Whence came the old Mopar 318"?

[Jack_Vines]

Greetings, All old hemi Mopar experts,

If memory serves, the evergreen Mopar 318" V8 evolved from either the Dodge or DeSoto hemi/polysphere engines. Which was it and what was the first year of the in-line valve 318"?

Actually, a bit of research answered my own question. See if I have my facts straight. It began with the 1953 Dodge hemi and in 1955 was converted to the A-engine polyspheric head, grew to 318" and was converted to in-line valves with the LA-engine version for the 1965 273" Barracuda engine, grew to 318, 340 and 360, still used in Jeep and Dodge trucks today. A fifty-year run is not bad for any engine.

thnx, jv.

[Bob Kinker]

The 273, 67 and later 318 and it's derivitives are a different class of engines. Different block, heads etc. Some of the newer 318 parts can be used on the 318 Poly (wide block) engines. The water pump, starter, crank, distributer, harmonic balancer, valves, etc from the 318/340 can be used on the 318 Poly.

In fact, the cross section on the Poly combustionb chamber is very much like the combustion chamber on the "new" Hemi. www.geocities.com/polyman64

<img src="http://forums.aaca.org/images/graemlins/wink.gif" alt="" />

[Jack_Vines]

Good catch, Bob,

Right science always comes around again. Doing the research I mentioned, the A-engine was the basis of the redesign of the LA series, sharing all the basic architecture, which is why the components you mention will still interchange.

thnx, jv.

[Guest imported_Bill-W]

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Greetings, All old hemi Mopar experts,

If memory serves, the evergreen Mopar 318" V8 evolved from either the Dodge or DeSoto hemi/polysphere engines. Which was it and what was the first year of the in-line valve 318"?

Actually, a bit of research answered my own question. See if I have my facts straight. It began with the 1953 Dodge hemi and in 1955 was converted to the A-engine polyspheric head, grew to 318" and was converted to in-line valves with the LA-engine version for the 1965 273" Barracuda engine, grew to 318, 340 and 360, still used in Jeep and Dodge trucks today. A fifty-year run is not bad for any engine.

thnx, jv. </div></div>

Actually, the A block poly shares nothing with the Dodge engines. The A block has larger bore centres permitting bigger bores. The largest size the Dodge block got to was 325 - and that was with a raised block (higher deck).

The A block started at 277 and 303 in 1956, adding 301, 313 and 318 in 1958, and 326 for 1959 only. The A block came in only one deck height and is incorrectly labelled a "wide block". In truth, the A block width differs from the LA block in exterior diminensions by 100ths of an inch.

The A block heads, though, with their poly heads and splayed valves, were much wider the LA block heads with their wedge heads and valves all in a row. Take the heads of an A block and off an LA block, and you could not tell the difference.

The LA block received some changes to the block to permit room for the steering box on the A body. But the big changes were in the heads.

LA blocks came as 273, 318, 340 and 360. The LA block came to an end a couple of years ago. Today's 5.2 and 5.9-litre engines share nothing with their predecessors.

Both the Dodge and Chrysler engines came as either hemi or poly while the DeSoto was always a hemi with no poly versions.

Bill

Vancouver, BC

[Jack_Vines]

Hi, Bill,

Just trying to keep it all straight. You are saying the A-block of 1956 shares nothing of the architecture of the earlier hemi Dodge or DeSoto?

thnx, jv.

[Guest De Soto Frank]

That would be correct.

The "single-rocker shaft engines" from MoPar in the '50s were stand-alone designs, not adaptations of the first-generation Hemi.

They would have perhaps shown some "family resemblance" in terms of physical attributes, but they were not a "re-worked Hemi".

The 2nd-generation Hemi of the '60s was adapted from the RB family of big-block wedge-motors. The block casting was significantly modified, in terms of webbing/gussets to support the main bearings, and other mods, but there is a common origin in that case.

[Rusty_OToole]

You can go nuts trying to figure out the welter of engines and transmissions used in Chrysler products in the 50s.

The 318 was indeed its own engine.

Chrysler's first V8 was the Chrysler FirePower hemi of 1951. It was followed by the DeSoto Firedome of 1952. These were completely different engines, but the DeSoto was a carbon copy of the Chrysler in a reduced size.

Then came the Dodge Red Ram hemi in 1953. This was a modified DeSoto. The bore, stroke, etc are different but crankshafts heads and other parts interchange. In the 50s it was possible to mix and match parts from both engines to get a certain displacement for a certain racing class, or to hop up your Dodge using DeSoto parts.

