A typhoon is a tropical cyclone with winds 75 mph or more that occurs in the north Pacific, west of the International Date Line. It's a fierce and respected storm and the name conveys the public image little American Motors Corporation hoped to project with its new line of V-8 engines, introduced for the 1967 model year. The engine would be offered in two displacements and available in the complete line of American Motors cars, which included the Ambassador, Marlin, Rambler Rebel and Rambler American. Mounted in front of both manual and automatic transmissions, the curb weight of the cars would range from 2,900 to 3,900 pounds.
The Typhoon engine would be completely new and represented a significant step forward for the product line. Initial planning for the 290/343 cubic-inch V-8 engines was started in March, 1963. The previous V-8 engines were recognized as excellent performers and enjoyed a reputation for durability. However, with advancements in design and manufacturing technology, it was apparent to the corporation that a new engine would be beneficial to both the customer and AMC.
The Typhoon V-8 was required to be lighter and smaller than the power plants it was to replace. In addition, the mandate was to improve on the already superior durability the brand was known for while producing more power and using less fuel. A new challenge was a reduction in exhaust emissions that would be required by the federal government in a few years.
As with any project of this magnitude, the costs were always a consideration, especially for the tooling. It was acknowledged that there were two methods to minimize the capital investment.
One was to maintain a maximum commonality and interchangeability with the upcoming Torque Command inline six-cylinder engine, which was just being completed. The second method was to maintain certain dimensions and configurations of the original engine so that the existing V-8 tooling could be revamped to produce a portion of the new engines. Design studies indicated that undesirable compromises would be necessary to fulfill this objective; as a result the Typhoon V-8 was produced almost entirely with new tooling as quality and engineering took priority over the demands of company bean counters. This commitment to excellence will be established as the Typhoon V-8 is explored in this installment of Mechanical Marvels.
The block was a slim-wall design using fine-grain cast iron. The casting process required only four cores: A body core and two water jacket cores of the hot-box type, as well as an oil-sand rear core. Eleven oil-sand cores were required for the old engine. The use of only four cores represented a major advancement in the manufacturing of cylinder blocks.
Displacements of the 290 and 343 cubic inch engines were provided by bore diameters of 3.75 inches and 4.08 inches, respectively, using a common stroke of 3.28 inches. Cylinder bore spacing was 4.75 inches, which provided room for large valves and ports for excellent volumetric efficiency while maintaining relatively close bulkhead spacing for good crankshaft support from the five main bearings.
Five bolts per bore were used to attach the cylinder head and the valley area of the block was employed for an oil return path.
The front engine cover housed the distributor, oil, water and fuel pumps and was die-cast aluminum. It also provided the mounting and passages for the full-flow oil filter and housing which held the relief valve.
Due to the thin wall casting and advanced engineering, the new engine was 83 pounds lighter than the former V-8 while also enjoying a smaller external dimension.
The crankshaft was made of a cast pearlitic material and had large-diameter rod and main bearing journals to provide adequate overlap for stiffness. During the initial development, failures were encountered at the rear of the crankshaft between the rear web and the #4 rod journal fillet juncture. The original compound radii used for the fillet created a high stress level at this point. The eventual solution consisted of increased radii of the fillet, a revised cheek contour, and elimination of the crank pin lightening holes. The consequence of eliminating the lightening holes was that an internal balance could not be used. External balancing amounting to 5.87-oz.in. for the 290 and 8.82-oz.in. for the 343 was mandated. This residual unbalance was built into the vibration damper and into the flywheel or the flexplate, whichever was used.
Crankshaft durability was greatly affected by torsional vibrational modes. The control exerted by the damper design was tuned to 201 cycles per second. AMC's desire to keep the double torsional amplitude to below 0.25 degrees was accomplished and the crankshaft design passed all tests with no failures.
The engine used two distinct piston styles, conformatic and autothermic-type cast aluminum. The 290 low-compression engine (9:1) used the conformatic type, which employed a cast-in steel ring below the ring belt. This was the same type and diameter of piston that was used in the outgoing six-cylinder engine.
The 343-cubic-inch engines and the 290 high-compression version used the autothermic type piston. Since these two versions required completely new tooling, AMC invested in both designs. The final decision was made because, for these engines, a slight weight advantage was found with the autothermic type.
The development of both pistons was not without trials. The goal of every piston design is to achieve the required strength and longevity with a minimum weight, thus keeping the bearing loads and balance requirements to a minimum. Early failures occurred in the skirt, at the pin boss area, and at the balance pad. The correction partly consisted of a judicious shift of material from non-critical to critical areas, elimination of sharp corner stress risers, and changes in the re-enforcement ribs. In addition, it was found beneficial to move the piston sidewalls closer to the rod. This change provided a more rigid support for the pin, thus minimizing pin deflection and the piston boss stresses that result from such deflections. All of the piston changes required extensive dynamometer load testing before final design approval could be reached.
The piston skirt contour was developed from tests for cold scuffing, hot scuffing, full-throttle endurance, and from piston-noise evaluation on cold engines. The final elliptical contour drop at 45 degrees from center was 0.0152 +/- 0.001 on diameter for the 3.75 inch piston, and 0.0174 +/- 0.001 for the 4.08 inch piston.
