Lotus Renault GP technical director James Allison (LEFT) says Renault's radical forward-facing exhaust concept has hurt the squad in 2011, with the design proving troublesome on slow-speed circuits and also difficult to develop.
Allison said the concept had "entombed" the team, as it had not proven as successful as first hoped at the start of the season.
Renault tried a more traditional rearward-facing exhaust layout in Germany and Hungary, but the switch caused problems of its own and forced a return to the original, radical design which Allison says still hurts the team's performance.
"At the point when I made the decision about the forward exhaust system, it was a very exciting concept and one which was outperforming our rearward blown system," Allison said. "It looked like it had a lot of potential to deliver really race-winning performances. I think that two or three things have held us back since then.
"The first is that it has proved really difficult to develop it. We came out of the box reasonably well, but it has been much harder to add performance than we might have liked.
"The second is that it's quite tricky – it all has to be ever so nicely looked after in order to generate the downforce that it is supposed to generate and at several circuits we see a shortfall of downforce compared to what we would expect."
Allison explained that the exhaust woes were amplified on slow circuits like Singapore, and said that detracted from a number of upgrades they had brought to the car in recent races.
"We came [to Singapore] with a mixture...we had a bit of trepidation, but also a small amount of cautious optimism because there is no doubt that we have put a lot of performance on our car in the last few races.
"We hoped that that would take the edge off what has been utterly apparent this year at Monaco, Hungary and now Singapore that at any track where we have a preponderance of low-speed traction events, we struggle.
"We honestly didn't foresee the difficulty that we get in the 60-100kph (37-62mph) corner ranges. That's quite a slow corner – and what you get in those corners, we are not actually able to mimic in the wind tunnel."
Allison predicted that the remaining five races would suit Renault better, but said the team would have to wait until next year to finally correct the exhaust design.
"The majority of the circuits that are remaining, we should be OK at. We will hopefully be a bit more credible in the remaining circuits.
"We have been working on next year's car back in January and we have had a lot of people working on it for quite a long time and we're pretty much all working on it now. There is a lot of work being put in. Next year is reset to a more conventional setup and we'll go from there."