Additional Comparisons of US V8 Engines
'55 Chevrolet V8: 575 lbs. -head bolts and pressed in rocker studs penetrate water jacket, the two lifter galleries feed off the rear cam bearing groove along with the rear main: somewhat prioritized but not quite. It does appear that the 'short' style Chevy small block valve cover stamping may help oil the rocker tips by oil squirt deflection. Oil pump pickup tube needs a bolted tab to hold it on securely. Chevrolet did make internally balanced forged piston forged steel crank and rod versions of this engine in a variety of displacements which indeed makes the task of building one into a proper racing engine much easier if so equipped. Another design feature is seen by comparing total piston length to to total cylinder wall length of this engine to these other cut away veiws (note cylinder wall length is only 1/3rd longer than piston length) SBC's low deck/short stroke/big bore design was rather unique and it may be argued that this design peaked with '69 302 Z28 engine showing superb high rpm capability...
'66 290-401 AMC V8, 540 lbs. (generic weight) -Scan taken from '71 AMC Technical Service Manual, appears to be '68-'69 "AMX 390" having '66-'69 type concave floor rectangular outlet exhaust ports -quickly re-designed for '70 models to have better flowing convex floors; aka 'dog leg' heads.
Where 'time is money', this design adopted lower cost stamped steel rocker arms which, along with fewer drilled oil system passageways, increased speed of manufacturing and features simple wedge combustion chambers to meet new US Federal Emission Control Laws which basically outlawed the former AM Rambler V8 combustion chamber design. Lower cost/faster production speed cast nodular iron replaced more expensive forged steel crankshaft and connecting rods in the smaller 'bread and butter' versions of this engine
Notice the 'extra meat' around the crank gallery at oil pan flange for strength & rigidity compared to Chevy above.
Truth is, architecture of '66-'91 AMC V8 is near copy of Buick's '61 V8 design.
Cadillac also copied Buick's '61 oil-pump-in-the-aluminum-timing-chain-cover design when they revised their '53-'62 version of the '49 OHV V8 design in '63 for weight reduction. (revised 599 lb. Cad V8 then matched Rambler V8's 601 lb. rating)
The stock curved top AMC valve covers positively deflect oil squirts from the push rods to lube the rocker arm and valve stem tips.
It may be observed that all US automakers were doing a similar thing in the later half of the 1960s; all the 'bread and butter' engines were getting revised to have longer strokes, lower compression and simple 'wedge' style combustion chambers, a combination that is known to produce less toxic oxides of nitrogen exhaust emission content.
It's not that short stroke, big bore, high compression designs became outdated, rather it was the emission content of their exhaust that became illegal.
AMC published a paper bound book in '72 named "Performance American Style" which describes how to modify their inline sixes and vee eights in three sections for racing purposes, each section describes the general components needed to suit an expected rpm range.
Without exception, all 390 and 401 CID versions of this engine came with superior quality high strength forged steel connecting rods and crankshaft.
Although one AMC engineer was quoted in a magazine interview for saying "AMX 390"'s rotating parts were designed for 8000 rpm, none of these '66-'91 AM V8s came from the factory with internal balanced rotating assembly; they were all external balanced to reduce production cost and increase speed of assembly.