Chevrolet Big Block Heads – Casting Numbers and Specifications

Chevrolet Big Block Logo

Chevrolet Big Block Heads

Chevrolet Big Block Heads were offered in many different variations within their 51 years of production. GM Production of the Chevy Big Block engine began in 1958 with the Mark I W Series and ended with the Gen VII in 2009.  However, in the aftermarket production of heads, blocks or complete engines continue till this day.

Over the years depending on the application Chevrolet used different head configurations for the Big Blocks. GM installed these engines on grocery getters, high-performance street machines, all-out race cars, trucks, boats, and also industrial applications. To accommodate all these applications the heads were designed with different combustion chambers, valve sizes, and port dimensions. They also produced heads in cast iron or in aluminum to achieve different power output and performance.


Chevrolet Big Block Heads Combustion chamber types

All early Chevy Big-Blocks used closed chambered heads. In 1969 Chevy changed to the more efficient open chamber design.

Closed Chamber Head Combustion Chamber Design

Closed Chamber Head Combustion Chamber Design

Closed Chamber.

The Closed Chamber heads have a smaller combustion chamber. The Chamber is flat and only has a recess cast around the Valves and the spark plug hole. The flat part creates a quench and squish area in between the piston and the head as the piston reaches top dead center. This helps create turbulence pushing the air-fuel mixture to the spark plug.

These heads have a lower combustion chamber volume usually below 100c. Engines with Closed Chamber heads usually use flat top pistons and give a higher compression ratio. However, the compression ratio can be reduced by using a dished piston. They’re not as efficient for emissions purposes as Open Chambers Heads. However, when set up properly Engines with Closed Chamber Heads can provide great low and midrange power.

Open Chamber Head Combustion Chamber Design

Open Chamber Head Combustion Chamber Design

Open Chamber.

The Big Block Chevy Open Chamber Heads have a larger combustion chamber compared to the Closed Chamber design. These types of heads have a round pocket cast int to the head just about the size of the cylinder diameter. This design moves the combustion chamber further up into the head and helped increase airflow at higher RPM.

Chevrolet change to the Open Chamber head design in the late 60s to improve combustion for emission purposes and also lower compression ratios. However, a domed piston can be used to increase the compression with this type of head.

Most engine builders prefer using open chamber heads due to the increased flow at higher RPM. Most aftermarket performance heads use this design.



Chevrolet Big Block Heads Intake Port Types.

All Chevy Big Block Heads came in 3 different intake port configurations. The Large Oval Port, the rectangular port, or the Small Oval Port aka Peanut Port. Early engines used either the large oval port or the rectangular ports heads. The oval port heads were used for the standard output engines in cars, trucks, and boats. The rectangular ports heads were used for high-output performance engines.

In the 90s on the redesigned Gen V Big Blocks, a small oval Port(Peanut Port) was introduced for use on Truck applications. These heads produce more torque at lower RPMs.

Big Block Chevrolet Intake Port Types

Big Block Chevrolet Intake Port Types

Chevrolet Big Block Heads With Rectangular Intake Ports

Chevrolet Big Block Heads With Rectangular Intake Ports

Rectangular Port.

The Chevy Big Block’s Performance Heads have very large Intake runners with rectangular-shaped ports. The intake ports are just about 2 ¾” tall and 1 ¾” wide. Chevy only installed these heads on their high-output performance engines. The heads were used on Corvettes, Chevelles, and other special applications.

These are the heads you want when building an all-out race engine that constantly runs at wide-open throttle. The large runners flow best from 4000 rpm to redline. However, these larger ports don’t generate good air velocity below 4000 rpm and don’t perform as well as the large oval port heads at lower rpm.


Chevrolet Big Block Heads With Oval Intake Ports

Chevrolet Big Block Heads With Oval Intake Ports

Large Oval Ports.

The large oval port type is the most common Chevy Big Block Head. These heads have large oval-shaped ports that are about 2” tall and 1 ¾” wide. These heads work well across the full rpm range. The port is ½ shorter than the rectangular port which helps generate air velocity at lower rpm. With some porting work and larger valves, these are the heads that may be the best choice for a high-performance street engine.


Chevrolet Big Block Heads With Small Oval Intake Ports

Chevrolet Big Block Heads With Small Oval Intake Ports

Small Oval Ports(Peanut Port) Heads.

The Peanut Port heads were introduced on the Gen V big blocks and were designed for truck applications. The ports are 1.56” tall and 1.44” wide. The smaller runner was designed to increased flow at lower rpm to help increase low rpm power and torque.

These heads are not recommended for high revving performance applications. However, they can work well for low revving high torque applications such as pick-ups, tow vehicles, or rock crawlers.


Choosing a performance head for your Chevrolet Big Block.

If you are building a Big Block and need to purchase heads it’s important to talk with your engine builder to come up with the best possible combination for your build. There are many aftermarket heads to choose from. However, if you want to use OE heads the large oval port types are easier to find due to the sizeable production run of the Chevy big-block. The high-performance rectangular port and factory aluminum heads are harder to find and can get costly to purchase.

