This a summary of events where a 1988 Lotus Turbo Esprit was de-tuned whilst fitting a later type Goetze head gasket (Lotus part number B912E7029Z) and replacing a split waste-gate diaphragm. What should have been a routine task turned in to a chase to produce a methodical solution to increase the engine output.
The following background information is applicable to all Turbo Esprit engines (type 910) that were built from 1980 to 1988. These vehicles were fitted with several variants of the 910 engine. From 1980 to early 1982 all Turbo Esprit’s engines were built with a dry-sump lubrication system. This comprised of a compact multi-stage oil pump integrated in to the sump casting. This was driven by a small toothed belt connected to the front crankshaft pulley.
From 1982 onwards, all Esprit’s both normally aspirated and turbo-charged were manufactured with a wet-sump lubrication system. All of these vehicles were fitted with Dellorto carburettors where the turbo charger blew through the entire induction system (including the carburettors)
Lotus also offered two versions of the engine which first comprised of a “standard compression ratio” of 7.5:1 and a maximum boost pressure of 0.55 bar (8.0psi)
Later on in 1985 Lotus upgraded the engine which comprised of the “high compression ratio” of 8.0:1 and a maximum boost pressure of 0.65 bar (9.5psi)
In 1987 Lotus introduced the Turbo Esprit HCi which comprised of the high compression engine but fitted with Bosch K-Jetronic fuel injection (mechanical fuel injection system instead of Dellorto carburettors)
The heart of the HC engine is a stiffer and much stronger cylinder block, Nikosil cylinder liners, Mahl forged pistons, a new HC cylinder head with larger ports and superior gas-flow provided by an improved inlet manifold.
It is interesting to note that Lotus changed compression ratios with the aid of different pistons and the subsequent bowl volume contained within the crown.
These turbo-charged engines were normally fitted with a thin laminated head gasket that determined the final compression ratio. In January 1993, Lotus introduced a new composite head gasket that was much thicker and dropped the overall compression ratio typically by 0.5.
See part two of this customer case study where the detailed analysis of waste gate dimensions and operation are discussed.