Going to refresh top ends of 2003 500 EFIs myself and would like some input on all parts and things that need to be done. What is the latest and greatest parts for the job. Thinking I need springs, retainers, seals, head bolts, head and exhaust gaskets. Am i missing something and whats the best parts for the buck. Should i take heads to be machined? Motors have 290hrs, compression test was ok but leak down was border line. Thanks

I am getting ready to do this exact thing on my 500 efi. Im using Isky 8005A springs, 10° retainers and locks and fel-pro gaskets. Make sure that you get intake and distributor gaskets. I'm also taking .0020ths off to bump my compression a tad

Ateco sells a top end kit for those engines, new heads, cam, lifters, pcm reflash that claims 125hp increase. Something to think about if parts are damaged. Randy

Randy,
Have you had any work done by Ateco or used any of there upgrades ?

Having some work done now.

i would put new lifters in for shure. i had one blow apart on me befor i got to my top ends and coused me to have to do a full rebuild on the one motor.

formula, what did you end up replacing. End of season and going to do the same?