What will really help the '05 4200 is to port the exhaust side - it really needs help.
Without porting @ 8-10 PSI you should get 350HP with porting another 25-30 more. The '02 to '05 exhaust ports are really restrictive as cast but there is enough material to do a good port job. The intake just needs a minor clean up to knock off 1 sharp edge, otherwise its good.
Stainless Works is making a header for these engines now.
Last edited by efi-diy; 10/10/09 05:59 PM.
