454 piston question
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Melting Slicks
Joined: Sep 2007
Posts: 2,387
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From: CA.
454 piston question
my last vet was a 70 with a 454 with 390 hp. now i got a 72 454 with 270 hp. i read 70 was more hp because it was measured motor only without pullys or anything and 72s are measured at wheels. when i did my 70 over it had domed pistons. does the 72 have same and is 72 a 4 bolt main also/ thanks.
Melting Slicks
Joined: Nov 2004
Posts: 2,672
Likes: 6
From: Nevada City California
1970 engines were measured "gross horsepower" meaning they were rated with no accessories. 1972 engines were measured with all accessories attached including exhaust manifolds. GM referred to this as "net rating" as installed in car. This rating was at the flywheel...not measured at the rear wheels.
1970 engines were the last to use a domed shaped piston for compression. 1972 LS5 engines use a flat top style. 1972 3999289 casting blocks used for LS5 applications were 2 bolt main configuration.
1970 engines were the last to use a domed shaped piston for compression. 1972 LS5 engines use a flat top style. 1972 3999289 casting blocks used for LS5 applications were 2 bolt main configuration.
Melting Slicks
Joined: Nov 2004
Posts: 2,672
Likes: 6
From: Nevada City California
I wouldn't necessarily refer to it as weaker, its internal components are the same as a '70, with the exception of recontoured pistons and reconfigured heads now with open chamber design.
This is what lowered the compression of the '70 engine of 10.25 to 1 to 8.5 to 1 in '72.
The '72 LS5 horsepower net rating of 270hp is slightly down from '71, which had a similar net rating of 285hp. So the "gross equivalent" to '70's 390hp would be 350hp. Most people would quote the '71 365hp gross figure, but this is incorrect since '71 LS5's did not use the A.I.R emissions system in conjunction with the TCS system as the '72's did. There was also a recalibration of the distributor and carburetor that led to the additional horsepower reduction.
This is what lowered the compression of the '70 engine of 10.25 to 1 to 8.5 to 1 in '72.
The '72 LS5 horsepower net rating of 270hp is slightly down from '71, which had a similar net rating of 285hp. So the "gross equivalent" to '70's 390hp would be 350hp. Most people would quote the '71 365hp gross figure, but this is incorrect since '71 LS5's did not use the A.I.R emissions system in conjunction with the TCS system as the '72's did. There was also a recalibration of the distributor and carburetor that led to the additional horsepower reduction.
