PONTIAC HEAD DIAGRAM
CASTING NUMBER YEAR & FACTORY APPLICATION CHAMBER VOL# CC’S
6X 75-79 350 & 400 ALL 75-76 455 see table below
5C,5X,5G 75-76 455, SOME 350 93-114+
EDELBROCK PERFORMER RPM ALUMINUM 72 or 87
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Pontiac Heads – Butler Achievement
https://butlerperformance.com › p-34889-pontiac-heads
The 4X head was the 49-state casting used on all ’73-74 400 and 455ci engines. Because Pontiac offered the 400 2-cylinder, 400 4-cylinder with manual and automatic transmissions, and the 455 4-cylinder for 1973 and 1974, separate applications of the 4X head were required to accommodate such wide usage.
Cylinder heads from the 70s can usually be milled up to 0.060 inches without any problems. Every 0.005 inch removed from the deck surface reduces chamber volume by 1cc, effectively increasing compression.
Until ’67, the valves in a stock Pontiac cylinder head were at a 20 degree angle to the piston centerline, after which it was changed to 14 degrees.
< li>Other performance changes.
With a 4.12″ bore and 3.75″ stroke, Pontiac’s 400 had a similar bore and stroke to Chevy’s big-block 396 (even when the Chevy actually 402 cubic inches displaced). p>
The Role of Cylinder Heads
The more air you pump into an engine, the more air/fuel you can burn and the more power you can produce. Building horsepower isn’t quite that simple, but it’s the basic concept. The cylinder head is the main component that intakes air/fuel and expels exhaust gases.
1955-63 blocks have the casting code on the passenger side of the block. For 1964-67 they can be found on the distribution block. Casting codes for 1968-81 appear on the ledge at the rear of the block behind cylinder eight. Once you find the casting code, you can find your block in a number of searchable databases.
One of these tests is to cc’en the heads (cc = cubic centimetres). This is a process where we physically measure the volume of the combustion chamber. This is important as it ensures consistency across all cylinders.
Answer: It depends on the type of cylinder head. When the cylinder head is designed for street applications, larger valves generally do not improve airflow. Often large valves actually reduce airflow.
Larger valve heads may give you more overall torque than a simple cam swap. If your heads have stock valves and you put a larger cam, you’ll have to rev the engine faster to get the same torque and power.