Super Stock and Drag Illustrated magazine, August 1972

Parts And Pieces From AMC in order to build any of the V8 AMC engines, from the 290 to the 401, for performance use, you.ve got to know about family.s and interchangeability. Here it is, folks.

THERE ARE A LOT OF performance enthusiasts running around today with heads full of wrong ideas about American Motors cars and engines. The general opinion is that they are not suitable for performance or racing use, and that opinion is about as far from the truth as an opinion can be. The popularity of these machines is only now starting a period of deserved growth, but the pieces have been there all along, never receiving any real attention from large numbers of builders, though quite capable of impressive performances and incredible longevity. The fact is, inch for inch and pound for pound, the American Motors

V8 engines are among the best available for durability and performance.

Like any engine, the AMC V8 can be made to perform with an investment of money, time, and planning, using many stock parts and a few items from the unfortunately limited supply in the performance aftermarket. With the help of AMC.s Performance Activities Department, we have compiled the information necessary to build up AMC V8 engines for street and drag strip use, and we.ll try to present it in a clear and orderly fashion, with as many alternatives for the builder as possible, a few no-no's, and some definite recommendations for the engine-building process.

All recent AMC engines are very light, using aluminum covers, thinwall castings, lightweight power accessories, while developing good power and superior flow.

BLOCKS

Selection of a block will depend on what the AMC builder has to start with, the ultimate purpose for the car (class, brackets, street, Modified, SS, or Stock), and the money available for completion of the project. We.ll restrict all of our engine discussions to .68 and later engines, from 290 cubic inches on up. In order of size, there are the 290, 304, 343, 360, 390, and 401 V8 engines in the .68 to '72 lineup. Taking the engines as groups or families, the 290 and 343 form a group, with 3.75" bore and 3.28" stroke for the 290, and a 4.08" bore and 3.28" stroke for the 343. Obviously, the 343 is a 290 with an increase of .33" in the bore. The next family is formed by the enlarged versions of the previous two engines, the 304 and 360 blocks. The 3.75" and 4.08" bore remained the same, and stroke was increased by .160" to 3.44" in both engines. The 390 engine is by itself at 4.165" and 3.574" bore and stroke, and the 401 measures 4.165" by 3.68". The engines are further separated in other respects, in that engines up to 1969 were made with one block deck height, and 1970-72 engines used another deck height. This presents problems when heads and manifolds are installed, and we'll get into that later. Another basic block item to note is that 290-304-343-360 blocks are made for use with cranks having rod journal sizes of 2.09" while 390 and 401 blocks use 2.248" rod journals. Main bearing journals and bore centers on all AMC V8 engines are exactly the same at 2.747" and 4.75", respectively. For maximum performance, we would recommend using the 401, even though it will cost, since it.s the largest and will fit the same way as the baby 290.

For drag racing use, any of the V8 engine blocks can be expected to deliver performance and longevity. They.re all thinwall castings, light and strong, and they.ll accept heavy modifications short of supercharging and fuel with no problems. For the cautious, though, the 390-401 blocks are indicated, since they have more than twice as much beef in the main bearing area, and can all be machined to accept four-bolt main bearings caps from an outside supplier such as Milodon or Summers Brothers (1970 and later blocks only).

Maximum overbore recommendation for 290-304 engines is 3.830", the 343-360 is 4.160", and the 390-401 series can be punched to a maximum of 4.1875". Cylinder bore finish should be set to 30-40 micro inches, which is a step rougher than the factory 20-30 micro inch finish, and the cross-hatch angle in the bores should be between 45 and 60 degrees. Of course, any block being modified for racing or increased performance should be cleaned thoroughly with detergent and water about four times, blown dry with an air hose, and carefully inspected for cracks. All remaining casting flash should be buzzed off with a highspeed hand grinder, with special attention to the lifter galley area. All sharp corners should be broken with a heavy-duty file to reduce heat and stress buildup, and the extremely generous lifter bores should be honed out for free travel. It.s also a good idea to open up the main oil passages in the block to increase flow through the engine.

BOTTOM END

In discussing bottom end pieces, once again, "families" must be explained. As noted earlier, all AMC V8 cranks have 2.747" main journals, while engines to and including the 360 use small rod journals of 2.09" diameter and the 390 and 401 use 2.248" rod journals. The 290-360 cranks are nodular iron cast units, while 390 and 401 cranks are forged steel and stronger by far than the cast ones. However, drag racing engines of 290-360 cubic inches can use the stock cranks if they are properly magnaflux checked, cross-drilled for oiling, and treated to a Tufftride and polish job by competent crankshaft specialists. In either case, cast or forged, crankshafts should be chosen carefully, checked for straightness and index, and handled by machinists who know what they are doing.

