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AMC 390 Engine of the Week Video |
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1982AMCConcord
AMC Addicted Joined: Jul/13/2012 Location: Kenosha, WI Status: Offline Points: 1287 |
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Posted: Dec/02/2021 at 7:25am |
Found this video recently. It's from early 2021.
It gives a really good technical overview of what parts they used to achieve 530hp/520 lb.-ft. Hopefully some of you will enjoy this or find some of the information useful. |
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PHAT69AMX
AMC Addicted Joined: Jul/07/2007 Location: West Virginia Status: Online Points: 5919 |
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458 HP AMC 290 based 304 in 1968 3.842" Bore x 3.280" Stroke Crucible & Birth of the R4B and CrossRam from Hi-Performance CARS magazine 1968 All the majors are investing big bucks into ponycar road racing. But American Motors, the smallest investor, is showing the biggest return and has become THE AM IN TRANS AM (article excerpt) : "... The highest (1968 AMC 290 based 304) dyno reading achieved was 458 hp at 7,000 rpm ... and the average race engine would put out between 445 and 450 horses at this speed... Is that ok for the little 290 American Motors engine that nobody thinks of when they think of hot small-block combinations ?..." full excerpt, 1968, The AM in Trans Am : The bulk of the (AMC) engine performance development last year (1967) was done with the intake manifolding. The (FIA SCCA TransAm) Rules call for a "factory production" manifold or optional service design. AM had no high-performance manifold available for the V-8 engine. Hot rod supplier Vic Edelbrock, Jr. had a big-port aluminum design for the AM engine (the R4B) to mount a large single four-barrel (the Holley List 3916 950 cfm 3-barrel & others, like the List 4223 850 cfm Center Squirter, BUT the SCCA TA Rules specified ONLY the Number & Maximum Size Diameter of manifold openings, NOT the Venturi Size Diameter or even any specific Brand or Model of Carburetor!): but this was basically a street manifold, and not competitive with the exotic Camaro and Mustang ram-type designs on the racetrack. Anyway the Javelins used the Edelbrock (R4B) design with a big 950-cfm Holley three-barrel carb (Holley List 3916-S AMC Part No. 4485730) at their first race in Sebring (March 22, 1968) -- and (the AMC 290 based 304 engine) developed a rather astonishing 410 hp at 6,800 rpm on pump gas! (The manifold was made legal by putting a factory part number on it.) This output wasn't too far behind the early '68 Camaro (302) and Mustangs (302) with DUAL four-barrels: Revson proved to have reasonably competitive lap speed -- and managed to finish fifth. But even while this was going on the AM management had commissioned Vic Edelbrock to design, test and tool a dual-quad cross-ram manifold (the STR-11) for the remainder of the '68 season. This turned out to be entirely unlike Edelbrock's famous cross-ram hot rod manifolds for Ford and Chevy engines that he introduced in the early 1960's. These had separate plenum chambers for each carb over the rocker covers, with long 15-inch passages going across the top of the engine to ports on the opposite bank. The new Javelin (STR-11) design used just one big plenum going the full width of the manifold casting, with the two carbs dumping direct into this huge chamber. The shorter 10-inch passages come off the bottom of this chamber, crossing over to ports on the opposite side. It's kinda like the famous Chrysler "rambox" single-four-barrel manifold for NASCAR track racing with the Hemi engine. The reasoning behind the new design is obvious: The engine doesn't have to pull below 5,000 rpm in Trans-Am racing, so the more restrictive double plenums were not necessary. And the shorter cross passages give their major ram boost in the 7,000-8,000 rpm range instead of in the 5,000-6,000 range of the 15-inch passages. This gives more peak horsepower. And this was proved right now when the little 304-cuber gave 40 more horses on the dyno with the new manifold and two 600-cfm Holley carbs! ( ? Holley List 1850, 4210, 4224, or what ? article doesn't say, vintage original Edelbrock STR-11 AMC Crossram Instructions call for a pair of MODIFIED List 1850 600's for street use & a pair of Holley List 4224 660 Center Squirters ! otherwise & for the 390 ) The highest dyno reading achieved was 458 hp at 7,000 rpm -- and the average race engine would put out between 445 and 450 horses at this speed,, Is that ok for the little 290 American Motors engine that nobody thinks of when they think of small-block combinations for various hot rod and racing applications? Maybe we'd better start remembering this basic engine in our plans. It's small, it's light, it has a rugged bottom end (with the usual beef-up tricks), and it apparently has better port design in the heads than we figured. It must -- because this 450 hp is as much as the were getting from the tunnel-port 302 Mustangs at the end of the season. And the Penske Camaro 302 didn't get much over 460 horses in '68. Think that over very carefully. I was very surprised myself.
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1982AMCConcord
AMC Addicted Joined: Jul/13/2012 Location: Kenosha, WI Status: Offline Points: 1287 |
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Thanks Phat. Seems pretty obvious that AMC's engine was very well developed.
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