AMC V-8s

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Amc v8.jpg


[edit] Overview

The AMC V8 has a storied history. Read about the pros and cons of both AMC V8 engines. This article will touch on the highlights.

Warning Note: Portions of the following text came from The New American Motors V-8 Engine by John F. Adamson, Carl E. Burke and David B. Potter of the American Motors Corp. This paper was first presented at the SAE National Passenger-Car, Body and Materials Meeting, Detroit, Michigan, March 7, 1956.

[edit] In the beginning

From mid-1956 on, AMC made their own V-8 engines. The company did use a few parts from other manufacturers, namely transmissions, carburetors, and electrical systems (distributor, alternator/generator, starter, etc.). Many people see a similar displacement (327, 390, etc.) engine with a Delco (GM) or Autolite (Ford) ignition/starting/charging system on it and assume the engine was purchased from GM or Ford. Anyone familiar with GM and Ford V-8s would immediately know they were looking at a different engine at first glance though.

[edit] The Packard/AMC connection

AMC only purchased one brand of V-8 from another manufacturer. That was the Packard 320 cid V-8 for the big 1955 Nash Ambassador and Hudson Hornet models, and the Packard 352 cid V-8 for the 1956 full-size Nash Ambassador and Hudson Hornet. These were equipped only with the Packard Ultramatic automatic transmission. AMC and Packard were supposed to have had a "gentleman's agreement" to cross purchase parts. This was partially to establish a working relationship between the two companies for a possible future merger. As it turned out, Packard felt it was doing AMC a favor by selling AMC V-8s. Packard sent a few bids in to AMC, but they were rejected for being too high- even though AMC was paying a premium for the Packard V-8s. AMC also discovered later that Packard was installing two head gaskets per side in the V8s they sold AMC, resulting in lower compression and less horsepower in the Packard-powered Hudson Hornets and Nash Ambassadors than the comparable Packard models.

Needless to say, this incensed AMC management. George Mason, head of AMC, ordered his engineers to get him a V-8 as soon as possible. Just 18 months after receiving the order, AMC introduced a 250 cid V-8 in mid 1956. It initially was only used in the Nash Ambassador Special and Hudson Hornet Special. The Specials were really Statesman/Wasp models with Ambassador/Hornet trim, and they were only available as 4-door sedans and 2-door hardtops. The Statesman/Wasp bodies were built on a shorter wheelbase [114.25" vs. 121.25"] and lighter [3265 lbs. vs. 3495 lbs., curb weight] than the bigger cars. Using that platform helped improve the little 190-hp 250 cid V-8's power-to-weight ratio.

Eighteen months from drawing board to production doesn't sound all that short today, but in the era of slide rules and drafting boards (no computer modeling or even calculators!) it was phenomenal. One of the ways the AMC Engineering Department worked this miracle was to hire David Potter from Kaiser-Frazer. He had previously worked with Continental Engines (owned by Kaiser Industries) on a 288 cid V-8 intended for the Kaiser-Frazer line, however Kaiser had since purchased Willys-Overland resulting in a change of its priorities; from making cars, to making the more popular Jeeps. AMC literature reports that "The entire program was under the direction of Meade F. Moore, Vice-President of Automotive Research and Engineering, and through his efforts the project was carried on cooperatively by our Kenosha and Detroit Engineering Departments. Obviously, such a division of both design and development required the utmost in teamwork by F. F. Kishline, Chief Engineer, and his assistants, E. L. Monson and J. S. Voigt in Kenosha, and by R. H. Isbrandt, Chief Design Engineer, and W. S. Berry, Chief Mechanical Engineer, in Detroit." AMC concluded in their announcement of the new engine saying "In short, our objective was an engine with maximum flexibility with regard to future displacement requirements without sacrificing any of the performance features of the power-plant. Economy of operation and manufacturing processes, along with excellent weight and durability characteristics, were all part of our aims. We think that we have succeeded in reaching these objectives, and have produced an engine that is second to none. It is an engine of which we are justly proud."