You would think that Plymouth would have followed suit in 1954 but it didn't. The Plymouth V8 debuted in 1955 and this was a totally new engine, practically nothing interchanges with previous engines. If you compare head gaskets you can see the big Chrysler has the widest bore spacing, the DeSoto/Dodge is the smallest, and the Plymouth is in the middle.

The Plymouth was made as a 277, 303, 313, and 318 Poly head only, unlike the other Chrysler products there was no hemi head.

They even made a short lived 260 in 1955 at least they announced such a model, whether they ever sold any I don't know.

Meanwhile Chrysler Dodge and DeSoto all had polysphere engines of their own, made by putting Poly heads on the hemi block. This is good to know for the interchange possibilities but does make things complicated on the engine ID and parts ordering front.

This is just skimming the surface. There were many permutations of displacement and horsepower, plus raised block versions of the various hemis in 1957/58. Not to mention the transmission options.

After 1958 things got calmed down a little with the well known B and RB engines replacing the Dodge DeSoto and Chrysler engines and the 318 used as a base V8 in Dodge and Plymouth.

Then they redesigned the 318 as a 273 with wedge heads for the Valiant and Dart, then took it out to a full 318 for the big cars, and this became the new base V8. The crankshaft, rods, and most bottom end parts stayed the same. The heads intake and exhaust were different. The block was redesigned, mostly to lighten it. I'm not sure if the heads will interchange on the 2 blocks but I know the crankshaft will interchange.

The 318 begat the 340 and the 360. The 340 was a high performance 318. I believe it used the old thicker cylinder cores from the original 318 because its bore was the 318 bore plus .135 and the max overbore on the old block was supposed to be .125 while the new thinwall block was only allowed .060.

It also had better heads with bigger valves.

The 360 was a 340 with slightly smaller bore, long stroke crankshaft, and the same heads with slightly smaller intake valves and open combustion chambers. This engine was meant to replace the big block 361 and 383 in the heavier cars.

Next redesign was the Magnum truck engine around what, 1990? 1992? Somewhere in there. This mainly involved a new cam design with roller lifters and new heads.

[Guest black56hawk]

Well, this may be old news, but:

The Chrysler, De Soto and Dodge hemis were three separate engine families. Don't see how a De Soto crank would fit in a Dodge hemi, since the De Soto bore center-to-center spacing (not the actual bore size) was 4.3125" while the Dodge bore spacing was 4.1875" (the Chrysler's bore spacing was 4.5625").

There were poly versions of the Chrysler hemi and the Dodge hemi. There never was a poly version of the De Soto hemi, although the low line 57 De Sotos used Dodge poly engines.

The bore spacing of the all-new 277 Plymouth engine introduced for the 1956 model year was 4.46" (the 55 Plymouth engine was actually a Dodge poly, and some low-line 56 Plymouths continued using the Dodge poly until production ramped up). Although the Plymouth engine was new, some of the dimensions are continued from the Chrysler hemi, including crank to cam distance. The Plymouth poly was offered in 277, 303 versions in 56, later in 313, 318 and 326 versions. The 303 and 313 were Canadian offerings, although the 303 was also put into 56 Plymouth Furies. When Chrysler corp. began to standardize its engine offerings in the late 50s, the Plymouth engine evolved into a corporate motor, and was offered as the base V-8 in the 59 Dodge - but with a .040 overbore (making it a 326) just so the then mid-size Dodge would have a bigger engine than the low-price Plymouth.

At least one reason for the all-new Plymouth engine in 56 was that the early hemis didn't have enough cubic inch potential. At 392 cubes, the Chrysler hemi was maxed out, and its bore was barely larger than its stroke. The later tall-deck versions of the De Soto and Dodge hemis were undersquare, with a larger stroke than bore, and still had only 315-325 cubes (Dodge) and 330-341-345 cubes (De Soto).

The Mopar big block was introduced for the 58 model year with 350 or 361 cubes; 383 (low and tall deck versions) and 413 came the next year, eventually grew to 440 cubes with a shorter stroke than a 325 Dodge hemi/poly. The 318 poly (326 was offered in 1959 only) stayed around through 66. A 273 wedge based on the 318 poly tooling was introduced in 64 - it is essentially a small bore 318 poly with wedge heads. A 318 wedge was introduced in 67, 340 wedge in 68, and 360 wedge in 71. Cranks, distributors, timing chains, water pumps, oil pumps and probably timing covers and oil pans are interchangeable from 318 poly to wedge. 360 wedges have larger main bearings.

