The Lotus 98T was a Formula One racecar designed by Gérard Ducarouge & Martin Ogilvie, and built by Team Lotus. It was made to compete during the 1986 Formula One season, and was a development of the Lotus 97T of 1985. Of the four chassis built, three were assigned to lead driver Ayrton Senna, now in his second year with Team Lotus, and one to team mate 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 sequential Hewland gearbox.

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 test beds would not have a sufficient power rating to measure the 1.5 litre turbos output at above 4 bar boost. It is claimed that the Renault EF15B in its pinnacle increment produced around 1200 HP at unrestricted boost pressure, thus making it one of the most powerful engines ever used in Formula 1 history.

This was however during qualifying, where teams used unrestricted boost pressures for maximum power output, and for very quick lap times. These unrestricted engines were very unreliable, and would only last about a couple clean laps. Therefore, the 98T produced around 900 HP in race trim. The 98T was also the final Lotus powered by a Renault engine, as Lotus switched to Honda for the following year/season.

The gearbox came in two variants, a conventional five speed and a new six speed. The six speed was very much a development gearbox and was largely unreliable. While Senna opted to run only with the five speed, Dumfries was tasked with testing the six speed. Both gearboxes featured Hewland internals within a Lotus designed casing.

...
Wikipedia