Who Invented the 426 Hemi and Designed It: The Chrysler Hemi

The Hemi Engine was such a huge success and is iconic in the automotive industry. For this reason many people wonder who invented the 426 Hemi and designed it.

The 426 Hemi Engine was invented by the Chrysler Corporation headed by President Lynn Townsend who commissioned and approved the development. Assistant Chief Engineer Willem Weertman and Racing Program Coordinator Tom Hoover made design decisions and overseen the team of engineers.

Let’s take a closer look at these people and others who played some part in the development of the Hemi Engine. In addition, some interesting facts and stories about the Hemi design and how it all started.

People Who Invented the 426 Hemi and Designed It

The following people had major roles in inventing and designing the 426 Hemi Engine:

  • Lynn Townsend: Chrysler President
  • Willem Weertman: Assistant Chief Engineer of engine design
  • Tom Hoover: Racing Program Coordinator
  • Rober Cahill: Product Planner Chief Engineer
  • Bob Rodger: Special Car Manager
  • Don Moore: Powertrain Engineer
  • Frank Bialk: Designed and drew the engineering layouts for the Hemi head and valve gear.
  • Harry Weslake: Founder of Weslake Research and Development in England.
  • Forbes Bunting: Chrysler engineer responsible for the intake manifold design.

How the 426 Hemi Was Invented

Here’s how the 426 Hemi was invented.

Lynn Townsend – Chrysler President

Lynn Townsend, the Chrysler President, had two teenage sons who would hang out on Woodward Avenue in Detroit. They told him Chrysler lacked street credibility and the Chrysler products did not relate to younger people.

Lacking street credibility is hard to imagine today, but prior to the 426 Hemi and the muscle car era, this may have been true. Of course after the Hemi, Six Pack, RB blocks and the 340, Chrysler had more than enough street credibility up the you know what.

Lynn decided he was going to change their image and develop race engines to compete on the tracks.

By doing this would improve their brand which should translate to sales at the showrooms. The 413 and 426 wedge engines were a direct result of this initiative. The wedge designs were great at the drag strip and drag racing in the streets but were lacking success at Nascar.

Pontiac won the 1963 Daytona and Lynn wanted to dominate at the ovals also. He approved and commissioned the engineers to build something new to compete in time for the 1964 Daytona 500.

In early spring of 1963, there was a meeting including Bob Rodger, Don Moore, Tom Hoover, Bob Cahill and Willem Weertman. The team was asked what would it take to win the 1964 Daytona. They recommended they adapted the Hemi head design used in the 1950s to the RB wedge block.

Jack Charipar

A presentation headed by Jack Charipar, Director of Chrysler’s Product Planning, was made to the executives. He convinced the executive board the Hemi would get their mission accomplished and bring Chrysler the oval track victories eluding them.

They got the approval and in April 1963 the 426 Hemi project was born and started.

How the 426 Hemi Engine was Designed and Made

Tom Hoover

Tom Hoover, the Racing Program Coordinator, often called the Father of the 426 Hemi. He surmised the most efficient way to save money and produce power was to use the 426 Max Wedge block. Then adapt the Hemispherical combustion head design used in the 1950s to it.

Those Hemi Heads were used in cars and trucks from 1951 to 1958 and in 1959 for some trucks. They were used were the Chrysler FirePower, DeSoto FireDome and Dodge Red Ram.

Read more about those early ones in my article, Hemi Engines.

Another major decision Tom made was to tilt the cylinder head inboard. This would limit the length of the exhaust rocker arm, help the position of the exhaust pushrod and increase the intake flow.

Frank Bialk – Hemispherical Combustion Chamber

Frank Bialk was assigned to do the engineering layouts of the new Hemi head and valve gear. The heads were modeled after the previous Hemi head design used in the 1950s by Chrysler.

His first drawing of the new Hemi head was dated March 23, 1963.

Slight modifications were made like adding another bolt per cylinder and tilting the head in.

Tom Hoover said much of the accolades go to Frank and he had the ability to visualize designs.

Tom said certain people are put on this earth with three dimensional insights, not many other people had. Frank Bialk was one of those people.

Read about the earliest 426 Hemi Engine in existence, Earliest Surviving 426 Hemi Engine Block.

Harry Weslake

Harry Weslake‘s name doesn’t come up much when people talk about Chrysler or the Hemi. I think it should.

He was a consultant for Chrysler and was located in England. He optimized the design and shapes of the head design models made by Frank Bialk.

According to the book, Chrysler Engines 1922-1998, by Willem Weertman, Harry bench tested the designs for air-flow.

His testing gave significant improvements to air flow which was incorporated in the pattern equipment before the first head castings were made.

He also helped Chrysler design the wedge head design. Harry and several others developed a 6-cylinder Hemi in 1948 for Jaguar.

He also helped design the Plymouth Weslake DOHC V8 raced in an Indy car at Dover, Delaware, in 1969. The Plymouth, which was a 318 cubic inch block with 340 heads, was raced to victory with Art Pollard as the driver.

Harry Weslake has been described as England’s greatest expert on cylinder head design.

Forbes Bunting

Forbes Bunting was a Chrysler engineer responsible for coming up with an intake manifold design.

Forbes had a knack for storytelling and an ability for making people laugh. His motto, “It doesn’t have to be true; it just has to be funny.”

Willem Weertman

Willem Weertman was the Assistant Chief Engineer of engine design. He was very much involved in all aspects of designing the Hemi.

