Chrysler's Early Hemi
Very few innovations in automotive technology have had as great an impact as the advent of the Chrysler Hemi. Born in the 50's it matured into an extreemly powerful and reliable engine only to die a miserable death. When Chrysler decided to bolster it's performance immage in the 60's it was the venerable Hemi that was once again called upon to take on Nascar's high banked ovals. Proving once again that what wins on Sunday sells on Monday. Chrysler's design proved so efficient that it alone is the reason that for the past 50 years nearly all major top fuel and funny car teams use derivatives of the "Hemi" design.
History:
In the late 40's Chrysler realized that it's current line of flat head 6 and 8 cylinder power plants weren't going to make the grade when matched against the new more powerful V8 designs Cadillac and Oldsmobile were planning to introduce during the 1949 model year. They also knew larger engines capable producing more horsepower would be required to haul around the new heavy weight luxo barges Chrysler currently had on their drawing boards. Seeing they were about to be out paced and out gunned, Chrysler decided to develop an engine capable of leveling the playing field. Quite frankly, what the auto manufacturer needed, to quote Tim Allen was, "MORE POWER."
Chrysler's engineers began to research possible V8 engine designs looking for something that might be capable of producing real horsepower. Eventually the decission was made to go with a conventional V8 similar to those being developed by Ford and GM, however Chrysler's version incorporated unique heads with hemispherical combustion chambers.
Although not necessarily a new idea, this design offered a high degree of efficiency both in breathing capability and in heat dissipation. The valves were placed on opposite sides of the combustion chamber. This allowed very short and nearly unrestricted intake and exhaust ports making the airflow in and out of the cylinder extremely efficient. It also allowed the valves to run cooler because of improved air movement around the valve pockets and more cylinder head area to absorb the heat of combustion. In addition the spark plugs were located in the center of the cylinder. This created a very even flame front increasing combustion efficency. All this meant that Chrysler engines could run higher compression ratios without the fear of detonation thereby creating, you guessed it, More Power.
Why the Hemi Makes More Horsepower
Demo
The hemi design also had some disadvantages. It incorporated a complicated valve train with dual rocker shafts in each head. It was also relatively expensive to produce. During the 50's Chrysler Corporation had a decentralized approach to engine building. Each division had it's own engine manufacturing facility. Given the freedom to do so, each adopted a slightly different variation of the basic hemi design. This decentralized manufacturing approach coupled with the expense of manufacturing a complicated design like the hemi eventually spelled the downfall of this mighty powerplant. Production ceased with the completion of the 1958 model year in favor of a new simplified corporate wide wedge head design.
Parts interchangeability:
Because each division produced their own version of the hemi very few parts interchange between them, however a few specific parts will interchange. All '51-'53 Chrysler front covers will fit all DeSoto engines while all '56-'58 Chrysler front covers will fit all Dodge engines. In addition, Dodge high block and DeSoto high block connecting rods will interchange. Distributors, oil pumps, and bellhousing/starter mounting flange plates will interchange except for the extended block versions and one must keep in mind that these flanges vary in thickness depending on the transmission used. Valve stem diameter is the same in all engines and length is very close so the larger diameter valves from the bigger engines can be used to improve the breathing of the smaller motors.
Within divisions some parts will also interchange. Although some low block and high block cylinder heads will interchange care must be taken when considering certain combinations. For example 392 heads are wider than earlier low block (332-354) heads. This allows the earlier intake manifolds to be used on stock 392’s, however when using early (low block) manifolds and heads on a 392 block spacers must be used because the higher deck height of the 392 will align the intake manifold mating surfaces too far apart. Conversely 392 heads won't work on a low block (331 or 354) hemi unless you use a log manifold because the lower deck height of the 331-354 combined with the longer intake runners in the 392 heads will align the intake manifold mating surfaces too close together to use a standard manifold.
There are also dowel pin diameter considerations to deal with as well as mismatched coolant passages in the lower corners with some head/block configurations. As an example ‘56 low block (354) heads will not easily fit on a ‘54 or earlier low block (331) for these very reasons.
DeSoto and Dodge heads won't interchange between high and low blocks without spacers and a lot of extra work. The manifold mounting angles are different between high and low blocks so swapping heads can be a nightmare on these motors when it comes to finding a compatible intake manifold. This is especially true with the DeSotos because of the lack of availability of any high performance aftermarket manifolds. The Dodges can use a log manifold to solve this problem if you can find one.
Hemi heads will fit poly blocks of the same family but will not fit "A" series poly motors. Chrysler 331 hemi heads can be used on the 301 and 331 Polys, and 354 hemi heads can be used on 354 Polys. No camshafts will interchange between low and high blocks of any engine family because of differing lifter bore angles.