When it comes to building an AMC engine of specific displacement, the whole problem of mating blocks to cranks, rods, pistons, and pins will have to be dealt with, and there are important differences in size and quality in all of these components. The small 290-360 rods use 2.09" big ends, with .931" pin bores and pin lengths of 3.187". These 290-360 rods are all 5.875" long, and they were all made of cast iron, which means that they can only accept so much stress, even after magnaflux inspection, shot-peening, and polishing. Early (.68-.69) 390 rods had a big end diameter of 2.248" but were only 5.790" long. Late 390 and all 401 connecting rods use 2.248" crank diameters, 1.00" pin bores, 2.94" pin lengths, and center-to-center lengths of 5.858", and all 390-401 con rods are forged steel and recommended for performance work after sizing, Magnafluxing, shot-peening, and polishing. Factory recommended clearances for racing engines are .0065-.009" piston-to-wall, for forged pistons.012-.017" ring end gap, .012-.016" rod side clearance, 0025-.003" main bearing clearance, .002-.0025" rod bearing clearance, and .080-.100" piston-to-valve clearance in all cases.

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TOP - Modern high-flowing heads use what.s called a dog-leg exhaust port, and no other AMC head will flow half as well, race-bred or not. The dog-leg heads will go right on to 70-up engines, but need a special dowel setup for use on earlier engines.

SECOND - Intake ports on late AMC heads are large and fast, and a good professional porting job will yield great increases in flow and performance when done with a proper valve job and milling.

ABOVE - Late model (.70-up) big blocks have twice as much main bearing web beef, will accept 4-bolt mains like these.

LEFT - Late heads have 2.02" intake and 1.625" exhaust valves.

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RIGHT- Cutaway shows typical construction of an AMC Dana rear, which uses a ring gear of 8.9" diameter, hefty pinion, and small ring width. Axles can be used for mild racing if they are machined for new longer and wider keys, but aftermarket billet axles are best for serious racing use. Ration selection is very good.

BELOW RIGHT - Late model 401 crankshaft is forged, as are late 390 units, and both are okay for racing if they.re properly treated before installing. Cast cranks for small engines will also take a lot of abuse.

RIGHT - Connecting rods for the AMC engines belong to three basic families, with 5.875" rods for 290-300 engines, 5.790" rods for '68 and .89 390 engines, and 5.850" rods of forged steel for late 390 and 401 engines. As family changes, the size of the big end bore and the pin bore also changes.

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Pistons for American Motors V8 engines are a problem. The factory does not engage, like some others, in producing or having produced oversized, extra-compression pistons for owner or dealer installation, so that, other than the aftermarket, where JE Engineering and Venolia offer special forged racing pistons for pretty good prices, the plan is to use the highest compression piston offered for any of the six engines under discussion, with the appropriate matching small-cc-displacement heads and big valves. Following this plan, the 290 engine' would use the .69 10:1 4-barrel piston. The 304 would take the .70 model year 9:1 unit. The 343 engine could best use the 1969 10.2:1 4-barrel piston that was used with 51 cc heads. The highest compression piston ever used in the 360 engine was the .70 290 hp 4-barrel model, and the old standby 390 should use the 1970 325 hp 10.2:1 pistons (because of severely limited supplies, we will not include in this story any mention of Rambler SC/Rambler, Rebel Machine, Hurst SS/C .69 AMX, or Trans-Am Javelin engine parts for the various engines. Even if a source of supply could be found, prices for some of these pieces are astronomical). The new 401 engine will benefit most by installation of .71 330 hp, 9.5:1 pistons. Pistons for all engines should be properly machined and fitted with recommended clearances. The factory recommends conversion of rods to full-floating configuration in heavy duty applications, with .0008-.0012" pin to con rod clearance, and .0007-.0010" pin to piston clearance. Oiling holes should be drilled on the small ends, and the piston pin bores must be grooved to accept pin locks such as Tru-Arc rings.

CYLINDER HEADS

Once the builder has opted for a block and bottom end assembly, head selection is the next big decision, and it.s a complicated one. The various combinations of chamber cc volume, port configuration, and valve sizes in AMC V8 engines between 1968 and 1972 can cause a great deal of confusion.

