i would try to keep it under 25psi for sure (the cummins specified max boost for automotive b5.9s!) just to make sure that you dont end up lifting the head and popping a gasket before everything gets a good chance to heat cycle and seat itself.

 

ok guys i took it for about a 100 mile round trip of freeway and hiway driving. i pushed her fater and harder ever time i went threw the gears keeping it below 20psi just for safety even know the head is o-rings with head studs. i ran it at 75 at 2100RPm for a constant 25-30minuts and she ran beutifly

 

did u post any pics of the finished mill ?

 

thers a thread on here that has all my progress shots