Pics of new and old HEMI engines broken down

[th59718]

Over on the Honda/Acura forum they have a few threads pertaining to the 300C and the HEMI engine -- mostly about how the new HEMI is not really a HEMI or how Chrysler is exploiting the HEMI name with its new engine or how tacky the “HEMI” TV ads are. One enlightened member posted this comment and there hasn’t been another posted there for days. End of story!

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Stumbled across this topic and it seems that there's a lot of misconception about the new "hemi" engine. I'll demonstrate for you exactly what the controversy is. Here are pics of the original "hemi" cylinder heads.

community.webshots.com/album/138915209ljJFHE

As you can see from the pics, the hemi head gets its name from the HEMIspherical combustion chambers. Note that the chambers are perfectly hemispherical.

Here are also pics of the new hemi.

As you can see from these pics, the new hemi heads have a modfied hemispherical shape; they have "quench" pads on the sides of the chambers. The pads cut into the chamber, distorting the perfect hemisphere- this is what has caused the controversy. These pads come into very close proximity to the piston at TDC, forcing the fuel mixture away from the sides and towards the spark plugs. This significantly reduces detonation and helps with fuel economy. I have highlighted the quench pads in the last picture. You can also see that the chamber retains the basic hemispherical shape, and the valvetrains for the new and old heads are nearly identical. The new engine also has dual spark plugs, which ensures that all the fuel is burned- a flaw in the original hemi design. The chambers were so big that a significant portion of the fuel would go out the tailipes. The hemi design is better for flow- the new heads are said to flow in the 280 range @.500 lift.

BTW, there is no perfect cylinder head design. The Pentroof chamber is great, but it has it's purpose, and is not the best design for all engines. That particular configuration is best suited for 4 valves per chamber, which itself lends itself to overhead cams. Chrysler wanted to keep costs to a minimum with this new engine, thus the pushrods, and the hemi combustion chamber.

Hope I've dispelled some of the myths surrounding this new engine

[GMLind]

Nice, and I like to hear from car enthusiests who are enlightened enough to give credit where credit is due. I get real tired of listening to the brainwashed who think their car or manufacturer preference is the only way to go and anyone who doesn't agree is stupid. Nice to have link with pic's. also.

[II kings 9:20]

Thanks for getting this info out, I too was cornfused.

[JonW]

I just learned something too. I had no idea the 300C had 16 spark plugs!

[LWOOD]

Great pics. Thanks for taking the time to explain. There is also a great Popular Hot Rodding article elsewhere on the forum that is a DETAILED piece on the construction and materials involved with the HEMI.

[th59718]

Originally Posted by LWOOD

There is also a great Popular Hot Rodding article elsewhere on the forum that is a DETAILED piece on the construction and materials involved with the HEMI.

I saw that article too and printed it out. It was a great article if you're into the technical details of engine design or looking at modifying the engine in the future for higher performance. There were air flow curves and HP/torque curves and recommendations for possible improvements - although the author's opinion was that for a stock engine the new Hemi is very well designed. Unfortunately, these forums are getting so big I wouldn't know where to look for it again as a reference to those interested. I'll do a search of the forum or dig out the article and post a reference here later.

OK. Found the article (looks like the March, 2004 issue of Popular Hot Rodding) using Yahoo search for those that are interested:

http://www.popularhotrodding.com/tech/0403phr_hemi/

BTW, in my search, I found another interesting article and a whole new site that might be of interest to some:

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