Regarding the Scuderi engine - I smell a scam. That engine supposedly compresses air using only one stage, to a pressure of 1885 psig or so. This compressed air can then supposedly go into a storage tank for re-use, or be directly injected into the combustion cylinder.
http://www.sae.org/mags/aei/POWER/7803
One problem with this idea is that this compressed air will reach a temperature of at least 1700 F, which will make any metal air cylinder glow cherry red after a while. Another problem I see is that this heated air will pretty much cause autoignition of any current fuel the moment it is injected into the airstream.