Educate me on the "hemi" engines

[green69rt]

I've seen a lot of "back-and-forth" on the various hemi blocks. So what are true hemis and what are not.  The old desoto, chrysler, etc Hemis had true spherical combustion chambers, right??  What about the new engines, still true hemis or something else.  Let the discussion begin............

[ws23rt]

This could get long and complicated but it need not.

The term "Hemi" of course comes from the shape of the combustion chamber.

A true hemi is a technicality.  In the real world if someone calls an engine a hemi and that term is excepted as being correct that it is a hemi.

Terms and words tend to evolve as to their meaning.  Opinions about what is correct are just that opinions.

Chrysler has used and promoted the term hemi so much that the it doesn't mean what it was to begin with.

I asked a motor head guy that I work with (when on the topic of hemis) if he knew what a hemi was. He said no.  I asked him if he knew what a wedge head was. He said no.

So a true hemi would mean that the shape of the combustion chamber be a true spherical shape. And if it is not true than it is not a hemi

If the tooling that made the early hemis were to be off a bit and the combustion chambers were in fact not true hemispheres than we all have been living a lie.---I can live with that just fine.

[cdr]

to add to what was said by ws23rt,the intake & ex valve are in line,NOT side by side,the valve arrangement of the hemi promotes better exhaust scavenging,& the main thing is un shrouding  of the valves for better air flow.

[polywideblock]

people call 318 poly 's semi- hemi 's what's with that    

                           not trying to hijack thread or anything  and you were asking about old Desoto's etc. 

[Cooter]

people call 318 poly 's semi- hemi 's what's with that    

                          not trying to hijack thread or anything  and you were asking about old Desoto's etc.  

'Loosely' describes the polypherical chambers. Kinda like the Big block Chevy. Halfway to a hemi.
some say the only 'true' Hemi's were the 331-354-392 versions.  The 426 valves in degrees, weren't exactly straight across.
so I guess one could state, based on that, the true hemi has been going downhill ever since 1958.....

[green69rt]

So, aside from the relatively small variations in valve angle on the early hemis, they seem to really be the real thing.  Now what about the engines that have been produced lately, say 2005 and on.  Do they have fully hemispherical combustion chambers?   If not then what do they have?  And... do other manufacturers make a "hemi" engine but don't call them that because Mopar has a lock on the term??

[Mike DC]

Lots of 4-bangers and some 6cyl engines are Hemis, from various brands.  But nobody bothers to make a selling point out of it on anything other than V8s. 

[polywideblock]

here's the fly in the ointment , a 3.5 litre all aluminium hemi   Toyota V8 made in the mid 70's for a japan only limo .

they are very popular for hotrods over here 

                                                                   

                                   

                           


  http://www.youtube.com/watch?v=zdAcLYwJoFY   worth a watch as it shows the motor running from all angles

they have always fascinated me     and are real hard to get

[hemihead]

I believe the new Hemis are what is more of a Pent Roof design combustion chamber .

[Dino]

I believe the new Hemis are what is more of a Pent Roof design combustion chamber .

I've heard the term poly with the new hemi's a lot...but hemi sells better than poly.

[John_Kunkel]

The new Gen III Hemi is a Hemi in name only.....since Chrysler copyrighted the word they can call anything a Hemi.

[odcics2]

2 valves, directly opposite with the spark plug(s) on the top of the chamber.
4 valve version is a pent roof design.

Poly had the spark plug canted to one side and the valves 'twisted'.