Basically, the 290 and 304 engines used small valves, with 1.787" intake and 1.406" exhaust head diameters. The 343 engines, the .70 model 360, and the '68-.69 390 had intermediate valving, with 2.02" intakes and 1.625" exhausts, but .70 and later 360, 390, and 401 blocks used the big 2.02" in-takes with larger 1.68" exhaust valves. So far, so good. The problem is that the only heads that really flow well are the later "dog-leg" exhaust port models with convex port floors, as opposed to the earlier .68-.69 rectangular exhaust port heads with concave floors. The 'dog-leg' heads flow a full 50% more fuel/air charge than the older heads, and these are the ones used by the AMC Pro Stock fleet.

The hot set-up then, in cylinder heads, is a dog-leg exhaust port head, with the small 51 cc chamber used in pre-smog years, and with the larger intake and exhaust valves, right?

The problem is that there is no one cylinder head with all three features. Now, the Performance Activities department tells us that the rectangular exhaust port heads are not the hot tip under any circumstances, since they won.t flow as well as a dog-leg setup even when they.ve been ported and polished. Three choices remain. The 1970 360-390 head (3916291) having the 51 cc chambers, dog-leg porting, and intermediate valves (2.02" and 1.625") is a good bet, but you will have to resort to junkyards or hoarders, since they are not a service replacement item any longer. If you can locate them, bore out the exhaust valve seat to accept the 1.68" exhaust valve, and you.ve got all three features in one set of heads. Of the parts available through AMC service, the 1970 304 head (4487242) has 51 cc chambers, dog-leg ports, and small valves, which can be replaced by big valves fairly easily. The added attraction of the 304 head is that it.s available as a new replacement part at the dealerships at a reasonable price. If you are willing to go the aftermarket route for high compression pistons, the next best choice is the low-compression 58 cc .71-.72 360-401 head. It has dog-leg ports, the biggest valves available, and easy access through normal parts channels. Its part number is 8120126.

Performance Activities has developed a complete plan for head modifications that work and produce gobs of power. It.s not simple, and it must be followed to the letter to get maximum gains. It starts with a spotfacing operation on intake seats with a 2.40" cutter that has a 45º by.12" chamber, to get a 2.16" diameter at the outside edge (these and all other modifications are for use with production large valves, 2.02" intake and 1.68" exhaust).

When the spotfacing is finished, the intake ports get a new throat bored into them, 1.815" in diameter and half an inch deep as measured from the spotface. The exhaust seat then gets a similar spoffacing using a 2.06" cutter with a 45º x.12" chamfer to get a diameter of 1.82" at the end of the chamfer. Both spotfaces should then be blended into the rest of the chamber with round file and emery cloth.

The intake port then gets more attention, using a 45º cut out to 1.99" outside diameter, followed by a 60º grind to 1.94" seat ID. Then a 40º cutter is used to the extent that the 40º and 60º portions are the same width. The valve guide boss is then blended to .040" from the guide hole. Engineers caution that no metal should be removed from the inlet end of the port up to the point where the turn starts toward the throat, with the exception of casting flaws. Grinding at the turn should be done only as required to blend to the throat to .10" minimum throat length. All remaining sharp edges should then be blended.

Exhaust ports in the heads get their own treatment, starting with a 45º seat ground to 1.64" outside diameter. A 60º cutter is then used to intersect the seat at a diameter of 1.570". A throat radius of .730" is then ground to the center of the valve guide but only for 180º of the circle, and placed in the direction of exhaust gas flow. The throat is then blended to the port and then end of the valve guide is likewise blended.

The basic shape and size of both intake and exhaust ports should not be changed except as necessary to match manifolds. The exhaust manifold port widths for these engines are made wider than the ports in the heads to allow for thermal expansion. When the big heads are used on 290-304 engines, the bores in the block must be top-chamfered to clear valves, and in all cases the valve seat spotfaces should be checked for interference with headgaskets.

The valves themselves should be modified to take full advantage of the new, smoother ports. Intake valves should be ground with a 45' face starting at.045" outside the land length. The inside edge of the face should then be ground at 20º to a 1.930" inside face diameter (face width should be .075"). Exhaust valves have their inside face edges ground at 18º to a,1.55" inside face diameter (face width is.085").

Keep in mind that the aim of the information in this story is increased street performance from basically stock engines ang parts. Any serious attempt at building an AMC car for NHRA class competition in Stock or Super Stock requires consultation with NHRA technical staff people and with AMC.s Performance

Activities Department before starting out. We offer the information in this story as a guideline for street and bracket machinery, for which there are virtually no rules.

