[steve25]

Pontiac engineering U.P.C codes tell the progression of engine development and the time span of usage in many cases.

The code only changed when significant changes were done for the most part.

A few brief examples.

L-74. All high comp 400 4bbl medium performance motors from 68 to 70.

L-78 all low comp 400 4 bbl medium performance motors from 1971 to 1979.

L-67 1968, RA1 D port, RAII round port, so where into the round port era now.

L-67 1969 and 70, RA4 motors except in the F body .
These RA4 engines in 1970 got a LS-1 code

L-75 base line 455 engines.

LS-5 1971-72 455 round port HO.

LS-2 455SD.

So the 455SD was in development as early as 1971

The LS-2 U.P.C code is to me the most likely reason for all the number 2 stamping on your heads there.

Note that once engineering got to making a 455SD 16 preproduction casting that they put the air injection boss back in across the top of the exh ports in case they needed to add a air pump to meet emissions.

Here are molds of an Intake and Exh port from a non ported 455SD production head.

[73T/A]

Originally Posted by steve25

Pontiac engineering U.P.C codes tell the progression of engine development and the time span of usage in many cases.

The code only changed when significant changes were done for the most part.

A few brief examples.

L-74. All high comp 400 4bbl medium performance motors from 68 to 70.

L-78 all low comp 400 4 bbl medium performance motors from 1971 to 1979.

L-67 1968, RA1 D port, RAII round port, so where into the round port era now.

L-67 1969 and 70, RA4 motors except in the F body .
These RA4 engines in 1970 got a LS-1 code

L-75 base line 455 engines.

LS-5 1971-72 455 round port HO.

LS-2 455SD.

So the 455SD was in development as early as 1971

The LS-2 U.P.C code is to me the most likely reason for all the number 2 stamping on your heads there.

Note that once engineering got to making a 455SD 16 preproduction casting that they put the air injection boss back in across the top of the exh ports in case they needed to add a air pump to meet emissions.

Here are molds of an Intake and Exh port from a non ported 455SD production head.

Thanks for the detailed info on the various UPC head codes.On a update I mentioned that I located four number 1’s on the other cylinder head.They are configured just like the number 2’s on the other head.Gor some reason somebody wanted them individually identified.But both heads do have the RUSS stamping with 10750 stamping below.

[unruhjonny]

Originally Posted by steve25

Pontiac engineering U.P.C codes tell the progression of engine development and the time span of usage in many cases.

The code only changed when significant changes were done for the most part.

A few brief examples.

(removed)

LS-5 1971-72 455 round port HO.

LS-2 455SD.

...

my understanding is that RPO/UPC codes were reused, and issued by the parent company - not necessarily a divisional thing;
As an example a 1969 Chevelle could have been ordered with an L78, and so could a same year GTO;
In the case of the GTO it was the ‘base’ 400/4bbl engine - for the Chevelle it was much more special.

Here is my correction of the engine codes which Pontiac used, and what I removed from above:

L-30: 350/2bb 1968-1977

L-65: 350HO 1968/69; 350/4bbl 1974-1977; best 350 you could get for the given year

L-67: 400 ‘Ram Air’; 1967-1968.5 ‘D-port’; 1968.5-1970 ‘round-port’; the best 400 you could get for the given year

L-74: 400HO 1967-1969(?); “RAIII” 1969-1970; one step down from the L-67

L-75: 455/4bbl 1970-1976; “bread and butter” 455 performance engine for which ever model year

L-78: 400/4bbl 1967-1979; “bread and butter” 400 performance engine for which ever model year

LS1; (purported) RAIV-SD 1970; did not pass pre-production stage.