Are the new Hemi’s a true Hemi? I thiught I read an article saying that they are not a real Hemi.

Do they perform as well?


All dual overhead cam engines that I am familiar with are true ‘hemispherical’ cylinder head engines. But only Mopar can call its ‘hemisphecical’ engines “Hemis” it appears.


I really wouldn’t worry about the term hemi, it simply refers to the design of the head. At some point it was turned into a marketing gimmick. Ignore all they hype and buy the car/engine that you want.


Yes, it is marketing hype.

The “hemi” design was invented by Ernest Henry of France around 1920 or so, and was a blockbuster advancement in racing engine design for the time. In the early 1950s, this concept also enabled Chrysler to design an engine with great power potential.

Nowadays, there are many ways to extract additional power from an engine and the hemi concept is not necessary for high performance. It is simply marketing hype at this point.


My understanding is that they’re not a true hemi. They’re a “semi-hemi” as it’s called and are similar to the late 50s/early 60s Plymouth polyspherical combustion chamber engines.
So the combustion chamber is not a true domed configuration.
A bit about them here.

As to performance, they’re not bad but non-“hemi” engines on other new cars will run just as well.
A new hemi-powered Dodge was outrun, badly, by a guy with a project truck (20+ year old Chevy with a Cadillac engine for example).


The selling point of the ‘Hemi’ engine was the awesome power of a 426 ci engine with big valves, two four barrel carburators, aluminum manifold, cross flow head design, high compression, smooth half domed combustion chamber, peaked pistons, awesome head bolting/studs, Y block with cross bolted crankshaft caps, and centrally located spark plug. Not very high tech but taking the available technology to its limits. Still a push rod engine that fairly low red line.

Modern technology like overhead cams, MPFI, computer controled fuel and ignition timing, intercooled turbocharging, etc can extract the same or more horsepower from a much smaller and lighter engine and make it survive. Most performance engines are now 4 or 5 valves per cylinder, penthouse design, cross flow heads, and bottom end that can survive high RPMs.


As an owner of a 06 Dodge Charger with the “Hemi” V8, I can say that the engine does not have a Hemispherical head. It is a cross flow design with two spark plugs per cylinder.

On the other hand, My 87 Alfa Spider is a true Hemispherical head engine. Go figure.


It is not a true hemi. The original picture #1 had a smooth hemisperical valve chamber.
The new one picture #2 is not truly hemisperical.


Harley Davidson produced a “hemi” long before Chrysler did.
The 1936 knucklehead has a hemi-spherical combustion chamber and so does my 1950 Harley panhead, although the spark plugs are not centered on the chamber.
Here’s a 1956 example.


Hmmmmmmmmmm… the first picture shows a head with 2 spark plugs per chamber. Not an early hemi for sure.

The second picture shows heads with one plug per chamber as early hemis had and is labeled as a 392 hemi head. the 392 was the hemi of the late 50’s.

Could you have gotten the pics reversed?