HP - when was it used and why?

I am looking for information on the "HP" or "HP2" stampings, which are, for example, found on the front pad of the 383 in the pic below.

Information I have found from reliable sources is listed below, (reliable sources include the Barracuda Data Book, Galen books, and information I have received directly from Chrysler, including my IBM build card, a letter, and other documents):

- For all 1967 and older engines (including Lo Performance 1968 engines), you have to date the engine prior to the scheduled production date of the vehicle.

- For all 1969 and newer engines (including Hi Performance 1968 engines), a (full or) partial serial number is stamped on the engine block.

- All 1968 HP V8 engines are stamped on the top rear of the block near the oil sending unit.

- Engine numbers without the following symbols indicate "standard cylinders and crankshaft bearings".
HP = High performance (includes all 1967-78 440's w/HP2)

- I have also received a letter from Chrysler with my build card, and the letter includes:
H = 383-4 HP 8-Cylinder

-The data book for 67-69 Barracudas also lists the 383 multiple times as 383 HP, never without the HP.

Note: The information above groups all 67 engines with all 68 Lo Performance engines, which could be interpreted as the HP was not available in 67, but the data book lists it for all years 67-69.


Does anyone know when the HP stamping began?

On what engines?

In what models?

Did you have to (or could you) specify an HP engine, and if so was there a corresponding code?

What does the HP stamped on the engine stand for, Hi Performance or High Performance? And is there a difference, (I've seen it listed both ways).

Was HP ever stamped on the heads?

What is the difference between HP and HP2? And was there an HP3?

Why would Chrysler list my engine as 383-4 HP if there is no HP stamped on the block? (definitely the original block)


I've done some research on this, and found a few variations of the 'facts' to where I could answer most of the questions, but nothing definitive.
It seems everyone has their own version of what the reality was, and some appear to be just wrong.

Any help would be appreciated, something concrete to refer to would be great.