Chrysler Hemi-The Elephant”-4 of 5

Chrysler’s second generation Hemi arrived in 1964 as a race engine barely disguised as a production part, and its nickname came honestly. The 426 stood 10.72 inches at the deck, spread its bores 4.80 inches apart, and needed an engine bay most cars did not have. Roughly 11,000 street versions were ever built. Read on for how NASCAR banned it, why the valvetrain made it so expensive, and what made it the default choice for nitro racing.

There is a specific kind of engineering decision that only makes sense if you have already decided to win. In 1964 Chrysler made one, and the result was an engine so large, so heavy and so expensive to produce that fewer than a rounding error’s worth ever reached customers. Its own builders nicknamed it after the largest land animal on earth, and they were not exaggerating for effect. Sixty years later it remains the benchmark by which every other American production engine of the era gets measured, and yet the numbers behind it are stranger than the reputation suggests. This entry, the fourth in our Hemi series, covers the engine everybody actually means when they say the word.

Five Years Off, Then Back With a Vengeance

Chrysler had walked away from hemispherical combustion chambers in passenger cars for roughly five years before reviving the concept as the second generation, or G2, and selling it under the name that is now a corporate trademark. The new 426 cubic inch engine was not a warmed over version of anything. It was conceived to dominate, and it was released into a competitive environment where dominating was still legal. The name that stuck to it around the shops, the elephant, was earned honestly by its physical presence rather than by marketing.

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The Dimensions That Earned It the Nickname

The dimensions tell the story better than any horsepower figure. The block carried a deck height of 10.72 inches, or 272.3 mm, with bore spacing of 4.80 inches, 121.9 mm. Add the enormous hemispherical heads with their splayed valves and shaft mounted rocker assemblies and you have an engine that simply would not fit in a great many cars without modification to the engine bay itself. Every one of those dimensions was chosen to allow airflow and valve size that a wedge head engine of similar displacement could not match. Physical bulk was the price of admission, not an accident of casting.

NASCAR 1964 and the Ban That Followed

It went to work immediately. Plymouth Belvederes carrying the new engine raced on NASCAR circuits in 1964, and the result was so lopsided that the sanctioning body took action. For 1965 the Hemi was ruled out because too few units were available to the public in showrooms, which was a polite way of saying Chrysler had built a purpose-designed racing engine and called it a production part. Chrysler’s answer was to make good on the letter of the rule. The street version arrived for the 1966 model year, and with genuine showroom availability established, the engine returned to the ovals.

Why That Valvetrain Cost So Much to Build

The expense was in the valvetrain. A hemispherical chamber puts the intake and exhaust valves on opposite sides of the chamber at a substantial included angle, which requires two separate rocker shafts per head and a far more complicated set of pushrods, rockers and adjusters than a conventional wedge design. Every one of those parts costs money to machine and time to assemble. What Chrysler bought for that money was breathing at high rpm. NASCAR mandated two valves per cylinder, but by increasing the valve angle relative to the piston, the engineers could fit dramatically larger valves into the same bore, and the chamber geometry left room for more if rules had ever allowed it.

Oversquare by Design, and What That Bought

The 426 is oversquare, with a 4.25 inch bore against a 3.75 inch stroke, 95.3 mm. That ratio favors rpm and makes the engine friendly to boring beyond stock, which mattered enormously to the drag racing community. The street Hemi was available in most high performance Dodge and Plymouth models from 1966 until 1971, and famously turned up in the compact A-body Dart and Barracuda for 1968 as a purpose-built package that was never intended for casual street use. Buyers paid dearly for the privilege. On many cars the Hemi option represented a significant fraction of the total price of the vehicle before any other boxes were ticked.

The Street Hemi and Its Very Short Option List

Ordering one was its own exercise in commitment. The Hemi could be specified across the high performance Dodge and Plymouth catalogue, which over the years meant the Charger, Coronet R/T and Super Bee on the Dodge side and the Belvedere, Satellite, GTX and Road Runner on the Plymouth side, then the Challenger and Barracuda once the E-body arrived for 1970. Checking the box did not simply add an engine. It mandated heavy duty driveline components, specific rear axle ratios, upgraded cooling and suspension, and it changed the insurance conversation permanently. It also came with real ownership obligations, because the solid lifter valvetrain required periodic adjustment that a typical owner was not equipped to perform. Chrysler knew this, and dealers were expected to handle it. A great many Hemi cars were sold to people who did not keep up with that schedule, which is part of why the survivor count runs well below the build count.

Nitro, Blowers and a Block That Never Quit

On the track the block proved almost impossible to kill. Stroked, blueprinted and fitted with a roots supercharger on the intake, running nitromethane through the injectors and dumping into open zoomie headers, the Hemi became the default architecture for funny car and top fuel competition and has remained the basis of that world ever since. Take any modern nitro engine apart and the ancestry is unmistakable. Very few production engines from any manufacturer in any country have had that kind of afterlife in a form of racing their designers never anticipated.

Eleven Thousand Engines, Endless Demand

All of that reputation rests on a production run of roughly 11,000 street engines. That scarcity is the reason a documented, numbers matching Hemi car today occupies an entirely separate tier of the collector market from an otherwise identical big block car. It also explains the vigilance around authentication, since the gap in value between a real Hemi car and a well-executed tribute is large enough to motivate people. If you are shopping, buy the documentation before you buy the car. Share your thoughts in the comments below.

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