[mgarblik]

Originally Posted by 73T/A

I mentioned the 3/8 rocker studs and such that were on the heads.In retrospect the 3/8 rocker studs aren’t much of a indicator in how the heads were used in the past do to the fact that they can be changed and swapped out with 7/16 versions in minutes.Do to the fact the heads were 31 years old when I acquired them it’s anybody’s guess.

You mentioned that the 197 heads with a date code of Dec 1970/Jan 1971 would not be used for testing etc due to lead time for the 1973 SD-455 head.It seams plausible to me that there would be enough time .Not necessarily my heads but heads with that date code in general.I never heard that the SD-455 program was turned over to production in the Dec 1970/Jan 1971 time frame.Are you referring to casting the cylinder heads.I have seen a SD-455 head dates of Oct 1972 and some with no dates stamped on them those are probably earlier yet.Im sure the SD-455 guys know.

You are so right about some of the mysteries that surround these engines. My early 73 SD-455 engine has NO casting numbers on the exhaust ports and NO date codes. Only the full part number on each head. It has "A" connecting rods in it so I feel safe saying it was a pretty early engine.

[johnta1]

Here's a sheet that SDBob has explaining the dyno tests they did back in 1971.

[73T/A]

Originally Posted by johnta1

Here's a sheet that SDBob has explaining the dyno tests they did back in 1971.

That’s very interesting.I never seen that one.👍

[73T/A]

Originally Posted by mgarblik

You are so right about some of the mysteries that surround these engines. My early 73 SD-455 engine has NO casting numbers on the exhaust ports and NO date codes. Only the full part number on each head. It has "A" connecting rods in it so I feel safe saying it was a pretty early engine.

The 455-SD is definitely a unique engine.Even though it was produced in low numbers it’s a wonder that it even made it into production with upper management at Pontiac changing attitude toward performance and the federal regulations on the horizon.No other mfg had anything like it at the time.