The debate with the new Indycar might have found the answer to the speed question, or the lack there of. The Airbox, or the the hole-ish thing above the drivers head directly behind the cockpit, is a system used by Indycar to help with the exhaust system of the engine. What it also does is slow down the Indycar. This was essential for the old car because if it had not been there, those cars would have been blistering fast. No airbox would result in a faster car. And there are other ways to help aid the exhaust system, and I am sure Dallara is working out those new methods. So many people are starting to wonder if should even exist on the horrendously slow DW12. What the car would look like would be similar to the champ car. See the photos below.
Notice above Pippa's head at the 2011 Indy 500, that is the Airbox.
This is Alex Tagliani's Champ Car in Surfers Paradise in