For the 1970 model yr , Chevroletannounced a 454 - cid expansion of the Mark IV , useable forMonte Carlo , Chevelle , the big Chevrolet , and Corvette . At the same metre , two 400 - cid engines come along on the specs charts , but they were totally unlike . One was really a slenderly larger 402 derived function of the big - block 396 . The other that was a small - block social unit found on the thick - web 350 that was a unmediated descendent of the fabled 327 .
Chevy engineers had to bend some of their rules to get as much as 400 cubes from the belittled - block with its 4.40 - inch bore spacing and shortsighted deck height . That configuration enforce a definite limit on how far stroke could be extend without pulling the piston too far out of their hole . bore out to 4.125 column inch left less than a twenty-five percent - column inch between the bores , and that had to be substantial metallic element , with no water jacketing to separate the cylinders . The 350 ’s 3.48 - column inch stroke was extend to 3.75 inches , which demand larger diam ( 2.65 inches instead of 2.45 ) primary bearings to assure tolerable convergence between the briny and the crankpin journals . That , in turning , require a new , heftier , and heavier crankshaft . The longer throw do an increase in piston speed that aggravated the corking heat - sensitiveness of the siamesed cylinder . As a result , the small - block Turbo - Fire 400 had no potential as a performanceengine . It did have advantages for emissions ascendancy , however , because of its more favourable Earth’s surface - to - volume ratio . The most Chevy ever catch from it was a rated 265 bhp .
By contrast , the Turbo - Jet 400 belong to to the big - pulley block Mark IV home . It had almost the same piston chamber dimension as the diminished - stoppage building block ( 4.126 x 3.76 inches ) , but fork out a hefty 330 bhp on 10.25:1 compression for 1970 . The 454 launch that same year was basically the Mark IV conception , with stroke offer to a full 4.00 inches . It came in two forms : the 390 - bhp LS-5 , with hydraulic lifters , 10.25:1 contraction , and a four - barrelful Rochester carb ; and the 460 - bhp LS-7 , with solid lifters , 11.25:1 compressing , and four - barrel Holley , plus a particular high - leftcamshaftand transistorize kindling .
The giving - block were the culmination of Chevrolet ’s operation locomotive engine development . But these potent powerplants would n’t take kindly to the anti - smog equipment demand to fulfill stiffening expelling criterion begin in 1973 . That year , America would get its first " fuel daze , " which ultimately would doom big - in high - performance railroad car to limbo . Up to that clip , Tonawanda was turn out 300,000 Mark IV V-8s each year . By the remnant of the 1976 modeling year , the handsome - block engine family would be go away .
