By Steve Magnante
As we celebrate 50 years of 426 HEMI® engine power, let’s remember that Chrysler Corp. actually created three distinct generations of this fabled dome-head power plant. The first generation appeared in Chrysler vehicles in 1951 and — with unique variations for use in Dodge and DeSoto models — was offered through the 1958 model run. The second generation is the one racers love. That’s the mighty 426 HEMI engine of the 1964–1971 era.
Of course, the third generation of the HEMI engine is what’s driving so much excitement at Dodge these days. Available in 5.7-, 6.1-, 6.2- and 6.4-liter variations, this third generation of HEMI engine delivers wonderful power — but with the reduced emissions and improved fuel economy required in today’s world.
But getting back to the second-generation HEMI engine, the 426, there is one odd detail that has confused engine builders and restorers for decades. It is the fact that the 1964 and 1965 editions of the 426 HEMI take a unique rocker cover and gasket. These items are designed to fit the unique 1964 and 1965 cylinder heads and do not interchange with the far more prevalent 1966-up HEMI engines. So what gives? Let’s explore together and discover the surprising detail that makes 1964 and 1965 HEMI heads so different from all the rest. Hint: this detail also made driving a 1964 or 1965 Race HEMI engine a true workout experience!
This 1964 Dodge 330 Race HEMI sedan is a clone but accurately represents the no-nonsense attitude of the 1964 and 1965 Dodge Race HEMI package cars. Designed specifically for sanctioned ¼-mile drag racing in Stock, Super Stock and Factory Experimental categories, all deadweight was eliminated from the body of the car, and frills such as air conditioning, a heater, power brakes and power steering were strictly not available.
About that power steering … When Dodge decided to offer a slightly de-tuned Street HEMI engine for the 1966 model year, they knew a certain percentage of buyers would want to order power steering to ease the task of driving — and parking — their 425 horsepower Street HEMI-powered Coronets and Chargers. So, the left-hand end of the tooling and patterns used to make the Street HEMI cylinder head was re-contoured to make room for the filler neck of the Chrysler power steering pump. The finger points to the revised 1966-up Street HEMI head. Note that the 1964 iron Race HEMI (bottom) has a straight end. Apparently the Dodge engineers figured it would cost less to refigure the head casting than to modify the power steering pump unit just for Street HEMI applications.
This is the view inside the rocker covers used on 1964 and 1965 Race HEMI engines. Again, note the straight lines indicated by the ends of the stamping. The right-hand end of this cover mates to the left-hand end of the Race HEMI head as installed. For 1966-up, Dodge also redesigned the rocker cover to suit the curved contours added to the heads.
Here is what happens when a 1964 or 1965 Race HEMI rocker cover is placed atop a 1966-up Street HEMI cylinder head. Note the difference in shapes and the gap that results. No amount of silicone sealer will prevent massive oil leaks here. The big problem facing owners of 1964 and 1965 Race HEMI engines is the present day unavailability of new rocker cover gaskets. Even in the seventies, these gaskets were becoming difficult to find. After all, records show that only 271 Race HEMI engines were made in 1964, plus another 300 or so in 1965, so demand has never been great. By contrast, over 12,000 (and counting) “curved-end” Street HEMI engines have been made since 1966. Rocker covers for these engines are easily obtained.
Speaking of 1965 Race HEMI heads, here’s a clean example. Identical in virtually every way to the 1964 item, the big difference is how aluminum replaced cast iron for the 1965 unit. This was part of a concerted effort to reduce weight for the 1965 A990 Race HEMI package cars. Power was unchanged, but the weight of each head dropped from 60 to 27 pounds for a nifty 66-pound weight reduction off the front tires of the car.
On this power-steering-equipped Street HEMI engine, notice how the power steering pump filler neck and cap tuck close against the leading end of the driver-side cylinder head. Without the curved-end revision added to the Street HEMI head in 1966, the pump would not fit and power steering would not be possible without costly changes to the pump, accessory drives and pulleys.
Now that you’re up to snuff on this subtle — but critical — difference between Race and Street HEMI engines, go back to the first picture of the ’64 Race HEMI engine clone and ask the question: “Does it have the correct heads and rocker covers?” If you answered “no,” you’re correct. That’s because original 1964 Race HEMI heads are incredibly scarce today, so most builders of clones settle for the next-best-thing, regular Street HEMI heads — with the curved left-hand ends. Now we know!