What boost were they running?i dont think the block-head will hold up. i do know in the 855 bc2 475hp twin turbo engines. they ran great for about 150,000-200,000 miles then they were junk. the top of the block busted where the head bolts screw into bad . also heads cracked from valve seats to the injector holes real bad.i sold all my twin setups and went with the big hi-altitude 3801919 blowers and still killed em.