Chrysler's 5.7-liter Hemi is the standard fitment, and with 380 horsepower and 403 pound-feet of torque, it makes a good argument. Alternatively, 6.1 liters of SRT crate Hemi will give you about 450 hp, and then there's the 426 cubic inch version of the SRT engine, which Mr. Norm's modified with forged internals and more stroke. Thus tweaked, the 426 nets you about 600 hp, nearly triple the 225 hp kicked out by the police-spec 360 in the original.
http://www.autoblog.com/2009/03/19/dodges-iconic-lil-red-express-to-ride-again-thanks-to-mr-norm/
http://www.autoblog.com/2009/03/19/dodges-iconic-lil-red-express-to-ride-again-thanks-to-mr-norm/