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I have noticed that from 1970 to 1975 the 454 specification are very similar. they all have the same bore, stroke, mains, rods, and valves dimentions. The cranks from 70-72 are forged steel and from 73-74 the are nodular (what is that). The heads vary a little with (73-74 having 113 cc heads), (72 113 cc's), (71 118 cc for the 425 hp, and 113 for the 71 365 hp motor), Since most of the specs are similar does that mean the HP diferances are primarily due to cams.
The changes in advertised ratings from 1970-1974 on essentially the same 454 engine were a result of compression ratio differences (pistons) and the change from the SAE Gross HP rating method to the SAE Net method. The "nodular" crank is a high-grade iron casting (vs. the steel forging used in other applications).
My first Corvette was a full option '73 454. What I could never quite understand is the '73 LS4 was rated at 275 hp as compared to the '72 LS5 @ 270 (and I think the '74 LS4 was also rated at 270 hp), because Exhaust Gas Recirculation was introduced on the '73 and that in itself had a negative effect on horsepower and to some extent on drivability. So why did the hp go up in '73 by 5 only to drop 5 in '74 with the same engine? PR? I also THINK the cam was retarded a couple of degrees sometime after 1970.
Mike
1970 LS-5 454 would be the last year of high compression style piston and closed chamber style head.
1971-1972 LS-5 454 would be very similar, lower compression style piston and open chamber style head with some confusion arising from a difference in net horsepower ratings. 285hp for '71 and 270hp for '72.
1971 LS-6 is an entirely different breed of animal, can't really compare with '70 thru '72 LS-5's.
1973 & 1974 LS-4 454's were generally the same, and engine internals were downgraded a bit in performance enhancements. The 275hp vs 270hp is an interesting anomaly though.
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