What are "555" heads?

[big66440]

Sorry to sound so ignorant,I've read quite a few threads on this forum of people mentioning "555" heads I'm assuming thats the last 3 numbers of the head castings but why are they so sought after,and what makes them so popular?

[George]

They are the '55 331 Chr heads. Those & the 56 354 are considered the best flowing. The 55 heads have 3 5s in the casting number(non consecutive), & are the only ones that do.

[big66440]

Cool,I have a pair of 56' 354 heads,do you know if all the 354 heads for that year fall under the "best flowing" category?

[johnny5]

Cool,I have a pair of 56' 354 heads,do you know if all the 354 heads for that year fall under the "best flowing" category?

The ports in the 1954-1956 passenger Chrysler car and industrial heads are the same, so yes.

[oldngood]

Cool,I have a pair of 56' 354 heads,do you know if all the 354 heads for that year fall under the "best flowing" category?

'56 is better than '51-'53 heads, and marginally better than '57-'58 heads.

If you had the choice and all were easily obtainable, one would choose the '555" for value.

If you have '56 heads, just run those. Any '54-'56 head will work and have the big ports, but each has little differences like water jackets, dowel pins, etc.

[dan miller]

The 1954 and 1955 heads are the best, the only difference being the water outlets. The 1956 are just a tick less desirable.

Be careful with industrial heads. Not all have the large ports and valves. Many of the late industrial engines come with passenger car heads (on Windsor blocks), and hydraulic lifters.

Danny