Lotus is set to drop its passive drag reduction system for the rest of the Belgian Grand Prix weekend because of a lack of dry running on Friday.
The team had planned to run the device, which is designed to redirect airflow to stall the rear wing at high speed and thereby slash drag, at Spa but has not made sufficient progress with it.
"The passive drag reduction system we have been working on for a while," said Lotus technical director Nick Chester.
"We targeted it for Spa and we ran it through P1 and learned some more with it.
"I don't think we are going to carry on through this weekend with it because we didn't really get enough dry running to get what we wanted in P1."
Even though not running the design is a setback for the team, it is still planning an aggressive upgrade programme for the coming races, including a long-wheelbase car for Monza.
Kimi Raikkonen is currently Sebastian Vettel's closest challenger in the drivers' championship and it is hoped that Lotus will be able to raise its game to allow him to stay in the hunt.
"We are targeting strong development to the end of the year and the long wheelbase for Monza is part of that," Chester said.
"We are going to keep bringing developments through Monza and then the following races as well."
The lengthening of the wheelbase will not require any major changes to the Lotus monocoque and Chester confirmed any necessary homologation work has already been done.
"We wanted to do it because we have seen the performance gains associated with it," said Chester when asked by AUTOSPORT about the wheelbase change.
"The way we are going to do it is with a front suspension change. [Homologation] has already been done."
SAUBER COULD RACE PASSIVE DRS
Sauber also tried its passive DRS design in free practice at Spa, reporting encouraging results.
The Swiss squad has run it previously in testing but its performance today means it is possible it will change its plan not to race with it.
"The system performed better than we expected," said Sauber head of track engineering Tom McCullough.
"We are still not at the stage where we think we are going to race it even though we are pretty tempted at the moment.
"Quite a few engineers are looking at the data and we will make our decision tonight."