Weertman called in Larry Adams, in charge of the race Hemi testing program at the Highland Park testing engine lab. At the time they only had durability testing for passenger car engines.

Weertman and Adams developed durability testing schedules for race engines. They came up with the idea of running the Hemi in the lab identical to the demands made on the engine during an actual 500 mile race. This included straightways, turns and pit stops.

Larry Adams, in charge of dyno testing, reported the blocks were cracking in the bores prior to the finish of the simulated 500 mile test.

The solution would be to revise the existing block cores at the foundry to increase the amount of metal around the bores.

Initially, the new blocks had voids which prompted Weertman to fly to the Indianapolis foundry and approve a slight modification which proved to work out okay.

Louie Taylor, casting specialist and Earl Pinches were also instrumental in modifying the new casting cores.

Did you ever wonder how many liters your Mopar has? Find out in my article, How Many Liters is a 426 Hemi? You can figure it our for any engine.

People at The Engine Lab in Highland park

Troy Simonsen and Steve Baker worked at the engine lab in Highland Park. They checked for cracks, zyglowed the pistons, magna glowed the blocks, heads, cranks and rods. They tested and analyzed everything requiring mechanical development.

Steve Baker said it took about 80 man hours to assemble a Hemi for testing not including machining.

Baker said their dynamometer was only a 400 horsepower dyno so they had to slide rule the observed power past 400.

Ed Moeller (department manager), Baker and an operator were present for the first horsepower pull. Ed gave the okay to test the Hemi which risked damaging the dyno.

426 Street Hemi Invention and Design

Nascar Rule Change for an Engine

For the 1965 race season, Nascar ruled any engine raced in the cars had to be mass produced for the general public.

As awful people make this new rule out to be, it actually was a good thing. Due to the new rule, the 426 Street Hemi was invented.

We have the annoying, pain in the you know what rules to thank for the iconic street Hemi. The one engine so many people drool over at car shows, auctions and meets. The ultimate Hemi bringing in millions at auctions, making some people rich.

Robert Cahill and Bob Rodger

Bob Rodger, special car manager and product planner Chief Engineer Robert Cahill asked engineering to make a street Hemi.

They drafted a letter which was dated January 6, 1965 and was addressed to styling Manager J.C. Guenther and engineer H.R. Steding.

Their letter stated the following:

“Because of continued requirements for an ultimate performance dragstrip, and street-type engine with expanded usage, the following change in the engine lineup has been agreed upon after discussion with the affected areas. Please release a hemispherical combustion chamber engine for ‘B’ Series with the following general characteristics:

  • Intake manifold to have two four barrel carburetors.
  • Cylinder block to maintain cross tie bolt bearing caps.
  • Cast iron exhaust manifold.
  • Solid lifters are acceptable but not preferred.
  • Pistons – forged acceptable and thermally controlled preferred.
  • Manifolding and camshaft to be designed to give the best high speed power possible while still maintaining a reasonably drivable vehicle for summer and winter.
  • Automatic and four speed [manual] transmissions required. 4-speed to receive development priority.
  • No air conditioning required for “B” series.
  • Limited warranty is acceptable for the “B” series.

Projected production volume expected is between 5,000 and 7,500 cars, which will take effect in the start of the 1966 production year. This engine to replace the eight barrel wedge requested in Production Planning Letter of 8/5/64.

Their biggest concern at this point was street ability. They already knew the engine was durable by withstanding the 500 mile races.

The detuned Hemi would have to require less maintenance, use pump gas and run good in any weather.

Just six days later, W.J. Bradley, of Product planning, issued a product description of the street Hemi package which met the criteria laid out by Cahill and Rodgers.

The most visible change would be the intake manifold with inline two four carburetors. There was a heat riser to help warm up the engine. The cam was milder and the compression was lower.

The Hemi heads basically remained the same except for some minor adjustments to the front rails of the heads.

Learn more about those changes and others in my article, The Difference Between a Street Hemi and a Race Hemi.

Approximately 38 years ago was one of the first times I saw the Hemi in person. It was at a local car cruise hangout where people would set up street races. It’s a moment I’ll never forget. The Hemi was in a ’68 Road Runner with a big cam.

The First Hemi Muscle Cars

The 426 street Hemi Engine was released into cars for the 1966 production year. It was available in muscle cars and in plain Jane trim cars like the Plymouth Satellite with hubcaps and bench seats as shown in the photo below.

Learn more about each one of those cars in my article, The First Year.

Charles “Pete” Hagenbuch

Charles “Pete” Hagenbuch, Chrysler engine development engineer, who later became head of production engine tuning, was one of the people developing the Street Hemi.

Test engineers working for “Pete” were Doug Livermore, Richard Winkles and Doug Wilmot.

I learned about the invention and design of the 426 Hemi by reading Mopar books, articles, magazines, seminars and watching videos for approximately 37 years.

If you have any questions or if you have more information you’d like to contribute, send us an email found on our contact page.

Find out if people are building new ones in my article, Do They Still Make a 426 Hemi?

Read More Hemi Articles

Hemi Specifications – Complete Engine Specs

How Fast is a Hemi? 1/4 Mile & 0-60 Results

Article Resources


  1. Thanks for the history lesson! I had a 69 Roadrunner with the383. Loved that car. Wish I still owned it’

Leave a Reply

Your email address will not be published. Required fields are marked *