4.6 heads on a '03 Crown Vic

On pre '03 Vic 4.6 were the heads different? I think that my wifes '04 Vic has different heads giving more power and on my '03 Vic motor was replaced with an older 4.6 with smaller heads? The Power is consideralbly different. thanks

The 4.6 has non-PI heads until 99, when the PI heads were developed. They offer a smaller combustion chamber than the NPI, but had a larger piston dish. Changes were made again in the 05s.

Putting the PI heads on the NPI engines WITHOUT changing the pistons will boost the compression ratio to about 10.4:1 necessitating 93 octane fuel. Some people will grind down the air dam in the chamber by the intake valve and spark plug ,and reduce the compression ratio. The flow is great, the power does increase, but not as much as higher compression.

I don't know if the 03s or 04s were part of the head changes. It is a possibility. Giving her more power.

04 the air box ,maf sensor and zip tube changed from a smaller size.this could be the reason i dont think the heads changed from 03 to 04.

Sorry I never got back on this one sooner. The 04 does have a larger zip tube and better flowing maf than the 03. Since we can no longer get Marauder maf and zip tubes, every one has advised to get the 04 set up instead. Talk about a kick in the pants difference that you can feel.