The Lotus 98T was a Formula One car designed by Gérard Ducarouge and Martin Ogilvie and built by Team Lotus for use in the 1986 Formula One World Championship. Development of the previous year's 97T, the car was raced by Brazilian Ayrton Senna, in his second year with the team, and Scottish newcomer Johnny Dumfries.

The chassis featured a lower monocoque than the 97T as a result of a regulation change stipulating a reduction in fuel capacity to 195 litres. The powertrain consisted of the new Renault EF15B turbocharged V6 engine, driving through a six-speed, manual transmission by Hewland.

The EF15B was to appear in two forms, the standard engine and the D.P. engine which featured pneumatic valve springs for the first time. At the end of the season Renault introduced the revised EF15C which in addition to the D.P. valve gear also boasted common rail fuel injection and much-revised water cooling through the cylinder head reducing the likelihood of pre-ignition (detonation). Power figures for this period of F1 history are largely speculative as most engine manufactures freely admitted that their testbeds would not have a sufficient power rating to measure the 1.5-litre turbo's output at above 4-bar boost. It is claimed that the Renault EF15B in its pinnacle increment was claimed to produce in excess of 1000 HP at unrestricted boost pressure, thus making it one of the most powerful engines ever used in Formula 1 histor