The new-for-1956 640 lb. Rambler V8 (fully assembled 'long block') was lighter at that time than all other US V8 engines, except for the 1955 Chevrolet 'small block'. And when speaking about their intake and exhaust port designs, AMC reported that "the theoretical gas velocity through the valve is lower than that of any automotive engine on the market today" & "Exceptionally close liaison was maintained with our manufacturing personnel during the design and development stages of the engine". As a result, many economies in fabricating and tooling processes were built into the original design and have since been carried through into production.

Tooling facilities for the V-8 are completely new, and are based on what we call "segmented automation." In this type of manufacturing, each basic section of tooling, although completely automatic, is not fully integrated with other sections. For our purposes, this type of tooling means increased flexibility as each portion of the line can be utilized independently of other operations.

Of particular interest is the cylinder block boring equipment, which has been designed to finish simultaneously blocks of two different bore dimensions. It contains two sets of roughing, finishing, and chamfering tools, and blocks of either bore size can enter the equipment in any mixed sequence. Each station is set to tool one size bore, and when a block enters that station, a probe automatically determines whether or not to cycle the cutting heads.

Wherefore it may be said that not only was the Rambler V8 'state-of-the-art', AMC set a new standard of excellence for the US industry.

[edit] Engine design

The Rambler V8 design features a visually identical 'Hudson X' crankcase gallery, having the main bearing webbing form an 'X' around the main bearings transferring load from the the crankshaft into the block with extreme stiffness and minimized vibration for maximum durability. The Rambler V8 shaft mounted rocker arm assemblies are visually identical to the the former Nash inline six cylinder engines. The engine features an excellent oil system, which is perhaps the best oil system of any US V8 ever made and serves as a model of oil system design theory for it's attributes.

There were three sizes of AMC Gen-1 V-8s:

  • 1956-'61 250
  • 1957-'66 327
  • 1963-'66 287

All having the same internally balanced forged steel crankshaft leveraging a 3.25" stroke with 6.375" forged steel connecting rods to the 'divorced skirt' . The 1963-up AMC (non-Kaiser Jeep corp.) versions all came equipped with revised/improved high-flow exhaust manifolds, though AMC did not change their advertised rating of 4bbl 327 from it's former rating of 270hp. From the factory, the main difference were in the bore diameter; The 250 used a 3.50" bore, the 287 a 3.75" bore and the 327 a 4.00" bore. There were three different block castings. It is rumored that early 287 blocks can be bored out to 4.00", but the best advice is to have the block sonic checked before boring. All three of these will easily take an 0.125" over bore, but beyond that is pushing the limit. 327 Rambler V8 engines have been successfully bored and stroked to 418 cid, with no known durability issues.

All 250 models use solid lifters, the 287/327s are hydraulic. These engines were also used by Grey Marine for boats in the late '50s and early to mid '60s. All the marine engines used solid lifters regardless of size.

The AMC Rambler V8 has only recently been labeled 'Gen 1' by newer AMC enthusiasts. This labeling was first used by AMC writer Frank Swygert (aka editor/forum member 'farna') in an effort to place the engine where it technically "should" be. Technically the labeling is correct; this is the first generation of AMC V-8s, AMC having been formed in May of 1954 and V-8 engine development starting in 1955. The 1966-'69 second generation models and 1970-'91 third generation models are very similar, but having a different block and head casting led to the labeling of Gen-2 and Gen-3. "Series" could have been used instead of "Generation", but "Generation" (shortened to "Gen") seemed to be the most correct description. Previously the first generation AMC V-8 had been (and still is) referred to as either the "Nash V-8" or "Rambler V-8". It was used in both Nash and Rambler branded, as well as AMC branded cars ("Rambler" was dropped from the 1965 Marlin and 1966 Ambassador, those being branded as AMC models). Technically it was built by the American Motors Corporation, not Nash or Rambler.

'Gen-1', 'Gen-2', etc. labeling ideas were first used by Chevrolet small block V-8 enthusiasts to distinguish the differences among that group of very similar engines. This has apparently led many to believe the terms were "borrowed" from the GM engine family or that a GM enthusiast created the labels. There was a small effort to distinguish between GM and AMC labels: GM models are typically labeled with all capitals (GEN-1, GEN-2, etc., sometimes with no dash), whereas Frank used a single capital (Gen-1, and always a dash). The label was used because it is technically correct and fits. GM's labeling wasn't even considered until others pointed out the similarities, and made the assumption that the labeling was "borrowed".