CAMSHAFTS AND VALVE TRAIN

Visually all modern-times AMC engines, Sixes and V8.s alike, have used hydraulic camshafts, and all V8 engine cams use the same bearing journal diameters, so that they all will interchange from engine to engine. The trouble is that all of the standard V8 grinds are gentle as pussycats and are combined with soft springs and spongy lifters. The single option available is the dealer-installed kit, 4488413, for .70-.72 engines only (tlute early kit, 4486719, for low-block V8 engines, is no longer available through the dealer network). The 4488413 kit contains everything in the valve train, and the grind is a 302º-302º, 98º overlap, .477" lift profile. It.s plenty sufficient (with headers) to pep up a stock engine, but there are so many aftermarket grinds available (see separate listings of aftermarket parts) at better prices that the factory cam kit pales in comparison. As far as swapping stock cams from one engine into another, simply because they fit, there.s very little to be gained.

When using aftermarket cams and valve train pieces, follow installation instructions from the manufacturer, setting springs for heights and pressures to specs, and d8-greeing the cam at whatever position is recommended. Without changing valve sizes or weights from stock, it will be possible to pick up about

2500 rpm on top with almost any grinder.s cam and kit pieces, and the inclusion of aluminum roller-tip rockers will boost rpm even more, though they are pretty expensive items for street use.

INDUCTION SYSTEMS

In this area, there are again the 'families' to deal with. All 1966-69 intake mani-folds will interchange with each other, since block and head castings and bolt patterns were all the same regardless of displacement, so that 'instant four-barrel' modifications can be made easy. Likewise, the .70-.72 manifolds are all the same, but because the two center mounting bolt locations have been moved upward and inward, the late manifolds won.t fit on early blocks and vice versa. Either way, all production 2- and 4-barrel manifolds are cast iron and fairly efficient.

AMC dealers do have a small selection of manifolds to sell, though, and the most popular one is the 3199763 for .70-'72 engines. It.s a dual plane cast iron manifold that.s good to 6500 rpm, with boost over carburetor bolt patterns. For earlier engines, the Edelbrock R4B is recommended by the factory. The most radical factory manifold available is the aluminum dual-quad cross-ram for twin Holleys, under number 4486228 for early engines, and 4488411 for .70-.72 engines. It.s not the easiest system in the world to cope with at low street speeds, but it.s great on the top end, from 7000 to 7500 rpm. This manifold was commissioned by AMC through Edelbrock and also carries Edelbrock part numbers STR-11 for early engines and STR-11-70 for .70 and newer engines. The cross-ram should be used with twin 600 or 700 cfm Holley double pumper carburetors. The recommendation for either the factory or Edelbrock R4B single-quad manifolds is either the 780 cfm vacuum secondary carb or the 800 cfm double-pumper. Stock carburetion on early V8 engines from AMC consisted of Carter WCD 2-barrels and AFB 4-barrels with 1.44" primary and 1.69" secondary barrels. In 1970, the corporation switched over to the Ford Autolite 4300 model 4-barrel with 1.56" primaries and 1.69" secondaries, and while this carburetor is not as widely favored as some others, it can be made to work with the normal rejetting, float-setting, and pump-arm modifications.

As a fillip item for use with trick mani-folds, American Motors does stock a heat-blocked manifold gasket that also acts as a hot oil baffle over the lifter galley. The three-piece set includes front and rear seals and goes under number 4488475 for engines to 1969, and 4488476 for .70 and later engines. It.s a small item but worth including on any hot street engine.

IGNITION

Standard factory ignition systems for most recent V8 engines include single-point distributors with vacuum advance, 12-volt negative ground supply systems, and alternators. Spark plug cables are carbon-core, and Champion N12Y spark plugs are installed at the factory. For high rpm consistency, the factory parts system once included a Delco capacitive discharge ignition, 4485742, including distributor, heat sink, coil, and wire harness, but it has officially been discontinued and removed from the system, though there may be a few floating around. The optional ignition system that remains is a Mallory dual-point unit with coil, ballast resistor, and switch, carrying part number 4487900 for an ordinary unit, and 4487901 for the distributor with mechanical tach drive. The factory recommendation is 38-42º total advance, all in at about 2800 rpm. Naturally, the carbon core wire should be discarded in favor of one of the aftermarket brands with heat resistant coating and solid copper or steel cores. Low budget AMC builders could retain the stock distributor, disconnect the vacuum advance system, install heavily sprung points, and replace the wiring and coil, but it.s far simpler to install a complete, integrated system such as the AMC/ Mallory or other high performance ignition.

