Hemi vs Wedge

Landyacht

Landyacht

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I could never understand all the hype about the hemispherical cylinder head design. What benefit does it have over the wedge? I've heard allot of bad things about the early hemis such as being more prone to detonation due to the large combustion chamber and poor quench which caused overheating issues . In recent years they have ben able to correct allot of those problems with the modern hemis but is there any real benefit or is it mostly hype?
 
The shape of the combustion chamber and the location of the spark plug make for a very complete and efficient burn and better power than the wedge. Nothing wrong with a wedge though.
 
In regards to Chrysler B and RB type V8 engines -

For street use, I think the wedge head design has proven itself many times over. It is reliable, can be optimised easily, and does not limit the kind of performane that is needed for the most demanding heavy duty use.

For unlimited race use, the hemi head has its advantages. Which is why Chysler adapted it to the RB block...for racing. They had to offer it as a production piece to get NASCAR and NHRA to allow it to race.

Techically, the hemi allows for larger valve size potential and maximum flow efficiency is easier to achieve with a hemi head design.

For any reasonable street use, and even a lot of race uses, the wedge works fine.


All the new Hemis coming from Chrysler are mainly marketing talk. Whatever their advantages may be, they have virtually nothing in common with Hemis from the 60s and 70s.
 
I own all wedges but I fully understand how and why the hemispherical chamber is better. It was built to be a killer race engine. not always happy on the street at lower rpm's but a beast on the track. the new hemi is NOTHING to sneeze at either. those heads with dual plugs and highly efficent chambers. they are pulling 700 horse from naturally aspirated 400-417 inch motors! That is over 1.68 hp per cube. I love my 440's but I don't see alot of true 740 horse naturally aspirated 440's running around.

http://www.hotrod.com/events/popula...-at-the-amsoil-engine-masters-challenge-2014/
 
300Nutter said:
All the new Hemis coming from Chrysler are mainly marketing talk. Whatever their advantages may be, they have virtually nothing in common with Hemis from the 60s and 70s.
Click to expand...

300Nutter is completely right

They are great motors, but I believe they aren't actually true "hemi's"
 
3 advantages for Hemi over a wedge

1. Port arrangement is not squeezed between pushrods, in high rpm racing bigger straighter ports wins period.
2. Valves are angled toward the center of the bore the further they open the less shrouded by the cylinder wall they become, better flow
3. Centrally located spark plugs means flame front travels downward from top center, the combustion chamber shape being a section of a sphere concentrates the combustion pressure straight down on the piston, a wedge ends up wasting some its pressure toward the cylinder wall.
All modern engines are trying to achieve these efficiencies no matter how their valves are driven or what they are called, this is why so many modern engines from all manufacturer's are showing up with coils going straight through valve cover, like a certain engine from 64 years ago.

MOPAR RULES!!!!!!
 
Chrysler discontinued the hemispherical design in 1959 mainly due to size and weight of the hemi V8's. They didn't fit well under the newer low profile hood designs of the day, among other reasons.

The hemispherical combustion chamber design goes way back in internal combustion engine history. The Dusenberg engines were hemi's, as were several other high end American and European engines.
Chrysler was the first to add "hemi" to it's marketing campaigns when their first V8's were introduced in 1951. and "Hemi" became identifiable with Chrysler.
 
Chrysler first learned of the cylinder head design in the war when they helped improve the reliability of aircraft engines. Thanks Will for poo-pooing on my rallying speech with all this Duesenburg talk lol.
 
The hemi head was a drastic improvement over the wedge heads of the time. However, technology improves and the dead space and bulk of the true hemispherical chamber and the piston required ultimately meant it had to go. With some combining of design elements the modern wedge is better for all around power, emissions, reliability, economy, packaging, and NVH.
 
70bigblockdodge said:
3. Centrally located spark plugs means flame front travels downward from top center, the combustion chamber shape being a section of a sphere concentrates the combustion pressure straight down on the piston, a wedge ends up wasting some its pressure toward the cylinder wall.
Click to expand...
The Buick 425s and 401s had the centrally located plugs. those motors where built around the same era as the hemi
 
One View Point

Having been been around both designs nearly all my life, it always boiled down to this. On the street where it boils down to torque, the wedge motors pretty much had their way with the Hemi cars, especially the real 440 *6 pack cars. On the track was a different story, when you could get the revs to utilize the much better breathing head design, game over. Your mileage may vary, but that how I see it.


Landyacht said:
I could never understand all the hype about the hemispherical cylinder head design. What benefit does it have over the wedge? I've heard allot of bad things about the early hemis such as being more prone to detonation due to the large combustion chamber and poor quench which caused overheating issues . In recent years they have ben able to correct allot of those problems with the modern hemis but is there any real benefit or is it mostly hype?
Click to expand...
 
Landyacht said:
The Buick 425s and 401s had the centrally located plugs. those motors where built around the same era as the hemi
Click to expand...

3 things not just one. A poly has a better combustion chamber than a LA engine, which has a better combustion chamber than a big block.

>HP = >$$$$$ easy math.
 
Customer: Build me an engine.
Engine builder: How many horsepower?
Customer: How much can you give me.
Engine builder: How much money you got?
 
The new Chrysler HEMI engines are NOT a true hemispherical design. Close, but not a true Hemi.

The infamous Mitsubishi 2.6L engine that Chrysler used in the '80s K-cars and derivatives (Stan's favorite Mopars of all time!) was a true Hemi design.

The people that claim that Chryslers (and Fords) are sooooo expensive to build, are people that ONLY know Chevy engines. And there is very little difference in the actual cost to build any of them. I've never, ever had problems "finding parts" for a Mopar engine...another spurious claim by the ignorant Chevy guy.

Now, when you enter 426 HEMI territory (and Ford 429), then yeah, you are talking cubic money to build either.
 
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