[edit] The Gen-2 V8

By the mid '60s the heavy Gen-1 V-8 was becoming dated. AMC engineers didn't rest once the Gen-1 was introduced though. They had been working on a thoroughly modern light weight V-8 to replace the Gen-1. The Gen-2 engine was introduced in mid year 1966 as a 290cid V8. The only thing it shares with the Gen-1 is the bore spacing. This was done so that existing boring tooling could still be used. Everything else about the Gen-2 was totally unique and new, even the bell housing bolt pattern was changed. These engines are similar to a small block, but have a larger bore spacing similar to a big block. Many people call them a "mid block", but it's just the AMC Gen-2 V-8; AMC only made one V-8 design at any given time.

The Gen-2 came in three sizes also:

  • 1966-'69 290
  • 1967-'69 343
  • 1968-'69 390

The 290 and 343 used cast cranks and rods. The 390 was intended for high performance and was made with a forged crank and forged rods. AMC stated that the primary reason forgings were used was to get the engine to market quicker; they didn't have time to thoroughly test cast components and still introduce the engine when they desired to. As a result, the AMC Gen-2 390 has a tougher bottom end than any similar displacement MOPAR, Ford or Chevy engine. Reworked AMC 390 rods are good to 7000+ rpm, whereas the other makes require replacement performance rods. A lot of work also went into development of the head. AMC heads were some of the best flowing heads on the market at the time. A typical AMC head flowed as good as or better than other makes high performance heads.

[edit] The Gen 3 V8

AMC made some improvements in the Gen-2 design for 1970, thus becoming the Gen 3. This resulted in different block and head castings and slightly larger displacement. The only change to the block was adding approximately 1/16" to the deck height and increasing the stroke accordingly.

The Gen 1 to Gen 2 block deck height difference was 1/32" nominal, or 0.033". Gen 1 was 9.175" nominal block deck height and Gen 2 was 9.208" nominal block deck height per the Performance American Style booklet AMC printed in the early '70's.

The 290 became a 304, 343 a 360, and the 390 a 401 (with a little added stroke in the crank than the 390). The 401 wasn't introduced until 1971. The 390 was kept for 1970 only by using a special piston; the pin height was altered to keep displacement at 390 inches. The head casting was changed to create a slightly larger "dog leg" exhaust port (Gen-2 heads have rectangular exhaust ports) to improve exhaust flow.

So there were four Gen-3 sizes:

  • 1970-'79 304
  • 1970-'91 360
  • 1970 only 390
  • 1971-'79 401

The AMC V-8 finally went out of production when Chrysler halted Jeep Grand Wagoneer production at the end of the 1991 model year. This makes the 360 by far the most numerous AMC V-8. It can easily be built to produce over 400 hp on pump gas. It's as modern as any other make V-8 of the time, and has as much potential. There isn't as large a selection of performance parts, but the parts still available are the ones known to work well. The parts cost a little more than the more common small block Ford and Chevy parts, but no more than any other make. Cost to build is partially offset by the very good heads. Until the Vortec L31 5.7L head was introduced, Chevy heads weren't any better than AMC heads. Now, Edelbrock has aluminum heads for the 343, 360, 390 and 401 AMC engines.

[edit] Factory power ratings

Size Years Carb Type HP @ RPM Torque @ RPM
250 1956-'57 2V 190 @ 4900 240 @ 2500
1958-'61 4V 215 @ 4900 260 @ 2500
1960-'61 2V 200 @ 4900 245 @ 2500
287 1963-'66 2V 198 @ 4700 280 @ 2600
327 1957 EFI* 288 @ ???? N/A 1957 Rebel engineering prototypes only
1957 4V 255 @ ???? N/A
1958-'66 4V 270 @ 4700 360 @ 2600  With dual exhaust
1958-'66 2V 250 @ 4900 340 @ 2600

*Bendix Electrojector. AMC decided it wasn't reliable enough at the last minute and pulled it as an available option. Sources vary on the number built, only two can be verified; they showed up at Daytona Speed week in February 1957 where manufacturers were showcasing their new products. An Electrojector-equipped 1957 Rebel was the second fastest car in Daytona from 0-60 mph. At 7.2 seconds, it was beaten only by a Rochester fuel injection-equipped Corvette that clocked a 7.0 second 0-60 time. It easily outpaced larger Hemi powered #354 and 392 cid# cars, but it must be pointed out that those engines were also in larger, heavier cars #a 1957 Rambler Rebel weighed around 3400 pounds, a Chrysler 300C weighed 5000 pounds#.

