The Fully CNC Big Block Chevy JAILBIRD 390 is exactly what happens! With CNC porting to offer superior performance, the JAILBIRD 390 will deliver for larger cubic inch engines of 565-640 allowing aggressive cam profiles to make maximum power. Touting an impressive 467 CFM at .900 lift with professional bowl blending and a competition 6-angle valve job to release its full potential, this is the right head for you! Offered as CNC without bowl blending, the JAILBIRD 390 produces 436 CFM at .700 lift with 4.625” bore fixture and 426 CFM on 4.50” bore fixture. Either way, you cannot go wrong with the JAILBIRD 390! The Jailbird is a perfect choice for Power Header, Nitrous, Super Charger and Boost!