 10,250 rpm; a later 64-valve development raised that to 420 hp at 10,500 rpm. While these were reasonable figures relative to the era's V12s and the later Cosworth DFV, the H16 was extraordinarily heavy — 555 lb at introduction, reduced to 398 lb in its final lightweight form — and had an extremely narrow power band.
The engine's complexity was its greatest liability. Each cylinder bank required its own water radiator, fuel metering unit, distributor, and water pump. Crankshaft vibration was persistent, and quick-fix balancing weights developed the habit of detaching and destroying engines from within. Of 40 championship entries, engine, transmission, and related failures caused 27 retirements. Jackie Stewart described it as unnecessarily large, heavier in fuel and oil and water requirements than its rivals, and destructive to vehicle agility.
The same engine was also supplied to Team Lotus, where it powered the Lotus 43 as a stopgap before the Cosworth DFV arrived.
The P83 used a riveted Duralumin monocoque with integral fuel tanks on either side of the driver, consistent with contemporary designs such as the Lotus 33 and Cooper T81. One distinctive feature was the adoption of a stressed-member engine — the H16 was bolted directly to the monocoque as a structural element, a layout that the much more successful Cosworth DFV would later establish as the norm. The gear lever was positioned to the left of the driver. The engine's height forced the entire unit to be raised slightly to accommodate the lower exhaust exits, pushing the car's centre of gravity both rearward and upward compared to rivals.
The P83 appeared for the first time at Monaco in 1966, where Stewart used it in practice before opting for the older P261 for the race. Both Hill and Stewart practiced with the car in Belgium without racing it. The H16 was then set aside for three rounds while development work continued, returning for the last three rounds of the year.
At Monza, Hill's H16 blew on lap one while Stewart suffered a fuel tank leak. The United States Grand Prix at Watkins Glen offered a more promising result: Stewart climbed to third before retiring with a broken cylinder liner, and a lap later the leader Brabham broke a camshaft, leaving Clark's Lotus — also H16-powered — to win, the engine's one and only championship victory. The final race in Mexico saw both cars retire with mechanical problems. Hill and Stewart had stood second and fifth in the championship after six rounds in the P261; they ended the year fifth and seventh without scoring a single point in the P83.
Graham Hill departed at year's end and was replaced by Mike Spence. The 1967 season saw the P83 used more consistently, with Stewart, Spence, and for some rounds Irwin in Reg Parnell Racing's entry, all competing regularly.
The car's best result came at the Belgian Grand Prix at Spa. Stewart inherited the lead when Clark's Lotus encountered problems, then was passed by Dan Gurney after developing a gearbox problem that required him to hold the gear lever in place with one hand. He brought the car home second, more than half a minute clear of third. Spence finished fifth. At the non-championship Oulton Park Spring Cup, Spence delivered his best result in the car with a third place in one heat.
Spence provided the P83's only championship points of 1967, finishing sixth at Monaco — the last car classified and four laps behind winner Denny Hulme — and fifth in Canada and at Monza. Irwin's fifth-place classification at the French Grand Prix added two further points. The team finished sixth in the Constructors' Championship.
The BRM P83 is remembered as one of the more spectacular engineering failures in grand prix history, ranked alongside the BRM Type 15 as a product of overcomplicated thinking. Where BRM's rivals moved toward the elegant simplicity of the Cosworth DFV, BRM committed fully to a layout that was too heavy, too fragile, and too narrow in its power band to be competitive. Stewart left for Ken Tyrrell's operation at season's end; Spence was killed at Indianapolis in May 1968; Irwin's career ended following a crash at the Nürburgring. Three of the chassis were subsequently converted for Formula 5000 use with American and Rover V8 engines.