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RE: Retire the name?
By Brandon Hill (blog) on 7/8/2010 10:13:29 AM , Rating: 3
It's all about perception I guess.

RE: Retire the name?
By MozeeToby on 7/8/2010 10:25:33 AM , Rating: 2
Modern Hemi's (tm) aren't hemi's (the engine type). We designed better ignition chambers literally 35 years ago, that's why everyone stopped making them in the first place. Bringing the name back 10 years ago was just as much about perception as removing the name today is.

RE: Retire the name?




RE: Retire the name?
By djc208 on 7/9/2010 7:11:05 AM , Rating: 3
They're not a true hemispherical chamber but they are based on the same design in that the valves are located opposite each other vice adjacent as in a normal push-rod style V8. This is what makes the design so good, valves are unshrowded for better flow, air flow paths in and out of the valve are better, and the spark plug moves to a more central location.

These benefits also apply to a multi-valve "pent-roof" style head, but with more moving parts and complexity than the HEMI.

The primary reason Chrysler moved away from the HEMI in the 50's was that it was more complex to manufacture and maintain than a conventional wedge-type head.

Ironically they went back to this design for the new HEMI because it was cheaper than an OHC type design with multiple valves, but offered similar power levels. It also allowed them to more easily add the mulit-displacement system, all in a smaller package than an overhead cam engine.

The Hemispherical combustion chamber is still one of the best designs for producing power. Just look at every top-fuel dragster on the track. They all run special racing engines with hemispherical heads.

Problem is combustion efficiency isn't the best, I read it was hard to get the new HEMI to pass emissions, and is probably one reason it has two spark plugs per cylinder, but that's not an issue a drag-racer is concerned about.