[edit] Performance upgrades

[edit] Intake manifolds

The 4V intake from the 250 and the 327 will bolt to the 287, which had no factory 4V option. The intake carb pattern is standard Holley [excluding the '57 models with the Carter WCFB, which has a smaller carb bolt pattern], and because the factory Holley 4150C used is only in the 450-500 cfm range (about right for the 250), it's easy to bolt a much more reasonably sized 600-650 cfm carb on the 287/327.

There are no aftermarket intakes made, though I have seen a rare three deuce intake once, I think it was made by Fenton, but not sure. Whereas the Rambler V8 intake manifold is a 'free-standing,' 'air-gap' design with a separate lifter valley cover, AMC Gen-2 intakes can be adapted by cutting to remove the water and exhaust crossovers and fabricating 1/4" spacer/adapter plates for each side. The ports aren't an exact match, but can be matched with the 1/4" plate. A small block Chevy intake can also be adapted, but the V angles are different and the adapter plates must be fabricated to match the angle also. The ports aren't an exact match, but can be matched within the 1/4" plate.

[edit] Camshafts

The camshaft can be reground to a more aggressive profile by any of the camshaft manufacturers. Call first, then send in your good used cam for regrinding. In the mid 1990s Crower, Isky and Lunati had a few virgin blanks, they have probably been used or scrapped by now, but it never hurts to ask!

[edit] Headers/exhaust

Andy's Auto Sport has headers for some applications. Doug's Headers sells headers for the 290-401 engines, Headers By Ed has finished and plain header flanges (and gaskets for the later engines) to fit the early 1956-'65 250-287-327 AMC V8 with shared center ports as well as the later 1966-'74 290-304-343-360-390-401 AMC V8 with either rectangular or dog-leg exhaust ports along with other various header parts like collectors and tubing.

On some heads the two outer exhaust ports match a 1.5" tube (easy to increase to 1 5/8") and the center two siamese exhaust ports match to a single 2" tube size. Sanderson makes a Cadillac header that could be converted by cutting the flange and slightly bending the tubes to match. Possibly 3-tube Pontiac V8 headers might be re-worked.

[edit] Identifying AMC engines and transmissions

The first AMC V8 engine became widely known as 'Rambler V8', and was also labeled by AMC as 'Ambassador V8' (327cid) in those models. The second all new design AMC V8 debuted in 1966 with 290 cid, then a 343 cid version in 1967 and a 390 cid version in 1968. AMC raised the deck height of their second V8 engine design in 1970, stroking the 290 to 304 cid, the 343 to 360 cid and made a new connecting rod for the 390 version. Along with the raised deck, AMC increased the head bolt size from 1/2" to 7/16" and redesigned the rectangular exhaust ports to have a raised port floor with an enlargement of the outlet beside the port floor underneath one of the exhaust flange bolts (called the 'dog leg' exhaust port to differentiate it from the rectangular port heads). The second design V8 engine has good interchangeability due to sharing the same basic architecture. The first AMC V8 engine also has near total interchangeability between the 250, 287 and 327 cid versions; only the pistons do not because cid differences were made with bore size change only.

At first glance, the Rambler V8 (also renamed 'Gen 1') looks much like the Studebaker V8; they both have similar sized rounded top large valve covers attached to the block with two large wing-nuts, a rear mounted distributor, a dual plane free standing intake manifold, a tin valley cover and a front-of-block 'free standing' water outlet manifold having the thermostat and outlet for the upper radiator hose going to the radiator. The Rambler V8 looks physically big primarily because of the large valve covers, and that the exhaust ports continue out to the edge of the block before they terminate to the exhaust manifolds. (Pontiac V8 and Ford 'FE' V8 exhaust ports have a similar design).

