Lotus plans to race its long wheelbase car from the Korean Grand Prix after concluding that it is a step forward over its current version.
Kimi Raikkonen trialled the new car during practice for the Italian GP but the team elected not to race it because it was not convinced enough about the improvements it had delivered.
However, following analysis of the car at the team's Enstone factory since Monza, Lotus engineers are convinced the new car will be a step forward and are now preparing for it to be raced by both Raikkonen and Romain Grosjean from the next race in Korea.
The team decided not to bring it to Singapore because it is optimistic of a decent result this weekend and did not want to compromise its chances by experimenting with a new configuration.
Team principal Eric Boullier told AUTOSPORT: "We should bring it back hopefully for both cars all weekend from Korea - and then even for the rest of the season."
Lotus trackside operations director Alan Permane added that the long-wheelbase car should address deficiencies the team has uncovered in the E21.
"It should give us a more stable car," he told AUTOSPORT. "The main weak point of our car is combined turn-in and braking - and the problem is when we cure it we then have too much mid-corner understeer.
"This [the long wheelbase] should in theory allow us a better window and get us out of that area we're trapped in. It should give us a stable car on braking and turn in, but with a good front end."