4x heads ok?
 

I've got a fresh 400 in my 67 lamnes with 4x heads. I'm thinking of getting them ported for a little extra umph. The guy I got the car from said that 6x heads are soo much better.. What should I expect to gain with the 6x's over ported 4x's? It has a mild cam , quadrajet and 3" pypes.
Thanks in advance,
Bill

here we go again......... hang on.
 

Depending on the stamping on the machined pad. The 4X and 6X are the same port design. Some 4X's do have humps in the exh port, but you can grind them out.

My set of 4Xs were easy to Tall-Port.

Intake Runner floor & sidewalls barely needed touching, while I went at the pushrod buldge anyway. Seemed to be plenty of iron at the Bulge to work with.

Intake roof grinds into the tall-port well.

A 4X table
http://fiedlerh.home.att.net/4xheads.htm

Nice table....ready to accept 5C data :)

Sorry I'm so late. The sight crashed right after the post and I'm working too much overtime...250 hrs this year. Thanks for the info. I'll get the casting # Sunday and decide.
Again I thank you all,
Bill

What P dude says is quite true they are nearly identical stock. Ported will be no difference either. Some pontiac "expert" tried to tell me the 6x was the best head period! Same guy thought I was nuts using a set of 1969 #46 heads too. Truth is most D ports can be ported to the same level of performance. I have a set of 6x-8's and a set of 4x-7's. Both sets stock and virtually identical maybe I'll use them some day if I need lower compression.