The 861 was built around a carbon fibre and Kevlar composite monocoque. A reduction in the minimum fuel tank size to 195 litres for the 1986 season allowed the overall car to be made smaller, which in turn improved airflow to the rear wing for additional downforce and grip. Despite efforts to reduce weight, the car remained close to but above the 575 kg minimum weight limit. The car appeared in the familiar red and white livery of West cigarettes, which continued as title sponsor.
Suspension was double wishbone at all four corners, operating springs and dampers by pullrods. The season began with conventional steel brakes, but Zakspeed experimented with carbon-carbon brakes from Monaco onward, racing them from the German Grand Prix. Technical director Helmut Barth acknowledged at year's end that the fundamental concept of the chassis, which dated back to 1983, had become outdated, describing it as "too big" and carrying "too much drag."
Zakspeed's own 1.5-litre turbocharged four-cylinder engine, the 1500/4, powered the 861. For 1986 the team adopted a low-pressure Bosch Motronic electronic fuel injection system originally intended for an Alfa Romeo straight-four turbo programme that had been cancelled. This replaced the mechanical injection system used during 1985 and brought improvements in throttle response, drivability, and fuel consumption.
In race trim the engine ran at approximately 3.6 bar of boost, producing around 850 bhp — comparable in output to the championship-winning McLaren MP4/2's TAG-Porsche V6. For qualifying, boost could be raised to around 4.5 bar, yielding approximately 1,000 bhp. These figures placed the Zakspeed engine in the midfield of turbo outputs, well behind the headline BMW-powered cars but sufficient to be competitive against atmospheric machinery. The transmission used an in-house magnesium alloy casing containing modified Hewland DGB internals carried over from the 841.
For 1986, Zakspeed expanded from one car to two. Jonathan Palmer continued in one chassis, and Huub Rothengatter joined in a second car, contributing funding that helped sustain the programme. The arrangement had a downside: running two cars stretched the team's slender resources and limited testing time, hindering the development of the 861.
Ten finishes were recorded across the season by the two drivers. Palmer's best result was an eighth place at the Detroit Grand Prix, matched by Rothengatter's eighth in Austria. Neither result was points-scoring under the contemporary scoring system that awarded points down to sixth place. The team could not afford a test driver, and its reliance on a relatively underfunded development programme meant it consistently ran at the back of the turbo runners.
The 861 chassis were carried into the opening two races of the 1987 season while the new Zakspeed 871 was completed. A single 861 was retained as a spare throughout 1987 and appeared in race conditions at the Detroit Grand Prix, where Martin Brundle used it after crashing his 871 during practice. He retired from that race with turbo failure.
The Zakspeed 861 represents the team's most complete attempt to run a competitive two-car programme with fully in-house machinery. The car was hampered throughout by budget constraints, an outclassed engine package, and an underlying chassis concept that had been stretched beyond its competitive lifespan. Jonathan Palmer's eighth place at Detroit and similar finishes represented the ceiling of what the car could achieve in 1986. The 861 was superseded by the Zakspeed 871 for the bulk of the 1987 campaign, as the team continued its pursuit of competitiveness with progressively refined versions of the same basic formula.