If your building a full race engine for the drag strip or oval track which will be always be running at high RPM the rectangular heads may be what you are looking for. However, with some porting work and larger valves, the large oval port can perform just as well as the rectangular port heads. Actually, some bulders now prefer the oval over the rectangular port.

There has been many dyno and flow test done over the years to compare the 2 types of heads. The consensus is that with proper porting the oval port heads can flow just a well at above 4000 RPM as the rectangular without losing the middle and lower-end performance.

Building a road course or street and strip engine then the oval port may be the way to go. Remember the old saying that bigger is not always better. The oval port will provide great power and torque and have the good drivability that is needed for these applications.


Casting Numbers to look For.

Oval Port

Casting No.  336781  Mark IV, oval port, open chamber with 120cc.

Casting No.  353049  Mark IV, oval port, open chamber with 120cc

Casting No.  3964291  Mark IV, LS6. rectangular port, open chamber with 108cc

Casting No.  3931063  Mark IV, Oval port, open chamber with 100cc

Casting No   3964290  Mark IV, Oval port, open chamber with 100cc


Rectangular Port

Casting No  3919840  Mark IV, rectangular port, closed chamber with 107cc

Casting No  6272990  Mark IV, rectangular port, open chamber with 118cc

Casting No  12562934  Gen V, rectangular port, open chamber with 118cc

Casting No  12562932  Gen V, rectangular port, open chamber with 118cc


Aluminum Heads

Casting No  12363391  Mark IV, aluminum, oval port, open chamber 110cc

Casting No  3946074  Mark IV, L88 Zl-1,  aluminum, rectangular port, open chamber with 118cc

Casting No  12363401 Mark IV, aluminum, rectangular port, open chamber with 118cc

Casting No  14044861 Mark IV, aluminum, rectangular port, open chamber with 106cc


Chevrolet Big Block Head Casting Numbers

Casting numbers are found under the valve cover.

Casting No.YearEngine SizeCCHPPort TypeChamberIntake ValveExhaust ValveNotes
34378375-78454OvalOpen2.061.72Car or Truck
378114760-61348High Performance
381469062-64409High Performance
383773163409High Performance, Z11
385620865396109375  425RectangularClosed2.191.88Z-16 / L-37
387270266396/42798325 / 360Oval2.061.72L-34, L-35, L-36
387385866-67396/427109375Rectangular2.191.88L-78, L-72
390439066-67396/42798325 / 350Oval2.061.72L-34, L-35, L-36
390439165-67396/427107375Rectangular2.191.88L-78, L-71, L-72
390439267427107430,  435RectangularClosed2.191.88Aluminum L-88, L-89
390980266-67396/427100325 / 350Oval2.061.72L-34, L-35, L-36, L-68
391721567-69396/427100325 / 350Oval2.061.72L-34, L-35
391984067-69396/427107375RectangularClosed2.191.88L-78, L-71, L-72
391984268-69396/427106375RectangularClosed2.191.88L-88, L-89
393106369-70396/427100325OvalOpen2.061.72L-34, L-35
393314869366/396/427122OvalOpen2.061.72Car or Truck
394607469-71396/402/454118375Rectangular2.191.88Aluminum L-88, ZL-1
396428066-70427/454335, 385, 390,400OvalClosed2.061.72
396429069-70396/402/427/454100325, 330, 350OvalOpen2.061.72
396429169-70396/402/427/454108375RectangularOpen2.191.88L-78, L-71, L-72, LS-6 ,  325cc Intake Port
399382071402/454113300, 330Oval2.061.72LS-3
399924172402/454113240, 300, 330Oval2.061.72LS-3
627299071-94454118425RectangularOpen2.191.88325cc Intake Port
1005112890-9445472RectangularSemi-Open2.191.88400cc Intake Port
1014127996-01454100Vortec 7400 100cc
12363391Mark IV110OvalOpenAluminum  Performance
12363401Mark IV118RectangularOpenAluminum, Bowtie, Performance
1255816201 & UP496Vortec 8100 8.1L Truck
1256024198-01454100Vortec 7400
1256293400 & UP502Marine, GenVI
1401107789-94454118RectangularOpen2.191.88Aluminum, 295cc Intake Port
1404486189-94454106425RectangularOpen2.191.88Aluminum, 380cc Intake Port, bowtie, W port
1409618887-94454118425RectangularOpen2.191.88325cc Intake Port
1409708889-94502118RectangularOpen2.191.88325cc Intake Port


Visually identifying the Chevy Big Blocks Heads.

The first Generation of Big Block the Mark I Heads are easily identified by the W-shaped Valve covers.


Mark I Chevy Big Block Heads

Mark I Chevy Big Block Heads


Mark I Chevrolet Big Block Engine - W shape Valve covers

Mark I Chevrolet Big Block Engine – W shape Valve covers


All other Generations starting from Mark IV to Gen VII have rectangular valve covers.

Mark IV Chevy Big Block Heads

Mark IV Chevy Big Block Heads


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Chevy Big Block Head Identification – Mark IV 427 with rectangular valve covers


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