A while back I started asking questions about limitations of the factory iron block looking to find ways to give it the best chance to survival.
https://forums.maxperformanceinc.com...d.php?t=830317
http://www.pontiaczone.com/forum/showthread.php?t=31850
I was very interested in finding learning if there was a coloration between the rotational weights and mean piston speeds of failed blocks... because I just find it hard to believe 750hp is the magic limitation... The block must contain the Rotational weights @ RPM... So for the best chance at longevity... keep both those numbers low and cross your fingers.
The old school Pontiac guys on PY and other forums shared their experience and predictions to the point I started to doubt the long term reliability over the 750hp threshold. Could it be done, YES, but for how long was always the question with no real answers pertaining to rotational weights @ RPM. Simply questioning that 750hp threshold sparked anger in a great many people... This is how passionate some are on the topic...while I never said they where wrong, I just questioned the what, why how... which they where unable to fully articulate other than it just is. This made asking the questions on this very topic a bit aggravating to me because I thought there would be more specific answers.
In the end, what I got was that the factory iron blocks are inconsistent in their strength... So even trying to collect information on rotational weights and RPMs would lead to no usable data. So while some blocks will survive at 1000hp, others will crack down the middle at 600hp.
With all that said, most of these people who have responded have MUCH MUCH more experience than I have with 455 blocks so I ended up heeding their collective advice and just sacrificed my first born for an MR1/ 3.25" mains. Now instead of the original 10-15psi goal, its now 15-20psi.
Sorry the long winded response.... basically I asked the same question and left with no real answers except Keep the RPMs down... 5500 seemed to be as high as you should go as far as RPMs are concerned... Lower will be better... it will last forever at idle.
SPEED SAFE, NICK