[edit] Identifying size

There's only one way to tell from the outside whether you have a 250, 287, or 327 cid engine. The bore is cast into the right rear top of the block just behind the head. The 250 cid block has a 3-1/2" bore, 287 3-3/4", 327 4". Other than that you have to pull the head and measure the bore. Crank and rods are the same in all three: forged steel. The cast-in number is almost impossible to see with the engine in the car, so use a mirror and try to reach back there and clean it off enough to read it. Casting numbers are way over on the side and impossible to see with the engine in the car, but here they are:

  • 250 -- 3153077
  • 287 -- 3169824
  • 327
    • 1957-'62:
      • 3144932
      • 3147230
      • 3153044
      • 3153055
      • 3153677
      • 440275
    • 1963-'67:
      • 3166463
      • 4160275

There may be others for the 250 and 287, but those are the only two I have. If you find another, let me know (!!

[edit] Engine mounting

All early 250/327 engines have four-point motor mounts. Two in front of engine, two on the bellhousing. 1963-'67 327 and all 287 cid engines have side motor mounts on the block (and one near the end of the transmission) like newer cars. The early ones don't have the side mount bosses in the block, later ones have bosses for both mounting systems, but the forward most bosses may not be drilled and tapped.

[edit] Applications

The 327 was used in the 1957 Rambler Rebel, the 1957 Nash and Hudson big cars (no Ramblers) and all 1958-'64 Rambler Ambassadors. It was also available in the 1965-'66 Marlin and Ambassador. All 1957 327 cid engines have Carter WCFB 4V carbs, and '58-'59 327 cid engines have Holley 4150c 4V carbs and 9.0:1 to 9.7:1 compression depending on application, as do all 1960-'66 4V models. The 1960-'66 base 327 has a Holley 2V carb and 8.7:1 compression. All 4V models also had dual exhaust. The carburetor is rather small at 450-500 cfm, which limits power somewhat.

The 250 was only used in the mid-1956 Nash/Hudson Specials, 1957 Rambler V-8 (other than the Rebel), and 1958-'61 Rambler Rebel models (I know, it can be confusing, but all V-8 Ramblers used the Rebel nameplate 1958-'61). Base 2V models have Carter WCD 2V carbs and 8.7:1 compression. All '57 4V models use a Carter WCFB 4V carb, and '58-51 4V models used the Holley 4150C carb with 8.7:1 compression and dual exhaust.

The 287 appeared in mid 1963. When AMC dropped the 250 there was no V-8 except for the higher priced Ambassador. Dealers complained, and AMC made the 287 available in the Classic in mid 1963. All factory 287s came with a Holley 2V carb, no 4V option. The 4V intake from a 250 or 327 bolts right on, however, and many people have done so.

[edit] Transmissions

[edit] Automatic transmissions

AMC used GM hydramatic transmissions in 1957 switching in the '58 model year to a Borg-Warner automatic transmission behind their Gen-1 engine. Only manual transmissions were used in the 1956 Specials. AMC called the GM automatic "Flashaway" and the Borg-Warner transmission "Flash-O-Matic". It's a three speed cast iron case Borg-Warner Model 8 with a vacuum modulator valve. The column shift quadrant will read P-R-N-2-D-1-L. The 1 and 2 are small.

A dash mounted push-button shifter mechanism was used in the Rambler 6 and Ambassador from 1958-'62. The American models used a column shifter. The push-buttons were marked N-R-D2-D1-L, with a Park lever under the dash. P-R-N are self explanatory. In D2 the transmission will act like a two speed. It starts in second gear and shifts to third, downshifts only to second. This was mainly used for slippery conditions such as driving in snow or ice. Using second gear prevented excessive wheel spin. Many people think they have a two speed transmission because this is the third forward position on the transmission. Slip it down to D1, however, and you'll find the missing gear! In D1 the trans shifts from first through third and back down. L (low) is first gear only, no up shifts. The trans can safely be shifted into Low at any speed. As a safety feature the trans will not shift down until it has reached a safe speed to do so. If in third it will got to second, then down to first once a safe speed is reached. It will not shift back up until shifted into D1 or D2. To manually shift through the gears start in L, shift up to D1 then as soon as the trans shifts, go back to L. It won't downshift if accelerating. When ready for third gear go back to D1.