A large portion of the development time was devoted to testing piston rings to provide the required oil control. Specifications established by AMC were to obtain a minimum of 1,200 miles per quart of oil during the initial break-in period. After that, oil consumption was to be compatible with the 4,000-mile drain interval. Consumption was not to be less than 1,000 miles per quart at 50,000 miles.
Both engines used 5/64-inch width compression rings and 3/16-inch oil-control rings. The top ring on the 290 was a straight face twist type, molybdenum-filled design. The 343 used a moly-filled, barrel-faced ring package. In the normal operating range below 4,000 rpm, at wide-open throttle, the blow-by was less than 2.5 cfm, which was considered very good.
The connecting rods on all of the Typhoon engines were constructed from the same cast malleable iron that the crankshaft was constructed from.
The cylinder head was designed to not only take advantage of modern manufacturing techniques but advances in fuel technology.
Excellent volumetric efficiency along with good octane tolerance were the protocols that were established. To this end, a wedge-type combustion chamber with a modified squish region was used.
This configuration is known for high rates of charge motion as the piston nears TDC and the resultant rapid flame expansion that not only limits detonation, but allows the cylinder pressure to peak sooner in the crankshaft's rotation past TDC.
Generous valve sizes of 1.787/1.406 inches, intake and exhaust, respectively, for the 290 engine, and 2.000/1.625 inches, intake and exhaust, respectively, on the 343 were employed. The valves were inclined at 18 degrees to the bore center to produce a good flow path to the cylinder. Individually supported rocker arms were actuated by pushrods through hydraulic valve lifters.
The cylinder head was made from a fine-grain cast iron and used oil-sand cores. Considerable analytical work was done to decide on the valve placement and the spark-plug location. The goal was for smooth combustion while maintaining good emissions control. Initial tests of the engine indicated excessive valve seat run-out, which was predominantly toward the exhaust outlet side. After deflection tests and stress analysis techniques were applied it was determined that changes in radii, stiffening of the deck, and the addition of supporting pedestals should be made. These changes were incorporated into the final design.
The camshaft was cast using super-Proferall high-chrome content iron. The original design called for lubriting of the cam lobes, but subsequent tests revealed that if the tappet face was lubrited, the cam lobe did not require it. The cam lobes were flame hardened to a Rockwell C 52 minimum and ground to a finish of 15 RMS.
The lubrication of the rocker arm was obtained from the tappet through a metered bleed and carried through the hollow pushrod.
Because the pushrod was guided by cylinder head slots at the upper end to hold the rocker arm in alignment, the push rod tube was cyanide hardened. No problem of wear from rubbing was encountered.
The rocker arm pivot ball was bottomed onto a shouldered stud so that it wasn't adjustable.
Valve stem oil control was accomplished by a nylon umbrella fastened to the valve spring retainer. The retainer was hardened and the spring contact face was machined at a five degree angle. It was found that improved valve rotation characteristics existed with the angled face.
The Typhoon family of engines was to be introduced with both two- and four-barrel carburetors. The 290 had a two-barrel carburetor that flowed 290 cfm, and a four-barrel carburetor that flowed 370 cfm. The 343 was only offered with a four-barrel and that carburetor was larger and tested to be 430 cfm.
The development of the new AMC engine was a complex program that required simultaneous studies so that optimum performance and service life could be obtained. The initial program began with seven engines, which were tested in both cars and on dynamometers. The data obtained from these tests allowed the engineers to formalize the design of major components, and many more engines were then built so that all of the necessary studies could be performed. Prior to 1967 production of the engine, 23,000 dynamometer hours and 2,500,000 vehicle miles on 125 engines were accumulated. The work was done as a combined effort of both the Detroit and Kenosha engineering groups.
Extensive road endurance tests were executed in all areas of the country to fully evaluate the Typhoon engines under different conditions. This included 14 engines which were tested for a total of 750,000 miles near San Antonio, Texas, on a route selected to provide 35 percent of the mileage at 70 mph during highway operation, 29 percent on a high-speed track at a sustained 80 mph, with the remaining 36 percent on unpaved farm roads, through hill country and cities and towns. One of the primary reasons for this program was to evaluate oil consumption trends under average customer driving conditions. Engines at the completion of 50,000 miles on this route were maintaining consumption figures of greater than 1,200 miles per quart.
In addition, a substantial power increase over the previous engines was accomplished. The two-barrel 290 developed 200 horsepower, while the four-barrel 10:1 compression ratio version pumped out 225 horsepower. The 343 developed 235 and 280 horsepower in its two configurations. When compared to the 1966 Ambassador model with a 327-cu.in. V-8, the 0-60 mph time was reduced one complete second to 10.0.
Though the public embraced the new engines with gusto, the AMC edict of "built-in quality through engineering" was never fully recognized by automotive journalists or car buyers. Though beauty is in the eye of the beholder, AMC products were never considered in the same social league as the vehicles from the other Detroit manufacturers, especially those from Ford and General Motors. This was a shame because the one auto company that took the name of our great nation offered some of the finest cars and engines the world has ever seen. A mechanical marvel if there ever was one.
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This article originally appeared in the March, 2007 issue of Hemmings Classic Car.
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