In conversing with some Cummins rep's several years back, they said the exact thing. Every pound of boost produces about 10 HP. So when I first installed a gauge on my 91 1/2, I installed a boost gauge, and sure enough, I had a max of 16 PSI. The engine was rated at 160 HP. My 94 has some upgrades, and I have had it on a dyno that said I was producing about 300 HP... ... . yep, the boost gauge reads 30 PSI max. So I thnk this is a pretty good rule of thumb. BTW, I do have the stock turbo.
Wayne
amsoilman