1965-'66 models used a throttle valve cable instead of a vacuum modulator to control internal pressure. This is the M-10, internally similar to the M-8 except for the TV cable and valve body. The cable must be connected for the transmission to work correctly! Otherwise it will burn up like a cable equipped GM TH700R4 or a Chrysler transmission without the "kick-down" linkage connected. An electric solenoid inside the valve body controls kick-down (passing gear). A switch on the throttle linkage (usually on the engine) is activated at wide open throttle to force a downshift for passing, etc. It will not kick down over a certain speed, usually in the 60-70 mph range.

These are reasonably heavy duty transmissions. They are equivalent to a Ford-O-Matic or FMX three speed, which were used behind their 352 and 390 cid engines. In fact, they are nearly identical. Borg-Warner, Studebaker, and Ford formed a development team for an auto trans in the early 1950s and introduced one around 1953-'54. Ford contracted to buy 50% of their automatic transmission from Borg-Warner through 1958, and built a factory to build the other 50% on their own. That's why the same trans kit will work with Borg-Warner and several Ford auto transmissions; BUT it is not a Ford transmission! The Ford transmissions should bolt to the AMC bellhousing, no one I know has tried since the older Ford transmissions and parts availability is about the same as the Borg-Warner units.

The only "problem" with these transmissions is finding someone familiar with rebuilding them, and that there are no performance parts. Most good performance torque converter shops can rebuild the stock converter, and should be able to change the stall speed. Some are busy enough with more familiar/popular transmissions that they don't work on odd-balls like this any more. The only other performance mod is to change the line and/or converter pressure valve springs. There are no springs made specifically for this purpose, but some have either stretched or shimmed the stock springs or replaced them with other springs they have found, but this takes some searching and experimenting, so be careful!

Parts are available from several old auto trans sources. [ Northwest Transmission], Fatsco (, and Dave Edwards ( are good sources.

Kaiser Jeeps used a TH400 in the Wagoneer and pickup from 1963-'67. It's the "universal" TH400, which was the Buick Nailhead model. Buick Nailhead engines have a deep flange on the back of the block covering the flexplate/flywheel which require a shallower bellhousing than other GM engines. That shallow bellhousing left room to make an adapter without adding length to the engine/trans, so GM sold it as a "universal" model and continued production a few years after the Nailhead was discontinued. If you get one, make sure you get the 1-1/2" to 2" thick cast iron adapter as well as the flexplate and spacer. The crank will need a pilot bushing to match the flexplate. As stated, a Nailhead TH400 will work if you get just the adapter. Rolls-Royce and Jaguar used the universal TH400, among other smaller makers who didn't need enough units to warrant casting a new case. If using another AMC sourced transmission behind a former Jeep 327 with auto, make sure the thin pilot bushing is removed first.

[edit] Manual transmissions

Manual transmissions used were from Borg-Warner. The 250/287 typically used a T-85 three speed and the 327 used a T-89 three speed. Overdrive was an option -- all V-8 overdrive models used the T-85 (even the 327). I'm not positive about input shaft length, but the bolt pattern is the same as other 1950s and 1960s Borg-Warner three speeds. The T-85 uses the same pattern as the T-10 four speed, and there were a few T-10s used behind the 287 and 327 in 1966. The T-85 and T-89 used different bolt patterns to the bellhousing. The T-89 is similar in appearance to the T-85 but is a heavier built transmission.

[edit] Bellhousing bolt pattern

The AMC Gen 1 V-8 has a unique bellhousing pattern.

The AMC Gen 2 290 cid V-8 appeared in late 1966 in the American, and across the board as a 290 or 343 cid engine in 1967. The Gen 2 engines use a different bolt pattern than the Gen 1. Pre-1972 inline sixes use a smaller diameter bellhousing than the Gen 2/3 V8s) with a bolt pattern shared only with the small 1950-'54 Nash L-head sixes. All 1972 and later AMC inline sixes and V-8s use the same Gen 2/3 V8 bellhousing bolt pattern.

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