Rebuilding an early hemi:
I'm not going to give a tutorial on rebuilding hemis here. There are a few things one needs to understand before tackling such a project though. First, early hemis are expensive to rebuild. It will cost 2 - 4 times as much to rebuild one of these motors than it will your everyday small block Chevy. For example, Kanter auto parts 1999 catalog lists the cost of Main bearings for Chrysler's 331 hemi at $175 a set. The DeSoto and Dodge hemi mains go for $125. The 331 rod bearings sell for $12 each. DeSoto for $15 each and Dodge rod bearings go for $10 ea. Compare these prices to the small block Chevy whose main bearings go for $35 and rod bearings for $4 each. The same difference holds true for other parts as well. Chrysler, DeSoto and Dodge hemi gasket sets go from between $100 - $145 and complete rebuild kits sell for over $950. The Chevy on the other hand has gasket sets available for $50 and complete rebuild kits go for about $375. This difference in price is very often a big surprise to the young guy that wants to stick a hemi under his hood. It has been the cause of many a hemi just sitting in the corner of a garage somewhere instead of rumbling down the street in all it's glory. On the other hand it is very rare to find an early hemi in a wrecking yard that can't be rebuilt. Chevy and Ford fans aren't so lucky.
The second item you need to be concerned about when rebuilding a hemi is parts availability. Kanter auto parts and others can supply just about anything you need for a stock rebuild, however performance parts for some of the less popular hemis can be a real challenge to find. Especially the DeSotos. Performance parts for these motors are virtually non existent. Some factory equipment was supplied way back when but it's very difficult to come by. Limited performance equipment is available for the Dodge hemi but by far more parts are available for the Chrysler 331-392 series than any other. The good news is that as these engines are being rediscovered and as they become more popular manufacturers are beginning to reintroduce performance parts they stopped making 20 or 30 years ago. Already places like PowerPlay and Hot Hemi Heads are providing parts and services for the early hemi enthusiast and more are sure to follow.
The Chrysler hemi had a cast iron block. Thin wall casting techniques had not come into practice in the early 50's so these motors were quite heavy for their size. All were produced with 2 bolt main caps, and forged crankshaft and connecting rods. Most engines came with cast aluminum pistons and hydraulic valve lifters with the exception of some of the high performance versions which left the factory with forged pistons and solid lifters. These motors can be identified by four bumps in the valve covers between the spark plugs.
The 51-53 Chrysler 331's had an extended belhousing cast into the back of the block which limits your transmission choices. Some outfits have reintroduced adapter kits which allow the GM 4 speed to be bolted to these blocks. These adapters are a welcome addition to the parts bin for many enthusiasts. For years these extended blocks were considered useless (except for spare internal parts) and many of the blocks were trashed by short sighted hot rodders. DeSoto, Dodge and Plymouth never produced hemis or polys with the extended bellhousing.
In '54 Chrysler fell in line with it's other divisions and introduced a more conventional belhousing design making the installation of modern GM and Chrysler automatic transmissions much easier, however adapters are still required. They're available from several sources but be prepared to pay between $300-$400 for a good one.
Hemi cylinder heads were cast iron as were the intake and exhaust manifolds. 2 bbl. and 4 bbl. versions were available while the high performance line usually had a dual 4 bbl. low rise manifold equipped with early Carter WCFB carbs. To illustrate how scarce DeSoto performance parts are, if you could find a factory dual quad manifold with carburetors and linkage intact you could easily sell it for $2000 possibly more. Not bad for a days scavenging in the local wrecking yard.
The bottom line:
The early hemi is being rediscovered by enthusiasts all over the country. This means that more parts will become available and that some of the out of production parts will probably be reintroduced. On the down side the increased demand for early hemis will make the price go up. Gone are the days when people would practically give these things away. Current prices for complete motors vary from $300 to $1500 depending on size and what part of the country you're in. The author was actually in the right place at the right time once and picked up a high performance DeSoto 341 hemi for a hundred bucks. Three years later I purchased a 330 DeSoto parts motor and it cost me over $300.
When thinking of investing in a hemi do yourself and every other hemi enthusiast a favor. Take into consideration your budget and how bad you really want that hemi. If you think it's going to be too expensive then don't do it. The world already has enough hemis sitting in the corner of garages collecting dust. These engines are not cheap to rebuild and require lots of part hunting, but once completed nothing, absolutely nothing can match the class of a hemi under your hood. (Chevy and Ford fans objections duly noted.)
Information for this site was collected from several web sites, "The Hemi White Paper", "The Street Hemi Users Guide", Mopar Magazine, "The Ultimate Guide to American V-8 Engines: 1949-1974", and Street Rodder magazine. If you are a hemi expert and find any inaccuracies in this text or on the data pages, please e-mail the correct information and it will be added/changed as necessary. Thanks.
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