Thread: General Hemi Info Part 1

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The new HEMIs are starting to show up but I suspect that the price will be a major deterrent to all but the very high buck hot-rodder for a while. Additionally, you will also either have to live with computer controlled fuel management and ignition systems or find a work-around.

The 426 HEMIs are also pretty much in the high buck hotrodder area. They are out there, both original versions and the newer crate motors and they DO demand a premium price. Your chances of walking into a wrecking yard and finding one in a wrecked Charger or Road Runner are going to be about non-existent. Go ahead and ask, you never know, if nothing else the yard owner could probably use a good laugh

For us poor boys, that pretty much leaves the early style HEMI. This is not a necessarily a cheap proposition either (when compared to other more modern and readily available engines). Even if you find and buy an affordable, complete and somewhat running example of an early HEMI, chances are it will need to be rebuilt. The machine work it will require shouldn’t cost any more than doing any other V8, however the cost of parts can hurt. You are looking at over $200 for rod and main bearings, $200-250 for cam and lifters, $125+ for a gasket set and on and on (these prices are based on the more popular 331/354/392 engines, parts for the Desoto and Dodge versions can be considerably harder to find and more expensive).


Mechanically, all the early HEMIs were good engines. They were made of quality materials and for a mass produced passenger car engine made in the 50's the tolerances were held pretty close. In spite what many believe there is nothing magic about a HEMI. The head design allows
the POTENTIAL for the most HP per CI of any design, but in stock form many of the early HEMIs were small displacement and low compression and as already mentioned there is a pretty hefty weight penalty associated with running one. The key to really keep in mind is that no matter how efficient an engine of 350 cubic inch is it’s still a 350 cubic inch engine (or 241 or 392 or what ever). When trying to make HP the old rule that bigger is better still applies.

Doing a 1954 and up non-extended bellhousing Chrysler 331/354/392 engine is a pretty straight forward proposition at this point. Parts to rebuild them and both new and used speed parts are readily available. The extended bellhousing version of the 331 or the Desoto and Dodge HEMIs can be done but do have a couple of drawbacks in my opinion.

1. Compared to the latter (54-56) non-extended bellhousing 331/354s they have smaller ports and valves, and the water crossover was in the intake manifold rather than at the front of the heads. This limits the choice of intake manifolds to a large extent. This in and of itself is not a show stopper a simple head swap can cure this and there were a bunch of latter 331/354 heads out there. (Avoid the 57/58 392 tall deck heads for the 331/354 low deck engines. They physically fit, but are wider and unless you are planning on running a 2 piece log manifold your not going to find an intake that will work.


I recently came across a bit more info on the 331 heads.
I should expand this a little bit as it's not quite correct or complete. In 1954 Chrysler increased the valve size on the 331s (the water still exited through the intake). In 55 the cooling system was redesigned and the 55 331 requires a special 1 year only head gasket. The bigger valve 54 heads would be a direct bolt on, but I'm not sure about the latter 55 up heads.


2. There is a VERY limited availability of transmission adaptors to allow the use of a more modern tranny on the extended bellhousing 331 HEMIs. If you do get one of these engines and plan on running either a stock transmission or are planning on using an adaptor that bolts to the existing bellhousing be sure you also the lower half of the bellhousing as the transmission also bolts to this and it is where the starter mounts. The adaptors for most latter automatics require cutting off of the tranny bellhousing, and the stick setups I've seen are limited to Ford top loaders. This to me is the main reason for the average hotrodder to avoid them. The trimming of the bellhousing (either on the block or the tranny if the automatic adaptor is to be used) is NOT for the faint of heart or mediocre machine shop. With access to a good machinist it is doable and the parts to convert to a short bellhousing and stick are not really all that expensive but IT"S GOING TO BE LABOR INTENSIVE!!!!! ($$$). I discuss cutting the bellhousing for a 4 speed in this post.

http://www.clubhotrod.com/forums/sho...threadid=14794


3. The Desoto and Dodge HEMIs are sometimes referred to as the “baby HEMIs” both due to their displacements and their physical size. The Desoto is slightly shorter and narrower than the Chrysler HEMIs and the Dodge (Red Ram) HEMIs are smaller still. The difference is not a lot, but they might be just the ticket for a really tight engine compartment. These versions also generally seem to command a little less money than the 354/392 HEMIs. The real down side is that there is generally a lot less information available, the parts to rebuild them can be very difficult to find and very expensive when you do. Additionally new aftermarket speed parts are virtually non-existent and not much used speed equipment shows up either.