# Pontiac 6X head mystery - is this possible?



## 32sbct (Jul 28, 2016)

So, I picked up two 6x casting code heads with a bunch of other spare parts with my 66 GTO. Here is the strange part. Both heads show a casting date of L226. Which would indicate Dec 22 1976. Both show a day shift indicator. However on the driver side head the vertical boss is stamped 4 indicating a small chamber head. But on the passenger side head the vertical boss is stamped 8 indicating a large chamber head. The previous owner told me they came off the same car. So, my question is this, how do I figure out if these are large or small chamber heads? They look totally identical except one has a GM3 pattern cast on the head and the other has a GM4.

Marty


----------



## Pinion head (Jan 3, 2015)

Very odd, but possible! IF they were mine, & I needed the smaller chamber 6X heads , I'd pick up another 6x-4. Have never ran across the chamber mismatch, and have pulled literally tons of 6x-4's as part of my specialty core business. The oddest things I've come across is one B of '75 dated 5C-4 on one side, one B of '75 dated 6x-4 on the other side. Engine was an early Feb '75 cast 350, & the head gaskets were original GM, as were the freeze plugs.

Odditys...
- Started pulling 455's & 428's in the early '80's, & so far have examined three 455 blocks coded for big cars that were all cast A082, t& each were NOT drilled & tapped for outer main cap bolts. Had that block had ended up being used for a performance 455 HO application, it would have had the outer bolt holes drilled & tapped just like a good 99% of the '70-73 Dport 455 blocks I've examined. Have had tons of '70-73 455 short blocks including nearly two dozen '72 455's & the A082's were the first instance Id ran across of theengine plant skipping the drilling & tapping for ye outer holes. Have also ran across ithis in two June of '73 dated 455 blocks. Just mention this, as at the time, I need a non drilled & tapped 455 block to have it set up with splayed main caps from Program Engineering. i totally blew off tearing down the first A082 dated 455 short block, which was setting @ my shop, and waited several weeks till I found & pulled a '75 dated 455 block. 
-Pulled a Pwh '79 T/A usage 400 4spd short block several years ago out of a '79 GrandAm. The GrandAm had obviously had an engine transplant, & the 6x-4's were gone, replaced by 6x-8's. a little disappointment when I scraped the paint off, & GrandAm ended up selling as a roller.

Up into the early 90's, most traditional Pontiac guys scoffed at the 6X heads, & didn't know about the secondary (stamped) codes. 5C-4's are just as good if looking for a Dport head that an be easily cut to 86cc chambers.


----------



## PontiacJim (Dec 29, 2012)

32sbct said:


> So, I picked up two 6x casting code heads with a bunch of other spare parts with my 66 GTO. Here is the strange part. Both heads show a casting date of L226. Which would indicate Dec 22 1976. Both show a day shift indicator. However on the driver side head the vertical boss is stamped 4 indicating a small chamber head. But on the passenger side head the vertical boss is stamped 8 indicating a large chamber head. The previous owner told me they came off the same car. So, my question is this, how do I figure out if these are large or small chamber heads? They look totally identical except one has a GM3 pattern cast on the head and the other has a GM4.
> 
> Marty


The only way to know would be to CC the chambers. Here is a video: 




You can also bring the heads to an engine shop and they can do it as well.


----------

