[Don66GTO]

I have a 66 GTO with a 74 455 from a LeMans with an engine code of YU it also had what appeared to be the numbers 078400 located on the front passenger side of the block. I was wondering if the 4x heads that are on it (the exhaust manifold had 4x stamped into it si I think that it it has 4x heads) are worth the money it would take to get them ported and polished or it I should go in another direction with them.

also do these heads have the d port?

can you get performance heads with the d port or do you have to get the ram air III or IV type heads for making more HP?

I am new to the scene having just purchaced the GTO recently.

[scott cedergren]

I would suggest that you talk to dave at sd performance about some 6X heads. He can cnc port them to get some serious power. He is a really nice guy to talk to and will help you find what you want.

[gtofreek]

The 4X heads are D-port heads. You can get a set of Kaufman[KRE] D-Port heads that out of the box with a good valve job will flow as much as ported 4X's will. They have a better combustion chamber also and will make better power. To have the 4X's ported for decent flow and new valves, springs, retainers, keepers, etc. you will have almost as much money in them and they won't work as good. Just my opinion. Dave at SD performance is good also and I believe he has a CNC program for porting the KRE D-port head also.

[Will]

Since your new to the scene it sounds like you could use a little bit more info about identifying heads, just so you can be sure what you're really looking at.

Here is a pic that will show you where the relevant numbers are on Pontiac heads. Other numbers on the heads than what are circled in this pic don't mean anything as far as identification goes. As you can see, this is a 6X head.



Not all heads have the secondary stamping. To the best of my knowledge, heads that have a secondary stamping due to various chamber and/or valve sizes used with the same basic casting are 4X, 5C, and 6X. Again, this is a picture of a 6X-4 head because it has a '4' as the secondary stamping. The 6X-4 variety had a smaller combustion chamber than the 6X-8 or the rare 6X-6.

Finally, all Pontiac factory heads are D-port except '68 RAII , '69 - '70 RAIV, '71 - '72 455HO, and '73 - '74 455SD.

Hope that helps and welcome to the Pontiac hobby!

[Don66GTO]

Thank you guys for answering. The heads are definately 4x (the photo helped me to make sure of it.) and I will try to contact Dave at SD soon.

[OINK 1]

If they have screw in rocker studs, then cc them. They could be good ones.

Pontiac Gregg