If you want the best answers you can get, post this on boards that have many more members that have been through this or that make 500rwhp or more... there are just not that many on here. Check out:
http://www.hardocre50.com and
http://www.turbomustangs.com
I have had freinds split blocks in TUNED car at 420rwhp... these cars were also run at the track every week though and they did last a while. Detonation, RPM, and power are what kill stock blocks. The main caps walk and distort. I have no personal experience on the girdles, I think the theory is good and I wouldn't build a stock block without one, but from all I have seen I am a believer in the "all they do is hold the two halfs together."
I have a friend that recently built an iron eagle dart block for his 500rwhp fox (its gone 10.1 at 13Xmph). He is also the one that split his stock block when he was making 420rwhp. I asked him his thoughts on building the dart shortblock and he told me that he personally might have done things differently in that for the money he has in his dart block 347 he could have split 5+ stock shortblocks.
I think that with a prolonged load as you will see in the silver state classic, you are more proan to see a failure than most would with 500rwhp in a stock block.
As for the new ford block... if you have the luxury of waiting for ford to release something then go for it, but don't expect to see anything anytime soon.
One thing to mention about the mexican, dart iron eagle, and R302 is that they are not setup for hydraulic lifters and you'll need to either machine the block to accept your stock lifter spider or buy the retrofit lifters that are ~$400 which adds greatly to the cost of these blocks. I don't know if the sportsman needs these... I don't believe it does.
One thing to remember as well is that its not neccessarily the amount of power that kills te block, but also the way that power is made. You'll see a lot of pure street guys make the switch to the dart blocks even though they add weight to the nose of the car and these guys typically make in the low-mid400 range NA, but they do it with a lot of RPM. A supercharger car is more likely to crack a block than a turbo car (assuming the tune id dead on for both) due to the added stress on the front of the crank from the belt AND th fact that the supercharged car must make more power than the turbo car to obtain the same power levels due to the fact that the supercharger requires power to turn the belt... this goes hand in hand that a turbo car doesn't require as large as a fuel system as a blower car given the same power levels.
If you build a stock block based setup, I wouldn't waist money on any high dollar (ie forged) internals.
I too have spoken with a few of the "bigger" named companies and they said that a stock block should be fine with 500 or less RWHP, but everyone else that I trust and have delt with and I concider "in the know" have all laughed at me when I even mentioned keeping the stock block in anything making decent power.
I REALLY like the dart sportsman and that is the route I'll be going in if I ever decide to truely step up to some big power. I need to check into the cam bearings for it though as they are different than stock bearings but I don't know how much, if any, added cost this will add to a dart sportsman based buildup.
Going to the dyno wed. to tune and see how much RWHP I have. Real concerned about my stock block
should have gone dart... I expect to make 450 to 500rwhp.
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