Quote:
Originally Posted by PONTIAC-ONE
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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These are simply advertised horsepower ratings that you must take with a grain of salt.
Quite often the top rating is not to exceed 10 pounds of vehicle weight per HP. Note the Firebird vs GTO ratings for the same exact engine, Firebird being lower because of the lower vehicle weight.
Lastly, HP isn't always dependent on cubic inches. A 428 could have more peak HP, but the 455 would have more torque.
Again, some of the ratings are closer to 'real world' than others.
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One fun comparison - Do you think a 370 HP '69 -'70 RAIV 400 is equal to a 370 HP '64 421 HO in true HP output?
My money's on the RAIV, out-powering the 421 HO by at least 50 HP. Restored RAIV 400 engines have seen 425 HP on a dyno.
As much as I love my '64 421 HO I doubt it can make the factory stated 370 HP, 350 might be more realistic but who knows.