[Rusty_OToole]

Re the DeSoto and Dodge being brothers. I base this on the the fact that the crankshaft, rods, and other parts are interchangeable between Dodge and DeSoto blocks. Hot rodders in the 50s took advantage of this to hop up the Dodge block using DeSoto parts for more displacement. And also, by mixing and matching components, you could get different displacements to fit in different racing classes. This was done for Bonneville records and for hydroplane racing mostly.

[Guest black56hawk]

The De Soto hemi is physically larger than the Dodge hemi - the block is longer, the heads are longer, the rocker arms and the rocker covers are longer, the cylinders are farther apart (the bore center-to-center distance is greater) - which means both the main bearings and rod throws are farther apart. You'd have to explain to me how a De Soto crank could possibly fit in a Dodge hemi, and how the crank throws could possibly be in the same place when the cylinders are not.

Besides, the 56-7 tall deck De Soto hemis and tall deck Dodge hemis have the same 3.80 stroke, so there would be no reason to swap even if you could (the De Soto has more cubes with the same stroke because it has a larger bore, which it CAN have BECAUSE it has a larger bore spacing).

Now what the hot rodders did do was put Dodge hemi heads on a 260 inch 55 Plymouth motor (because it was really a Dodge engine anyway), or Chrysler hemi heads on a 300 inch 1955 Windsor poly - to fit certain classes at Bonneville. Perhaps this was the interchangability you were thinking about.

[Rusty_OToole]

My information came from some research I did years ago trying to sort out the welter of different engines and transmissions used by Chrysler Corporation in the 40s and 50s.

The part about Dodge and DeSoto crankshafts being interchangeable came from various contemporary magazine articles about hopping up the engines.

I just checked an old Motor Repair Manual and found out that in 1953 and 54, both cars had identical main bearing specs but the DeSoto rod bearings are bigger.

I have also personally compared the Desoto, 318, and Chrysler blocks and laid the head gaskets one on top of the other. I found the Desoto block was the shortest, the Chrysler the longest, and the 318 was in the middle. This was all in hopes of finding a way to put hemi heads on a 318 block. But it won't work.

So a lot of the info I have is second hand, but some is based on 40 years of working on old cars. I wouldn't be the farm that I am right but I want you to know I am not just talking thru my hat. It would be interesting to tear down a 53 DeSoto and a 53 Dodge hemi side by side and compare, but I don't think there is much chance of me having that opportunity.

[Guest black56hawk]

If you had laid a Dodge head gasket next to the others, it would have been the shortest of all. Main bearing diameter is not the issue for interchanging cranks; the problem is the distance between the mains and the location of the rod throws and those distances simply are different in two motors with different bore spacing. I have every issue of Hot Rod Magazine from January 1950 to December 1980 and many other vintage mags. I've never seen any article that says you can put a De Soto crank in a Dodge.

Mopar V-8's of the 50s are not hard to understand if you realize there are basically five groups, with varying bores and strokes (and therefore cubic inches) in each group. Viz:

Chrysler, 1951-58, 4.562 bore spacing, low and tall deck, hemi and poly (in 354 hemi version, also used in 57 Dodge D-501)

Plymouth, 1956-2002, 4.46 bore spacing, poly only till 66 (also used in 59-up Dodges), wedge 67-up

De Soto, 1952-57, 4.3125 bore spacing, low and tall deck, hemi only (used in De Sotos only)

Dodge, 1953-58, 4.185 bore spacing, low and tall deck, hemi and poly (poly versions also used in 55 and some 56 Plymouths, and some 57 De Sotos)

Corporate big block, 1958-78, 4.80 bore spacing, low and tall deck, wedge (all years) and hemi (66-71), wedge versions used in all Chrysler corp products, hemis were Dodge and Plymouth only

[Rusty_OToole]

Thanks for the info. I stand corrected.

There is a little more to it than that. When you consider the long block and the short block, tall block and low block, plus polysphere versions of all 4 engines, plus the Plymouth block in various sizesplus "borrowing" from each other to supplement their own engine lines, plus the B and RB that debuted in 58.

Then add in the flathead sixes, in 2 blocks made in various sizes, plus special Hydrive blocks, plus truck versions, plus exclusive Canadian engines and you could go nuts figuring them all out.

Lucky for me I'm already nuts Ha Ha.

[Guest black56hawk]

Yes, agreed that the interchange possibilities even within each group was very complicated in the 50s. Once Chrysler Corp settled on the corporate big block, the corporate small block (formerly the Plymouth engine) and then the corporate (slant) six in the late 50s, things got much easier.