69 428 made 390 hp
70 455 made 370 hp
Is this fairly accurate? 428 had a little more compression but I would think the 455 would out power the smaller engine....
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 2 sons, 2 Firebirds. 1971 Formula 455, 1972/w 455 HO added.
1974 Formula 400 "retired", parts car now. 
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