First, let’s examine what type of manifold the 426 Street Hemi was produced with.
The 426 Street Hemi engine intake manifold is a dual-plane design engineered to fit two 4-barrel carburetors. It is made of aluminum, and the basic design remained the same from 1966-1971 with some slight variations with its markings.
The intake manifold has two heat tube holes in the rear of the manifold. There are two heat tubes which attaches to the two heat holes. The tubes connect to the right side exhaust manifold providing heat to the intake manifold.
The heat improves cold temperature operation and makes the Street Hemi more suitable for typical driving conditions in the street.
The remainder of this article will explain how to identify a 426 Hemi intake manifold for each year. These topics include the date code, casting numbers, markings and various stampings for each year.
426 Hemi Intake Manifold Casting Numbers
The intake manifold has a dual casting number meaning it has two different casting numbers for the same intake.
The two castings numbers for the 426 Hemi intake manifold are:
The casting numbers are located on the front of the manifold in the center and were present for each year of the Hemi Engine production years, 1966-1971.
The 2780544 casting number is located closer to the carburetor and the 2780543 is located closer to the front of the manifold.
426 Hemi Intake Manifold Stampings and Markings
The manifold had various different stampings and markings throughout the years. Let’s take a look at each one and explain where they are and for what years they may be found.
This will prove helpful for identifying the year a 426 Hemi intake manifold was used since they do not have any date codes.
A round hole is found in the rear of the early 1966 intake manifolds. It’s located on the top of the manifold between the two exhaust heat tube holes.
Its purpose is to access the middle of the three attaching screws (bolts) on the rear rail. The two other screws and the three screws (bolts) in the front of the intake are visible and accessible without the use of an access hole.
The access hole is not found on any manifolds after 1966 because the front and rear rails have locating dowels instead of the screws.
The photos below are from the 1966 service manual intake manifold removal instructions. Note how it states, “One attaching screw (bolt) is reached through the hole at the rear of the manifold. Use special Adaptor Tool C-4021 (Fig. 5).”
The photo below is from the 1967 service manual intake manifold instructions. Note how any reference to the hole and screws has been replaced with, “there are three locating dowels at each end of the manifold.”
The 1967 instructions are the same for the remaining years to 1971.
MLT Letters, Serial Number and 319 on the Rear
The 1966 and early 1967 intake manifolds have the following located in the rear:
- Serial number consisting of letters and numbers.
They are on the top in the rear of the manifold above the manifold heat tube holes. See the photo below.
The meaning of the markings and serial numbers are not exactly known. The speculation is they were stamped there by the foundry for internal control or documentation.
I have noticed almost all of them contain the letter P near the beginning and the letters C or G near the end. Also, the letter A is common as the last letter.
Once the Pentastar appears on the front of the manifold (later in 1967) these markings are no longer on the intake manifold although the rear serial number pad is often seen minus the numbers.
The letters DPCD are seen on the top, front of the intake manifold to the right of the casting number towards the front of the manifold.
They are found on the 1966 and early 1967 Hemi intake manifolds.
The four letters are on two lines. The top line has the DP and the bottom line CD.
The P is larger than the other letters and extends the length of both lines. See the photo below. The Pentastar on the later manifolds replaces the four letters and is located in the same area.
The letters WBAC M1 are seen on the top, front of the Hemi manifold between the two casting numbers.
They are found on the 1966 and early 1967 Hemi intake manifolds, the same as the DCPD.
Once the Pentastar appears, the WBAC M1 letters and number are no longer found on the manifold.
The 1966 and early 1967 intake manifolds did not have the Pentastar emblem. Later in 1967 a Pentastar emblem (Chrysler logo) appeared slight to the right of the casting numbers.
It is located on the top, front and is in almost the same location as the DCPD on the earlier manifolds.
A Pentastar manifold does not have the WBAC M1 between the casting numbers. The casting numbers also moved closer to each other.
An S within a circle is located to the left of the 2780543 casting number and appears for the first time on the Pentastar manifolds.
The Pentastar emblem remained on the intake for the remainder of the Hemi engine production. Therefore, it is found on the following manifolds:
- Later 1967
The letter P is stamped next to the Pentastar emblem. It is found on the later Pentastar manifolds all the way through to 1971.
The size of the P is slightly larger or smaller and it may be sideways or upside down.
I suspect the P is a carry over from the P in the four letters DCPD, but I have no concrete evidence of that. That P was larger than the other three letters making it seem more significant and the reason to maintain it on the later manifolds.
Some people associate the location of the P to a particular year, but I haven’t seen enough consistency to make a determination.
Swollen Area on Intake Runner #7
The 1970 and 1971 intake manifolds have a swollen area on the top of the number seven intake runner (driver’s side closest to the firewall).
It appears a repair was made to the manifold casting creating a slight bulge in that area.
There is a heat shield that attaches to the bottom of the intake manifold. This prevents hot oil from contacting the underneath of the manifold making it cooler.
It attaches with eight bolts around the perimeter and two bolts in the center. The heat shield is installed in all years, 1966-1971.
I first learned about Mopar engines, including the 426 Hemi, when I assembled my first Mopar engine about 38 years ago.
Read more Mopar engine intake manifold articles:
Just one year ago, I assisted a friend bolting and torquing down a 426 Hemi intake manifold. The process can be exhausting. Check out my article, 426 Hemi Intake Manifold Torque Specs.
If you have any questions about the 426 Hemi intake manifold, send us an email found specifically on our contact page.
More Mopar Engine Articles
- Dodge and Plymouth Engine Service Manuals 1966-1971
- Google Books: Chrysler Engines 1922-1998