Pontiac Head Numbers
Compression can be increased or deceased through
proper cylinder head selection. It becomes imperative then to know how
to identify Pontiac heads in order to pick the right one for your engine.
There are D-port heads and round port heads. That characteristic difference
is apparent by looking at the exhaust port openings. If you stumble across
a round port head, you've got something very special. Most Pontiac heads are
D-ports. Very few are round ports and those are automatically considered
Another thing to look at when examining a head
is to see if the head has pressed in studs or is equipped with screw in studs.
Generally, Pontiac heads that are considered high performance will have screw in studs and push rod guide plates. There are many D-port heads, some have screw in studs some do not. Any D-port
head having pressed in studs may be improved to accept screw in studs.
Any quality machine shop can perform the service for you, so keep that
in mind. Most importantly, all D-port heads can be ported to provide increased
air flow. Air flow is one of the keys to making more power in any combustion
engine. Improved air flow will make a difference on your Pontiac engine.
The degree of porting depends on the vehicle's intended use. There is no ideal air flow that will work on all engines.
Every Pontiac head has a casting number on the head. Some have a long string of numbers, some have 2 or 3 numbers, and yet others(low compression, large chambered from the '70s) are alphanumeric, a number
or two and a letter cast into the head. With few exceptions, most casting
identifiers are on the two center exhaust ports. Many Pontiac engines are seemingly missing the casting numbers on the two center exhaust ports. Generally the owners are not removing them, but
the disappearance is attributed to age and rust.
A casting date is also important to locate. The
head casting date is usually found on the exhaust side of the head just
below the valve cover rail. If you must, scrape away some of the grime
to find the information. A letter is usually followed by three numbers.
The letter stands for the month. A=January, B=February and so on. Keep
in mind that the month of the year may fall into the next year's production.
The numbers that follow the letter is the day of the month. The last number
is the calendar year. For example: A109 is probably a casing from January
10, 1969; a head casting with E248 is a casting from 1968 or 1978. If the
casting identifier on the center exhaust ports is visible and it's alphanumeric
(e.g. 6x) then it's from 1978. If there are two numbers, say 16, or 62
or 48, it's a 1968 casting. The casting date and the casting identifier
are critical to identifying a Pontiac head.
There's also information cast on the head that appears like a clock face with a triangle
pointing to one of the 12 positions. There is also "GM" and letters following that which indicate the foundry where the head was cast. This information, however, is not relevant to identifying a head.
Okay, so you've spotted the casting number and the casting date. Unless you've done a lot of study
and logged the info you've found, you still don't know what you've got.
Perhaps the bible that most people look to is Pete McCarthy's book entitled "Pontiac
Musclecar Performance 1955-1979." The book is a cornucopia of information.
There are other sources out there too.
One other thing...never rely on the purported
chamber size of any Pontiac head. Too much time has passed. Many heads
have been milled and the chamber size altered. The best way to know chamber
size is to measure their volume (CC the heads).
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