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				03-05-2020, 04:05 PM
			
			
			
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			 So how much horse power did a 1969 427 ZL-1 engine make? It depended on how you measured it. The following are dyno results with a max RPM of 6750: 
 375.7 HP - as delivered in a 1969 Camaro with 36 degrees timing and chambered exhaust
 
 418.9 HP - same as above but replace cast iron exhaust manifolds with 2-1/8" headers
 
 447.2 HP - same as above and remove air cleaner, A.I.R. pump and alternator
 
 523.6 HP - same as above and remove chambered exhaust - run open headers
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