DRIVELINE

The 10 1/2" Borg & Beck clutch is standard equipment on AMC machinery, and spring loads range from 2000-2500 lb. The 304 clutch has generally used a 9-coil setup, while the 360 and 390 have used 12 coils and three rollers, and the newer 360 and 390 have used 12 coils and three rollers, and the newer 360 and 401 engines use 12 coils and six rollers. This last one is the unit recommended for limited performance work by the factory racing people, since it has an upper limit spring rate of almost 2600 pounds. But the factory recommends any of the popular 10./2" B&B aftermarket replacements, and a spring loading around 3000-3200 pounds.

The Borg-Warner 4-speed transmission commonly known as the T-10 has been optional with AMC cars for many years, and two versions have been used. The close-ratio box, using 2.23, 1.77, 1.35, and 1:1 ratios is the more widely used, though in 1968, the wide ratio T-10-T was optional and is still available. Complete transmissions must be ordered from Borg-Warner, but gearsets alone can be had through AMC. It used ratios of 2.64, 2.10, 1.46, and 1:1. These two and all other versions of the T-10, including the aftermarket Super T-10 will bolt right up to the 4-speed bellhousings on any AMC V8 engine. Performance Activities told us that the '68-.69 T-10-V transmission used with 390 engines incorporated a larger front bearing cap (3185168) and a bigger throwout bearing (3190517) that should be installed on any later T-10 used for performance work. Final selection of ratios would naturally depend on rear ratio, tire size, car weight, and the extent of engine modifications, but there are so many B-W T-10 trans-missions around that there should be no problem in finding an ideal unit. Gremlins, which don.t come with 4-speeds behind their 304.s, will accept a T-10 if the Javelin/ AMX trans mount is used and the driveshaft is cut 1.280". The 4-speed bellhousing must-be used, though.

When it comes to automatic transmissions, all but 1972 AMC cars used a Borg-Warner three-speed with ratios of 2.40, 1.47 and 1:1, with 11" converters for 290 and 304 engines and 12" converters for 360, 390, and 401 engines. For 1972, the corporation switched over to Chrysler Torqueflite transmissions with standard 2.45, 1.45, and 1:1 ratios and a whole lot more good features and strength. The Chrysler-supplied transmissions use 10.75" converters for 304 engines and 11.75" units for 360 and 401 engines. The big hitch in converting an engine that used the Borg automatic over to the Chrysler is that the crankshafts must be changed to 1972 cranks with the proper flange thickness and hole patterns to accept the Torqueflite flex plate on the flange. The stock Borg transmission is flatly unacceptable for strenuous use, and the Chrysler is just about the best available, especially since the aftermarket is loaded with possibilities for shifters, converters, and valve bodies compatible with street and drag strip use. Once the '72 Torqueflite (AMC still calls it Torque Command) is installed, all that's needed is the '72 driveshaft for the particular body style, since the Chrysler trans is shorter overall than the Borg-Warner.

When it comes to rear end ratios, American Motors has one of the best option lists in the business, and they.re all built around the standard Dana rear with a basic 8.9" ring gear diameter. The 3.91 rear is 4485750; the 4.10 unit carries number 3208546; the 4.44 ring and pinion set is number 3209854; the 5.00:1 screamer is listed as 4486587. All of these rears and in fact all AMC rears from 2.37:1 on up are available with the four-pinion Twin-Grip option and they.re as near bulletproof as they can be without modification or substitution of aftermarket heat-treated ring and pinion sets. One of the parts that has been trimmed from the "available" list is the 4486997 Detroit Locker locking differential. It can't be had through normal AMC channels, but there are undoubtedly a few used ones around at American Motors specialty garages.

That, in a large nutshell, is the story on parts interchange possibilities, factory available pieces, dealer-installed options, and AMC recommendations on building relatively mild street and strip cars. We won.t get into suspension and accessories, since there are so many variables involved, but we have taken you through the entire engine and driveline and hopefully we.ve covered the basics. AMC's Performance Activities Department is busy right now on the preparation of a complete parts and procedures manual for all AMC cars and engines, and they.re opening up an information service (letters only, no phone calls, please) that will be invaluable to all AMC floggers. Direct all correspondence to AMC Performance Activities Department, 14250 Plymouth Road, Detroit, Mich. 48232, and be specific in your letter as to car, year, engine, trans, rear, class or intended use. After spending most of a week talking with the staff we know you'll get a prompt, accurate, and complete answer to your specific questions.