What makes an engine a hemi?

[InfiniteNothing]

The old Hemis had hemispherical engine heads but those have been largely replaced today by better designs so my question is, is there like a new hemispherical head design or are all the caracters on TV rather uneducated suckers for marketing

[DarkFury]

The simple answer...

The intake valve and the exhaust valve are 180 degrees away from each other in the combustion chamber of the engine.

The detailed answer...

http://auto.howstuffworks.com/hemi.htm


The main difference between the "OLD" Hemi (including the Legendary 426):

The simple answer...

The "New" Hemi design incorporates a second spark plug to burn the excess fuel that wasn't previously burned by the first plug.

The detailed answer...

http://www.allpar.com/mopar/new-mopar-hemi.html

[mechmike0034]

The simple answer...

The intake valve and the exhaust valve are 180 degrees away from each other in the combustion chamber of the engine.

Let's try 90 degrees. If they were 180 degrees apart, the valves would face each other. Also the combustion chamber is shaped like a hemisphere (half-a-sphere)as shown best in the close-up view of the graphic linked below.

Notice in the graphic that the valvestems (in green) form a 90 degree or right angle due to the "rounded" combustion chamber in the cylinder head:

http://static.howstuffworks.com/gif/hemi-diagram.gif

The new design is more pentroof than hemispherical in my book, but DCX can call it whatever it wants as they owe no one an apology for that engine design. It is very well done. DCX and GM both get criticism from folks who think that pushrod engines are archaic, but the Hemi and the Gen III small block are both superior engines to Ford's OHC modular V8, in my opinion.

[InfiniteNothing]

From the mopar link:
Intake valve angle 18 degrees
Exhaust valve angle 16y.5 degrees

Just wondering but how do you get 180 or 90 degrees out of that?

[mechmike0034]

From the mopar link:
Intake valve angle 18 degrees
Exhaust valve angle 16y.5 degrees

Just wondering but how do you get 180 or 90 degrees out of that?

Are we talking Classic or NG Hemi?

I (and the howstuffworks graphic) was talking about the original old-school Hemi.

The angles you mention sound like NG and refer to the angle from "straight up" or parallel to the cylinder bores.

Like I said, the new Hemi's combustion chamber design is more pentroof than true hemispherical, but it is still one helluva engine.

To answer your original question, yes, the name is more marketing than actual design. GM did something similar - they stuck a "shark-fin" in the intake ports of some of their V6 and V8 engines to promote combustion chamber swirl for performance and emissions, and the marketing folks called it Vortec.

[DarkFury]

Let's try 90 degrees. If they were 180 degrees apart, the valves would face each other. Also the combustion chamber is shaped like a hemisphere (half-a-sphere)as shown best in the close-up view of the graphic linked below.

Notice in the graphic that the valvestems (in green) form a 90 degree or right angle due to the "rounded" combustion chamber in the cylinder head:
My bad... I stand corrected.

I was thinkin' 180 degrees as positional (as if you were looking at it straight down not the angle of intake and exhaust...) but I'll defer to your definition above, as all I really care about is that it does work good :D