A stroker 400 /= a 455. While the cubic inches become nominally the same, the differences in bore size is enough that the two engines do make power a little differently.
A stroked 400 using the standard 4.25" stroke ends up being pretty under square with a nominal +0.030 overbore. On the other hand a 455 if using it's factory 4.21" stroke, starts to move towards square as the engine has over bore's done. A +0.060 bore 455 with the factory stroke becomes square. As a result the 455 may tend to make a bit more power, later in the rpm band vs a stroked 400.
The other thing to keep in mind about the differences are the main sizes. The 400 block will have a 3" main while the 455 carries a 3.25" main. The larger main in the 455 does carry load better than the smaller 3" main 400 blocks, but you have to contend with higher bearing speeds and subsequent oil heating and pressure requirements, as a result.
As mentioned already, you want to stay away from 400 blocks with the 577 end casting numbers.
My +0.040 455 makes peak torque at 4700 rpm and peak HP at 5800 rpm with a 240/248 on 112 cam. You can see it wants to make power a bit later than a typical 460+ inch Pontiac. It still makes over 500 ft lbs well below 3000 rpm though.
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-Jason
1969 Pontiac Firebird
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