Brainz

Cars that run in the IndyCar series currently use a normally aspirated (non-turbocharged) 3.5 liter V8 engine built by Ilmor Engineering but branded as a Honda.  The motors make approximately 600 horsepower and have proven to be very reliable; since the series began using these engines in 2007, not a single engine has failed in competition.

In 2012, the IndyCar series will revise the engine rules substantially.  Engine size will be limited to a maximum of six cylinders, with a displacement not to exceed 2.4 liters.  Turbocharging will be allowed, so cars will make the same (or more) horsepower than they do today.

Source: RideLust

http://www.ridelust.com/indycar-engine-formula-revised-for-2012/